Rambda

Rambda is smaller and faster alternative to the popular functional programming library Ramda. - Documentation

Example use

import { compose, map, filter } from 'rambda'

const result = compose(
  map(x => x * 2),
  filter(x => x > 2)
)([1, 2, 3, 4])
// => [6, 8]

You can test this example in Rambda's REPL

Differences between Rambda and Ramda
API
Changelog

Rambda's advantages

TypeScript included

TypeScript definitions are included in the library, in comparison to Ramda, where you need to additionally install @types/ramda.

Still, you need to be aware that functional programming features in TypeScript are in development, which means that using R.compose/R.pipe can be problematic.

Important - Rambda version 7.1.0(or higher) requires TypeScript version 4.3.3(or higher).

Understandable source code due to little usage of internals

Ramda uses a lot of internals, which hides a lot of logic. Reading the full source code of a method can be challenging.

Better VSCode experience

If the project is written in Javascript, then go to source definition action will lead you to actual implementation of the method.

Immutable TS definitions

You can use immutable version of Rambda definitions, which is linted with ESLint functional/prefer-readonly-type plugin.

import {add} from 'rambda/immutable'

Deno support

Latest version of Ramba available for Deno users is 3 years old. This is not the case with Rambda as most of recent releases are available for Deno users.

Also, Rambda provides you with included TS definitions:

// Deno extension(https://marketplace.visualstudio.com/items?itemName=denoland.vscode-deno)
// is installed and initialized
import * as R from "https://deno.land/x/rambda/mod.ts";
import * as Ramda from "https://deno.land/x/ramda/mod.ts";

R.add(1)('foo') // => will trigger warning in VSCode as it should
Ramda.add(1)('foo') // => will not trigger warning in VSCode

Dot notation for `R.path`, `R.paths`, `R.assocPath` and `R.lensPath`

Standard usage of R.path is R.path(['a', 'b'], {a: {b: 1} }).

In Rambda you have the choice to use dot notation(which is arguably more readable):

R.path('a.b', {a: {b: 1} })

Comma notation for `R.pick` and `R.omit`

Similar to dot notation, but the separator is comma(,) instead of dot(.).

R.pick('a,b', {a: 1 , b: 2, c: 3} })
// No space allowed between properties

Speed

Rambda is generally more performant than Ramda as the benchmarks can prove that.

Support

One of the main issues with Ramda is the slow process of releasing new versions. This is not the case with Rambda as releases are made on regular basis.

Missing Ramda methods

construct - Using classes is not very functional programming oriented.
constructN - same as above
into - no support for transducer as it is overly complex to implement, understand and read.
invert - overly complicated and limited use case
invertObj
invoker
keysIn - we shouldn't encourage extending object with .prototype
lift
liftN
mapAccum - Ramda example doesn't looks convincing
mapAccumRight
memoizeWith - hard to imagine its usage in context of R.pipe/R.compose
mergeDeepWith - limited use case
mergeDeepWithKey
mergeWithKey
nAry - hard to argument about and hard to create meaningful TypeScript definitions
nthArg - limited use case
o - enough TypeScript issues with R.pipe/R.compose to add more composition methods
otherwise - naming is confusing
pair - left-pad types of debacles happens partially because of such methods that should not be hidden, bur rather part of your code base even if they need to exist.
partialRight - I dislike R.partial, so I don't want to add more methods that are based on it
pipeWith
project - naming is confusing, but also limited use case
promap
reduceRight - I find right/left methods confusing so I added them only where it makes sense.
reduceWhile - functions with 4 inputs - I think that even 3 is too much
reduced
remove - nice name but it is too generic. Also, Rambdax has such method and there it works very differently
scan - hard to explain
sequence
splitWhenever
symmetricDifferenceWith
andThen
toPairsIn
transduce - currently is out of focus
traverse - same as above
unary
uncurryN
unfold - similar to R.scan and I find that it doesn't help with readability
unionWith - why it has its usage, I want to limit number of methods that accept more than 2 arguments
until
useWith - hard to explain
valuesIn
xprod - limited use case
thunkify
__ - placeholder method allows user to further customize the method call. While, it seems useful initially, the price is too high in terms of complexity for TypeScript definitions. If it is not easy exressable in TypeScript, it is not worth it as Rambda is a TypeScript first library.

The following methods are not going to be added(reason for exclusion is provided as a comment):

Install

yarn add rambda
For UMD usage either use ./dist/rambda.umd.js or the following CDN link:

https://unpkg.com/rambda@CURRENT_VERSION/dist/rambda.umd.js

with deno

import {add} from "https://deno.land/x/rambda/mod.ts";

Differences between Rambda and Ramda

Rambda's type detects async functions and unresolved Promises. The returned values are 'Async' and 'Promise'.
Rambda's type handles NaN input, in which case it returns NaN.
Rambda's forEach can iterate over objects not only arrays.
Rambda's map, filter, partition when they iterate over objects, they pass property and input object as predicate's argument.
Rambda's filter returns empty array with bad input(null or undefined), while Ramda throws.
Ramda's clamp work with strings, while Rambda's method work only with numbers.
Ramda's indexOf/lastIndexOf work with strings and lists, while Rambda's method work only with lists as iterable input.
Error handling, when wrong inputs are provided, may not be the same. This difference will be better documented once all brute force tests are completed.
TypeScript definitions between rambda and @types/ramda may vary.

If you need more Ramda methods in Rambda, you may either submit a PR or check the extended version of Rambda - Rambdax. In case of the former, you may want to consult with Rambda contribution guidelines.

Benchmarks

There are methods which are benchmarked only with Ramda and Rambda(i.e. no Lodash).

Note that some of these methods, are called with and without curring. This is done in order to give more detailed performance feedback.

The benchmarks results are produced from latest versions of Rambda, Lodash(4.17.21) and Ramda(0.30.1).

method	Rambda	Ramda	Lodash
add	Fastest	21.52% slower	82.15% slower
adjust	8.48% slower	Fastest
all	Fastest	7.18% slower
allPass	Fastest	88.25% slower
allPass	Fastest	98.56% slower
and	Fastest	89.09% slower
any	Fastest	92.87% slower	45.82% slower
anyPass	Fastest	98.25% slower
append	Fastest	2.07% slower
applySpec	Fastest	80.43% slower
assoc	72.32% slower	60.08% slower	Fastest
clone	Fastest	91.86% slower	86.48% slower
compose	6.07% slower	16.89% slower	Fastest
converge	78.63% slower	Fastest
curry	Fastest	28.86% slower
curryN	Fastest	41.05% slower
defaultTo	Fastest	48.91% slower
drop	Fastest	82.35% slower
dropLast	Fastest	86.74% slower
equals	58.37% slower	96.73% slower	Fastest
filter	6.7% slower	72.03% slower	Fastest
find	Fastest	85.14% slower	42.65% slower
findIndex	Fastest	86.48% slower	72.27% slower
flatten	Fastest	85.68% slower	3.57% slower
ifElse	Fastest	58.56% slower
includes	Fastest	81.64% slower
indexOf	Fastest	80.17% slower
indexOf	Fastest	82.2% slower
init	Fastest	92.24% slower	13.3% slower
is	Fastest	57.69% slower
isEmpty	Fastest	97.14% slower	54.99% slower
last	Fastest	93.43% slower	5.28% slower
lastIndexOf	Fastest	85.19% slower
map	Fastest	86.6% slower	11.73% slower
match	Fastest	44.83% slower
merge	Fastest	12.21% slower	55.76% slower
none	Fastest	96.48% slower
objOf	Fastest	38.05% slower
omit	Fastest	69.95% slower	97.34% slower
over	Fastest	56.23% slower
path	37.81% slower	77.81% slower	Fastest
pick	Fastest	19.07% slower	80.2% slower
pipe	Fastest	0.11% slower
prop	Fastest	87.95% slower
propEq	Fastest	91.92% slower
range	Fastest	61.8% slower	57.44% slower
reduce	60.48% slower	77.1% slower	Fastest
repeat	48.57% slower	68.98% slower	Fastest
replace	33.45% slower	33.99% slower	Fastest
set	Fastest	50.35% slower
sort	Fastest	40.23% slower
sortBy	Fastest	25.29% slower	56.88% slower
split	Fastest	55.37% slower	17.64% slower
splitEvery	Fastest	71.98% slower
take	Fastest	91.96% slower	4.72% slower
takeLast	Fastest	93.39% slower	19.22% slower
test	Fastest	82.34% slower
type	Fastest	48.6% slower
uniq	Fastest	84.9% slower
uniqBy	51.93% slower	Fastest
uniqWith	8.29% slower	Fastest
uniqWith	14.23% slower	Fastest
update	Fastest	52.35% slower
view	Fastest	76.15% slower

Used by

API

add

It adds a and b.

Try this R.add example in Rambda REPL

addIndex

Try this R.addIndex example in Rambda REPL

addIndexRight

Same as R.addIndex, but it will passed indexes are decreasing, instead of increasing.

adjust


adjust<T>(index: number, replaceFn: (x: T) => T, list: T[]): T[]

It replaces index in array list with the result of replaceFn(list[i]).

Try this R.adjust example in Rambda REPL

adjust<T>(index: number, replaceFn: (x: T) => T, list: T[]): T[];
adjust<T>(index: number, replaceFn: (x: T) => T): (list: T[]) => T[];

import { cloneList } from './_internals/cloneList.js'
import { curry } from './curry.js'

function adjustFn(
  index, replaceFn, list
){
  const actualIndex = index < 0 ? list.length + index : index
  if (index >= list.length || actualIndex < 0) return list

  const clone = cloneList(list)
  clone[ actualIndex ] = replaceFn(clone[ actualIndex ])

  return clone
}

export const adjust = curry(adjustFn)

import { add } from './add.js'
import { adjust } from './adjust.js'
import { pipe } from './pipe.js'

const list = [ 0, 1, 2 ]
const expected = [ 0, 11, 2 ]

test('happy', () => {})

test('happy', () => {
  expect(adjust(
    1, add(10), list
  )).toEqual(expected)
})

test('with curring type 1 1 1', () => {
  expect(adjust(1)(add(10))(list)).toEqual(expected)
})

test('with curring type 1 2', () => {
  expect(adjust(1)(add(10), list)).toEqual(expected)
})

test('with curring type 2 1', () => {
  expect(adjust(1, add(10))(list)).toEqual(expected)
})

test('with negative index', () => {
  expect(adjust(
    -2, add(10), list
  )).toEqual(expected)
})

test('when index is out of bounds', () => {
  const list = [ 0, 1, 2, 3 ]
  expect(adjust(
    4, add(1), list
  )).toEqual(list)
  expect(adjust(
    -5, add(1), list
  )).toEqual(list)
})

all


all<T>(predicate: (x: T) => boolean, list: T[]): boolean

It returns true, if all members of array list returns true, when applied as argument to predicate function.

Try this R.all example in Rambda REPL

all<T>(predicate: (x: T) => boolean, list: T[]): boolean;
all<T>(predicate: (x: T) => boolean): (list: T[]) => boolean;

export function all(predicate, list){
  if (arguments.length === 1) return _list => all(predicate, _list)

  for (let i = 0; i < list.length; i++){
    if (!predicate(list[ i ])) return false
  }

  return true
}

import { all } from './all.js'

const list = [ 0, 1, 2, 3, 4 ]

test('when true', () => {
  const fn = x => x > -1

  expect(all(fn)(list)).toBeTrue()
})

test('when false', () => {
  const fn = x => x > 2

  expect(all(fn, list)).toBeFalse()
})

import {all} from 'rambda'

describe('all', () => {
  it('happy', () => {
    const result = all(
      x => {
        x // $ExpectType number
        return x > 0
      },
      [1, 2, 3]
    )
    result // $ExpectType boolean
  })
  it('curried needs a type', () => {
    const result = all<number>(x => {
      x // $ExpectType number
      return x > 0
    })([1, 2, 3])
    result // $ExpectType boolean
  })
})

allPass


allPass<T>(predicates: ((x: T) => boolean)[]): (input: T) => boolean

It returns true, if all functions of predicates return true, when input is their argument.

Try this R.allPass example in Rambda REPL

allPass<T>(predicates: ((x: T) => boolean)[]): (input: T) => boolean;
allPass<T>(predicates: ((...inputs: T[]) => boolean)[]): (...inputs: T[]) => boolean;

export function allPass(predicates){
  return (...input) => {
    let counter = 0
    while (counter < predicates.length){
      if (!predicates[ counter ](...input)){
        return false
      }
      counter++
    }

    return true
  }
}

import { allPass } from './allPass.js'

test('happy', () => {
  const rules = [ x => typeof x === 'number', x => x > 10, x => x * 7 < 100 ]

  expect(allPass(rules)(11)).toBeTrue()

  expect(allPass(rules)(undefined)).toBeFalse()
})

test('when returns true', () => {
  const conditionArr = [ val => val.a === 1, val => val.b === 2 ]

  expect(allPass(conditionArr)({
    a : 1,
    b : 2,
  })).toBeTrue()
})

test('when returns false', () => {
  const conditionArr = [ val => val.a === 1, val => val.b === 3 ]

  expect(allPass(conditionArr)({
    a : 1,
    b : 2,
  })).toBeFalse()
})

test('works with multiple inputs', () => {
  const fn = function (
    w, x, y, z
  ){
    return w + x === y + z
  }
  expect(allPass([ fn ])(
    3, 3, 3, 3
  )).toBeTrue()
})

import {allPass, filter} from 'rambda'

describe('allPass', () => {
  it('happy', () => {
    const x = allPass<number>([
      y => {
        y // $ExpectType number
        return typeof y === 'number'
      },
      y => {
        return y > 0
      },
    ])(11)

    x // $ExpectType boolean
  })
  it('issue #642', () => {
    const isGreater = (num: number) => num > 5
    const pred = allPass([isGreater])
    const xs = [0, 1, 2, 3]

    const filtered1 = filter(pred)(xs)
    filtered1 // $ExpectType number[]
    const filtered2 = xs.filter(pred)
    filtered2 // $ExpectType number[]
  })
  it('issue #604', () => {
    const plusEq = function(w: number, x: number, y: number, z: number) {
      return w + x === y + z
    }
    const result = allPass([plusEq])(3, 3, 3, 3)

    result // $ExpectType boolean
  })
})

always

It returns function that always returns x.

Try this R.always example in Rambda REPL

and

Logical AND

Try this R.and example in Rambda REPL

any


any<T>(predicate: (x: T) => boolean, list: T[]): boolean

It returns true, if at least one member of list returns true, when passed to a predicate function.

Try this R.any example in Rambda REPL

any<T>(predicate: (x: T) => boolean, list: T[]): boolean;
any<T>(predicate: (x: T) => boolean): (list: T[]) => boolean;

export function any(predicate, list){
  if (arguments.length === 1) return _list => any(predicate, _list)

  let counter = 0
  while (counter < list.length){
    if (predicate(list[ counter ], counter)){
      return true
    }
    counter++
  }

  return false
}

import { any } from './any.js'

const list = [ 1, 2, 3 ]

test('happy', () => {
  expect(any(x => x < 0, list)).toBeFalse()
})

test('with curry', () => {
  expect(any(x => x > 2)(list)).toBeTrue()
})

import {any} from 'rambda'

describe('R.any', () => {
  it('happy', () => {
    const result = any(
      x => {
        x // $ExpectType number
        return x > 2
      },
      [1, 2, 3]
    )
    result // $ExpectType boolean
  })

  it('when curried needs a type', () => {
    const result = any<number>(x => {
      x // $ExpectType number
      return x > 2
    })([1, 2, 3])
    result // $ExpectType boolean
  })
})

anyPass


anyPass<T>(predicates: ((x: T) => boolean)[]): (input: T) => boolean

It accepts list of predicates and returns a function. This function with its input will return true, if any of predicates returns true for this input.

Try this R.anyPass example in Rambda REPL

anyPass<T>(predicates: ((x: T) => boolean)[]): (input: T) => boolean;
anyPass<T>(predicates: ((...inputs: T[]) => boolean)[]): (...inputs: T[]) => boolean;

export function anyPass(predicates){
  return (...input) => {
    let counter = 0
    while (counter < predicates.length){
      if (predicates[ counter ](...input)){
        return true
      }
      counter++
    }

    return false
  }
}

import { anyPass } from './anyPass.js'

test('happy', () => {
  const rules = [ x => typeof x === 'string', x => x > 10 ]
  const predicate = anyPass(rules)
  expect(predicate('foo')).toBeTrue()
  expect(predicate(6)).toBeFalse()
})

test('happy', () => {
  const rules = [ x => typeof x === 'string', x => x > 10 ]

  expect(anyPass(rules)(11)).toBeTrue()
  expect(anyPass(rules)(undefined)).toBeFalse()
})

const obj = {
  a : 1,
  b : 2,
}

test('when returns true', () => {
  const conditionArr = [ val => val.a === 1, val => val.a === 2 ]

  expect(anyPass(conditionArr)(obj)).toBeTrue()
})

test('when returns false + curry', () => {
  const conditionArr = [ val => val.a === 2, val => val.b === 3 ]

  expect(anyPass(conditionArr)(obj)).toBeFalse()
})

test('with empty predicates list', () => {
  expect(anyPass([])(3)).toBeFalse()
})

test('works with multiple inputs', () => {
  const fn = function (
    w, x, y, z
  ){
    console.log(
      w, x, y, z
    )

    return w + x === y + z
  }
  expect(anyPass([ fn ])(
    3, 3, 3, 3
  )).toBeTrue()
})

import {anyPass, filter} from 'rambda'

describe('anyPass', () => {
  it('happy', () => {
    const x = anyPass<number>([
      y => {
        y // $ExpectType number
        return typeof y === 'number'
      },
      y => {
        return y > 0
      },
    ])(11)

    x // $ExpectType boolean
  })
  it('issue #604', () => {
    const plusEq = function(w: number, x: number, y: number, z: number) {
      return w + x === y + z
    }
    const result = anyPass([plusEq])(3, 3, 3, 3)

    result // $ExpectType boolean
  })
  it('issue #642', () => {
    const isGreater = (num: number) => num > 5
    const pred = anyPass([isGreater])
    const xs = [0, 1, 2, 3]

    const filtered1 = filter(pred)(xs)
    filtered1 // $ExpectType number[]
    const filtered2 = xs.filter(pred)
    filtered2 // $ExpectType number[]
  })
  it('functions as a type guard', () => {
    const isString = (x: unknown): x is string => typeof x === 'string'
    const isNumber = (x: unknown): x is number => typeof x === 'number'
    const isBoolean = (x: unknown): x is boolean => typeof x === 'boolean'

    const isStringNumberOrBoolean = anyPass([isString, isNumber, isBoolean])

    isStringNumberOrBoolean // $ExpectType (input: unknown) => boolean

    const aValue: unknown = 1

    if (isStringNumberOrBoolean(aValue)) {
      aValue // $ExpectType unknown
    }
  })
})

ap


ap<T, U>(fns: Array<(a: T) => U>[], vs: T[]): U[]

It takes a list of functions and a list of values. Then it returns a list of values obtained by applying each function to each value.

Try this R.ap example in Rambda REPL

ap<T, U>(fns: Array<(a: T) => U>[], vs: T[]): U[];
ap<T, U>(fns: Array<(a: T) => U>): (vs: T[]) => U[];
ap<R, A, B>(fn: (r: R, a: A) => B, fn1: (r: R) => A): (r: R) => B;

export function ap(functions, input){
  if (arguments.length === 1){
    return _inputs => ap(functions, _inputs)
  }

  return functions.reduce((acc, fn) => [ ...acc, ...input.map(fn) ], [])
}

import { ap } from './ap.js'

function mult2(x){
  return x * 2
}
function plus3(x){
  return x + 3
}

test('happy', () => {
  expect(ap([ mult2, plus3 ], [ 1, 2, 3 ])).toEqual([ 2, 4, 6, 4, 5, 6 ])
})

aperture


aperture<N extends number, T>(n: N, list: T[]): Array<Tuple<T, N>> | []

It returns a new list, composed of consecutive n-tuples from a list.

Try this R.aperture example in Rambda REPL

aperture<N extends number, T>(n: N, list: T[]): Array<Tuple<T, N>> | [];
aperture<N extends number>(n: N): <T>(list: T[]) => Array<Tuple<T, N>> | [];

export function aperture(step, list){
  if (arguments.length === 1){
    return _list => aperture(step, _list)
  }
  if (step > list.length) return []
  let idx = 0
  const limit = list.length - (step - 1)
  const acc = new Array(limit)
  while (idx < limit){
    acc[ idx ] = list.slice(idx, idx + step)
    idx += 1
  }

  return acc
}

import { aperture } from './aperture.js'

const list = [ 1, 2, 3, 4, 5, 6, 7 ]

test('happy', () => {
  expect(aperture(1, list)).toEqual([ [ 1 ], [ 2 ], [ 3 ], [ 4 ], [ 5 ], [ 6 ], [ 7 ] ])
  expect(aperture(2, list)).toEqual([
    [ 1, 2 ],
    [ 2, 3 ],
    [ 3, 4 ],
    [ 4, 5 ],
    [ 5, 6 ],
    [ 6, 7 ],
  ])
  expect(aperture(3, list)).toEqual([
    [ 1, 2, 3 ],
    [ 2, 3, 4 ],
    [ 3, 4, 5 ],
    [ 4, 5, 6 ],
    [ 5, 6, 7 ],
  ])
  expect(aperture(8, list)).toEqual([])
})

append


append<T>(xToAppend: T, iterable: T[]): T[]

It adds element x at the end of iterable.

Try this R.append example in Rambda REPL

append<T>(xToAppend: T, iterable: T[]): T[];
append<T, U>(xToAppend: T, iterable: IsFirstSubtypeOfSecond<T, U>[]) : U[];
append<T>(xToAppend: T): <U>(iterable: IsFirstSubtypeOfSecond<T, U>[]) => U[];
append<T>(xToAppend: T): (iterable: T[]) => T[];

import { cloneList } from './_internals/cloneList.js'

export function append(x, input){
  if (arguments.length === 1) return _input => append(x, _input)

  if (typeof input === 'string') return input.split('').concat(x)

  const clone = cloneList(input)
  clone.push(x)

  return clone
}

import { append } from './append.js'

test('happy', () => {
  expect(append('tests', [ 'write', 'more' ])).toEqual([
    'write',
    'more',
    'tests',
  ])
})

test('append to empty array', () => {
  expect(append('tests')([])).toEqual([ 'tests' ])
})

test('with strings', () => {
  expect(append('o', 'fo')).toEqual([ 'f', 'o', 'o' ])
})

import {append, prepend} from 'rambda'

const listOfNumbers = [1, 2, 3]
const listOfNumbersAndStrings = [1, 'b', 3]

describe('R.append/R.prepend', () => {
  describe("with the same primitive type as the array's elements", () => {
    it('uncurried', () => {
      // @ts-expect-error
      append('d', listOfNumbers)
      // @ts-expect-error
      prepend('d', listOfNumbers)
      append(4, listOfNumbers) // $ExpectType number[]
      prepend(4, listOfNumbers) // $ExpectType number[]
    })

    it('curried', () => {
      // @ts-expect-error
      append('d')(listOfNumbers)
      append(4)(listOfNumbers) // $ExpectType number[]
      prepend(4)(listOfNumbers) // $ExpectType number[]
    })
  })

  describe("with a subtype of the array's elements", () => {
    it('uncurried', () => {
      // @ts-expect-error
      append(true, listOfNumbersAndStrings)
      append(4, listOfNumbersAndStrings) // $ExpectType (string | number)[]
      prepend(4, listOfNumbersAndStrings) // $ExpectType (string | number)[]
    })

    it('curried', () => {
      // @ts-expect-error
      append(true)(listOfNumbersAndStrings)
      append(4)(listOfNumbersAndStrings) // $ExpectType (string | number)[]
      prepend(4)(listOfNumbersAndStrings) // $ExpectType (string | number)[]
    })
  })

  describe("expanding the type of the array's elements", () => {
    it('uncurried', () => {
      // @ts-expect-error
      append('d', listOfNumbers)
      append<string | number>('d', listOfNumbers) // $ExpectType (string | number)[]
      prepend<string | number>('d', listOfNumbers) // $ExpectType (string | number)[]
    })

    it('curried', () => {
      // @ts-expect-error
      append('d')(listOfNumbers)
      const appendD = append('d')
      appendD<string | number>(listOfNumbers) // $ExpectType (string | number)[]
      const prependD = prepend('d')
      prependD<string | number>(listOfNumbers) // $ExpectType (string | number)[]
    })
  })
})

apply


apply<T = any>(fn: (...args: any[]) => T, args: any[]): T

It applies function fn to the list of arguments.

This is useful for creating a fixed-arity function from a variadic function. fn should be a bound function if context is significant.

Try this R.apply example in Rambda REPL

apply<T = any>(fn: (...args: any[]) => T, args: any[]): T;
apply<T = any>(fn: (...args: any[]) => T): (args: any[]) => T;

export function apply(fn, args){
  if (arguments.length === 1){
    return _args => apply(fn, _args)
  }

  return fn.apply(this, args)
}

import { apply } from './apply.js'
import { bind } from './bind.js'
import { identity } from './identity.js'

test('happy', () => {
  expect(apply(identity, [ 1, 2, 3 ])).toBe(1)
})

test('applies function to argument list', () => {
  expect(apply(Math.max, [ 1, 2, 3, -99, 42, 6, 7 ])).toBe(42)
})

test('provides no way to specify context', () => {
  const obj = {
    method (){
      return this === obj
    },
  }
  expect(apply(obj.method, [])).toBeFalse()
  expect(apply(bind(obj.method, obj), [])).toBeTrue()
})

import {apply, identity} from 'rambda'

describe('R.apply', () => {
  it('happy', () => {
    const result = apply<number>(identity, [1, 2, 3])

    result // $ExpectType number
  })
  it('curried', () => {
    const fn = apply<number>(identity)
    const result = fn([1, 2, 3])

    result // $ExpectType number
  })
})

applySpec


applySpec<Spec extends Record<string, AnyFunction>>(
  spec: Spec
): (
  ...args: Parameters<ValueOfRecord<Spec>>
) => { [Key in keyof Spec]: ReturnType<Spec[Key]> }

Try this R.applySpec example in Rambda REPL

applySpec<Spec extends Record<string, AnyFunction>>(
  spec: Spec
): (
  ...args: Parameters<ValueOfRecord<Spec>>
) => { [Key in keyof Spec]: ReturnType<Spec[Key]> };
applySpec<T>(spec: any): (...args: unknown[]) => T;

import { isArray } from './_internals/isArray.js'

// recursively traverse the given spec object to find the highest arity function
export function __findHighestArity(spec, max = 0){
  for (const key in spec){
    if (spec.hasOwnProperty(key) === false || key === 'constructor') continue

    if (typeof spec[ key ] === 'object'){
      max = Math.max(max, __findHighestArity(spec[ key ]))
    }

    if (typeof spec[ key ] === 'function'){
      max = Math.max(max, spec[ key ].length)
    }
  }

  return max
}

function __filterUndefined(){
  const defined = []
  let i = 0
  const l = arguments.length
  while (i < l){
    if (typeof arguments[ i ] === 'undefined') break
    defined[ i ] = arguments[ i ]
    i++
  }

  return defined
}

function __applySpecWithArity(
  spec, arity, cache
){
  const remaining = arity - cache.length

  if (remaining === 1)
    return x =>
      __applySpecWithArity(
        spec, arity, __filterUndefined(...cache, x)
      )
  if (remaining === 2)
    return (x, y) =>
      __applySpecWithArity(
        spec, arity, __filterUndefined(
          ...cache, x, y
        )
      )
  if (remaining === 3)
    return (
      x, y, z
    ) =>
      __applySpecWithArity(
        spec, arity, __filterUndefined(
          ...cache, x, y, z
        )
      )
  if (remaining === 4)
    return (
      x, y, z, a
    ) =>
      __applySpecWithArity(
        spec,
        arity,
        __filterUndefined(
          ...cache, x, y, z, a
        )
      )
  if (remaining > 4)
    return (...args) =>
      __applySpecWithArity(
        spec, arity, __filterUndefined(...cache, ...args)
      )

  // handle spec as Array
  if (isArray(spec)){
    const ret = []
    let i = 0
    const l = spec.length
    for (; i < l; i++){
      // handle recursive spec inside array
      if (typeof spec[ i ] === 'object' || isArray(spec[ i ])){
        ret[ i ] = __applySpecWithArity(
          spec[ i ], arity, cache
        )
      }
      // apply spec to the key
      if (typeof spec[ i ] === 'function'){
        ret[ i ] = spec[ i ](...cache)
      }
    }

    return ret
  }

  // handle spec as Object
  const ret = {}
  // apply callbacks to each property in the spec object
  for (const key in spec){
    if (spec.hasOwnProperty(key) === false || key === 'constructor') continue

    // apply the spec recursively
    if (typeof spec[ key ] === 'object'){
      ret[ key ] = __applySpecWithArity(
        spec[ key ], arity, cache
      )
      continue
    }

    // apply spec to the key
    if (typeof spec[ key ] === 'function'){
      ret[ key ] = spec[ key ](...cache)
    }
  }

  return ret
}

export function applySpec(spec, ...args){
  // get the highest arity spec function, cache the result and pass to __applySpecWithArity
  const arity = __findHighestArity(spec)

  if (arity === 0){
    return () => ({})
  }
  const toReturn = __applySpecWithArity(
    spec, arity, args
  )

  return toReturn
}

import { applySpec as applySpecRamda, nAry } from 'ramda'

import {
  add,
  always,
  compose,
  dec,
  inc,
  map,
  path,
  prop,
  T,
} from '../rambda.js'
import { applySpec } from './applySpec.js'

test('different than Ramda when bad spec', () => {
  const result = applySpec({ sum : { a : 1 } })(1, 2)
  const ramdaResult = applySpecRamda({ sum : { a : 1 } })(1, 2)
  expect(result).toEqual({})
  expect(ramdaResult).toEqual({ sum : { a : {} } })
})

test('works with empty spec', () => {
  expect(applySpec({})()).toEqual({})
  expect(applySpec([])(1, 2)).toEqual({})
  expect(applySpec(null)(1, 2)).toEqual({})
})

test('works with unary functions', () => {
  const result = applySpec({
    v : inc,
    u : dec,
  })(1)
  const expected = {
    v : 2,
    u : 0,
  }
  expect(result).toEqual(expected)
})

test('works with binary functions', () => {
  const result = applySpec({ sum : add })(1, 2)
  expect(result).toEqual({ sum : 3 })
})

test('works with nested specs', () => {
  const result = applySpec({
    unnested : always(0),
    nested   : { sum : add },
  })(1, 2)
  const expected = {
    unnested : 0,
    nested   : { sum : 3 },
  }
  expect(result).toEqual(expected)
})

test('works with arrays of nested specs', () => {
  const result = applySpec({
    unnested : always(0),
    nested   : [ { sum : add } ],
  })(1, 2)

  expect(result).toEqual({
    unnested : 0,
    nested   : [ { sum : 3 } ],
  })
})

test('works with arrays of spec objects', () => {
  const result = applySpec([ { sum : add } ])(1, 2)

  expect(result).toEqual([ { sum : 3 } ])
})

test('works with arrays of functions', () => {
  const result = applySpec([ map(prop('a')), map(prop('b')) ])([
    {
      a : 'a1',
      b : 'b1',
    },
    {
      a : 'a2',
      b : 'b2',
    },
  ])
  const expected = [
    [ 'a1', 'a2' ],
    [ 'b1', 'b2' ],
  ]
  expect(result).toEqual(expected)
})

test('works with a spec defining a map key', () => {
  expect(applySpec({ map : prop('a') })({ a : 1 })).toEqual({ map : 1 })
})

test('cannot retains the highest arity', () => {
  const f = applySpec({
    f1 : nAry(2, T),
    f2 : nAry(5, T),
  })
  const fRamda = applySpecRamda({
    f1 : nAry(2, T),
    f2 : nAry(5, T),
  })
  expect(f).toHaveLength(0)
  expect(fRamda).toHaveLength(5)
})

test('returns a curried function', () => {
  expect(applySpec({ sum : add })(1)(2)).toEqual({ sum : 3 })
})

// Additional tests
// ============================================
test('arity', () => {
  const spec = {
    one   : x1 => x1,
    two   : (x1, x2) => x1 + x2,
    three : (
      x1, x2, x3
    ) => x1 + x2 + x3,
  }
  expect(applySpec(
    spec, 1, 2, 3
  )).toEqual({
    one   : 1,
    two   : 3,
    three : 6,
  })
})

test('arity over 5 arguments', () => {
  const spec = {
    one   : x1 => x1,
    two   : (x1, x2) => x1 + x2,
    three : (
      x1, x2, x3
    ) => x1 + x2 + x3,
    four : (
      x1, x2, x3, x4
    ) => x1 + x2 + x3 + x4,
    five : (
      x1, x2, x3, x4, x5
    ) => x1 + x2 + x3 + x4 + x5,
  }
  expect(applySpec(
    spec, 1, 2, 3, 4, 5
  )).toEqual({
    one   : 1,
    two   : 3,
    three : 6,
    four  : 10,
    five  : 15,
  })
})

test('curried', () => {
  const spec = {
    one   : x1 => x1,
    two   : (x1, x2) => x1 + x2,
    three : (
      x1, x2, x3
    ) => x1 + x2 + x3,
  }
  expect(applySpec(spec)(1)(2)(3)).toEqual({
    one   : 1,
    two   : 3,
    three : 6,
  })
})

test('curried over 5 arguments', () => {
  const spec = {
    one   : x1 => x1,
    two   : (x1, x2) => x1 + x2,
    three : (
      x1, x2, x3
    ) => x1 + x2 + x3,
    four : (
      x1, x2, x3, x4
    ) => x1 + x2 + x3 + x4,
    five : (
      x1, x2, x3, x4, x5
    ) => x1 + x2 + x3 + x4 + x5,
  }
  expect(applySpec(spec)(1)(2)(3)(4)(5)).toEqual({
    one   : 1,
    two   : 3,
    three : 6,
    four  : 10,
    five  : 15,
  })
})

test('undefined property', () => {
  const spec = { prop : path([ 'property', 'doesnt', 'exist' ]) }
  expect(applySpec(spec, {})).toEqual({ prop : undefined })
})

test('restructure json object', () => {
  const spec = {
    id          : path('user.id'),
    name        : path('user.firstname'),
    profile     : path('user.profile'),
    doesntExist : path('user.profile.doesntExist'),
    info        : { views : compose(inc, prop('views')) },
    type        : always('playa'),
  }

  const data = {
    user : {
      id        : 1337,
      firstname : 'john',
      lastname  : 'shaft',
      profile   : 'shaft69',
    },
    views : 42,
  }

  expect(applySpec(spec, data)).toEqual({
    id          : 1337,
    name        : 'john',
    profile     : 'shaft69',
    doesntExist : undefined,
    info        : { views : 43 },
    type        : 'playa',
  })
})

import {multiply, applySpec, inc, dec, add} from 'rambda'

describe('applySpec', () => {
  it('ramda 1', () => {
    const result = applySpec({
      v: inc,
      u: dec,
    })(1)
    result // $ExpectType { v: number; u: number; }
  })
  it('ramda 1', () => {
    interface Output {
      sum: number,
      multiplied: number,
    }
    const result = applySpec<Output>({
      sum: add,
      multiplied: multiply,
    })(1, 2)

    result // $ExpectType Output
  })
})

applyTo

Try this R.applyTo example in Rambda REPL

ascend

Try this R.ascend example in Rambda REPL

assoc

It makes a shallow clone of obj with setting or overriding the property prop with newValue.

Try this R.assoc example in Rambda REPL

assocPath


assocPath<Output>(path: Path, newValue: any, obj: object): Output

It makes a shallow clone of obj with setting or overriding with newValue the property found with path.

Try this R.assocPath example in Rambda REPL

assocPath<Output>(path: Path, newValue: any, obj: object): Output;
assocPath<Output>(path: Path, newValue: any): (obj: object) => Output;
assocPath<Output>(path: Path): (newValue: any) => (obj: object) => Output;

import { cloneList } from './_internals/cloneList.js'
import { createPath } from './_internals/createPath.js'
import { isArray } from './_internals/isArray.js'
import { isIndexInteger } from './_internals/isInteger.js'
import { assocFn } from './assoc.js'
import { curry } from './curry.js'

export function assocPathFn(
  path, newValue, input
){
  const pathArrValue = createPath(path)
  if (pathArrValue.length === 0) return newValue

  const index = pathArrValue[ 0 ]
  if (pathArrValue.length > 1){
    const condition =
      typeof input !== 'object' ||
      input === null ||
      !input.hasOwnProperty(index)

    const nextInput = condition ?
      isIndexInteger(pathArrValue[ 1 ]) ?
        [] :
        {} :
      input[ index ]

    newValue = assocPathFn(
      Array.prototype.slice.call(pathArrValue, 1),
      newValue,
      nextInput
    )
  }

  if (isIndexInteger(index) && isArray(input)){
    const arr = cloneList(input)
    arr[ index ] = newValue

    return arr
  }

  return assocFn(
    index, newValue, input
  )
}

export const assocPath = curry(assocPathFn)

import { assocPathFn } from './assocPath.js'

test.only('happy', () => {
  const path = 'a.c.1'
  const input = {
    a : {
      b : 1,
      c : [ 1, 2 ],
    },
  }
  assocPathFn(
    path, 3, input
  )
  expect(input).toEqual({
    a : {
      b : 1,
      c : [ 1, 2 ],
    },
  })
})

test('string can be used as path input', () => {
  const testObj = {
    a : [ { b : 1 }, { b : 2 } ],
    d : 3,
  }
  const result1 = assocPathFn(
    [ 'a', 0, 'b' ], 10, testObj
  )
  const result2 = assocPathFn(
    'a.0.b', 10, testObj
  )

  const expected = {
    a : [ { b : 10 }, { b : 2 } ],
    d : 3,
  }
  expect(result1).toEqual(expected)
  expect(result2).toEqual(expected)
})

test('difference with ramda - doesn\'t overwrite primitive values with keys in the path', () => {
  const obj = { a : 'str' }
  const result = assocPath(
    [ 'a', 'b' ], 42, obj
  )

  expect(result).toEqual({
    a : {
      0 : 's',
      1 : 't',
      2 : 'r',
      b : 42,
    },
  })
})

test('bug', () => {
  /*
    https://github.com/selfrefactor/rambda/issues/524
  */
  const state = {}

  const withDateLike = assocPath(
    [ 'outerProp', '2020-03-10' ],
    { prop : 2 },
    state
  )
  const withNumber = assocPath(
    [ 'outerProp', '5' ], { prop : 2 }, state
  )

  const withDateLikeExpected = { outerProp : { '2020-03-10' : { prop : 2 } } }
  const withNumberExpected = { outerProp : { 5 : { prop : 2 } } }
  expect(withDateLike).toEqual(withDateLikeExpected)
  expect(withNumber).toEqual(withNumberExpected)
})

test('adds a key to an empty object', () => {
  expect(assocPath(
    [ 'a' ], 1, {}
  )).toEqual({ a : 1 })
})

test('adds a key to a non-empty object', () => {
  expect(assocPath(
    'b', 2, { a : 1 }
  )).toEqual({
    a : 1,
    b : 2,
  })
})

test('adds a nested key to a non-empty object', () => {
  expect(assocPath(
    'b.c', 2, { a : 1 }
  )).toEqual({
    a : 1,
    b : { c : 2 },
  })
})

test('adds a nested key to a nested non-empty object - curry case 1', () => {
  expect(assocPath('b.d',
    3)({
    a : 1,
    b : { c : 2 },
  })).toEqual({
    a : 1,
    b : {
      c : 2,
      d : 3,
    },
  })
})

test('adds a key to a non-empty object - curry case 1', () => {
  expect(assocPath('b', 2)({ a : 1 })).toEqual({
    a : 1,
    b : 2,
  })
})

test('adds a nested key to a non-empty object - curry case 1', () => {
  expect(assocPath('b.c', 2)({ a : 1 })).toEqual({
    a : 1,
    b : { c : 2 },
  })
})

test('adds a key to a non-empty object - curry case 2', () => {
  expect(assocPath('b')(2, { a : 1 })).toEqual({
    a : 1,
    b : 2,
  })
})

test('adds a key to a non-empty object - curry case 3', () => {
  const result = assocPath('b')(2)({ a : 1 })

  expect(result).toEqual({
    a : 1,
    b : 2,
  })
})

test('changes an existing key', () => {
  expect(assocPath(
    'a', 2, { a : 1 }
  )).toEqual({ a : 2 })
})

test('undefined is considered an empty object', () => {
  expect(assocPath(
    'a', 1, undefined
  )).toEqual({ a : 1 })
})

test('null is considered an empty object', () => {
  expect(assocPath(
    'a', 1, null
  )).toEqual({ a : 1 })
})

test('value can be null', () => {
  expect(assocPath(
    'a', null, null
  )).toEqual({ a : null })
})

test('value can be undefined', () => {
  expect(assocPath(
    'a', undefined, null
  )).toEqual({ a : undefined })
})

test('assignment is shallow', () => {
  expect(assocPath(
    'a', { b : 2 }, { a : { c : 3 } }
  )).toEqual({ a : { b : 2 } })
})

test('empty array as path', () => {
  const result = assocPath(
    [], 3, {
      a : 1,
      b : 2,
    }
  )
  expect(result).toBe(3)
})

test('happy', () => {
  const expected = { foo : { bar : { baz : 42 } } }
  const result = assocPath(
    [ 'foo', 'bar', 'baz' ], 42, { foo : null }
  )
  expect(result).toEqual(expected)
})

import {assocPath} from 'rambda'

interface Output {
  a: number,
  foo: {bar: number},
}

describe('R.assocPath - user must explicitly set type of output', () => {
  it('with array as path input', () => {
    const result = assocPath<Output>(['foo', 'bar'], 2, {a: 1})

    result // $ExpectType Output
  })
  it('with string as path input', () => {
    const result = assocPath<Output>('foo.bar', 2, {a: 1})

    result // $ExpectType Output
  })
})

describe('R.assocPath - curried', () => {
  it('with array as path input', () => {
    const result = assocPath<Output>(['foo', 'bar'], 2)({a: 1})

    result // $ExpectType Output
  })
  it('with string as path input', () => {
    const result = assocPath<Output>('foo.bar', 2)({a: 1})

    result // $ExpectType Output
  })
})

binary

Try this R.binary example in Rambda REPL

bind


bind<F extends AnyFunction, T>(fn: F, thisObj: T): (...args: Parameters<F>) => ReturnType<F>

Creates a function that is bound to a context.

Try this R.bind example in Rambda REPL

bind<F extends AnyFunction, T>(fn: F, thisObj: T): (...args: Parameters<F>) => ReturnType<F>;
bind<F extends AnyFunction, T>(fn: F): (thisObj: T) => (...args: Parameters<F>) => ReturnType<F>;

import { curryN } from './curryN.js'

export function bind(fn, thisObj){
  if (arguments.length === 1){
    return _thisObj => bind(fn, _thisObj)
  }

  return curryN(fn.length, (...args) => fn.apply(thisObj, args))
}

import { bind } from './bind.js'

function Foo(x){
  this.x = x
}
function add(x){
  return this.x + x
}
function Bar(x, y){
  this.x = x
  this.y = y
}
Bar.prototype = new Foo()
Bar.prototype.getX = function (){
  return 'prototype getX'
}

test('returns a function', () => {
  expect(typeof bind(add)(Foo)).toBe('function')
})

test('returns a function bound to the specified context object', () => {
  const f = new Foo(12)
  function isFoo(){
    return this instanceof Foo
  }
  const isFooBound = bind(isFoo, f)
  expect(isFoo()).toBeFalse()
  expect(isFooBound()).toBeTrue()
})

test('works with built-in types', () => {
  const abc = bind(String.prototype.toLowerCase, 'ABCDEFG')
  expect(typeof abc).toBe('function')
  expect(abc()).toBe('abcdefg')
})

test('works with user-defined types', () => {
  const f = new Foo(12)
  function getX(){
    return this.x
  }
  const getXFooBound = bind(getX, f)
  expect(getXFooBound()).toBe(12)
})

test('works with plain objects', () => {
  const pojso = { x : 100 }
  function incThis(){
    return this.x + 1
  }
  const incPojso = bind(incThis, pojso)
  expect(typeof incPojso).toBe('function')
  expect(incPojso()).toBe(101)
})

test('does not interfere with existing object methods', () => {
  const b = new Bar('a', 'b')
  function getX(){
    return this.x
  }
  const getXBarBound = bind(getX, b)
  expect(b.getX()).toBe('prototype getX')
  expect(getXBarBound()).toBe('a')
})

test('preserves arity', () => {
  const f0 = function (){
    return 0
  }
  const f1 = function (a){
    return a
  }
  const f2 = function (a, b){
    return a + b
  }
  const f3 = function (
    a, b, c
  ){
    return a + b + c
  }

  expect(bind(f0, {})).toHaveLength(0)
  expect(bind(f1, {})).toHaveLength(1)
  expect(bind(f2, {})).toHaveLength(2)
  expect(bind(f3, {})).toHaveLength(3)
})

import {bind} from 'rambda'

class Foo {}
function isFoo<T = any>(this: T): boolean {
  return this instanceof Foo
}

describe('R.bind', () => {
  it('happy', () => {
    const foo = new Foo()
    const result = bind(isFoo, foo)()

    result // $ExpectType boolean
  })
})

both


both(pred1: Pred, pred2: Pred): Pred

It returns a function with input argument.

This function will return true, if both firstCondition and secondCondition return true when input is passed as their argument.

Try this R.both example in Rambda REPL

both(pred1: Pred, pred2: Pred): Pred;
both<T>(pred1: Predicate<T>, pred2: Predicate<T>): Predicate<T>;
both<T>(pred1: Predicate<T>): (pred2: Predicate<T>) => Predicate<T>;
both(pred1: Pred): (pred2: Pred) => Pred;

export function both(f, g){
  if (arguments.length === 1) return _g => both(f, _g)

  return (...input) => f(...input) && g(...input)
}

import { both } from './both.js'

const firstFn = val => val > 0
const secondFn = val => val < 10

test('with curry', () => {
  expect(both(firstFn)(secondFn)(17)).toBeFalse()
})

test('without curry', () => {
  expect(both(firstFn, secondFn)(7)).toBeTrue()
})

test('with multiple inputs', () => {
  const between = function (
    a, b, c
  ){
    return a < b && b < c
  }
  const total20 = function (
    a, b, c
  ){
    return a + b + c === 20
  }
  const fn = both(between, total20)
  expect(fn(
    5, 7, 8
  )).toBeTrue()
})

test('skip evaluation of the second expression', () => {
  let effect = 'not evaluated'
  const F = function (){
    return false
  }
  const Z = function (){
    effect = 'Z got evaluated'
  }
  both(F, Z)()

  expect(effect).toBe('not evaluated')
})

import {both} from 'rambda'

describe('R.both', () => {
  it('with passed type', () => {
    const fn = both<number>(
      x => x > 1,
      x => x % 2 === 0
    )
    fn // $ExpectType Predicate<number>
    const result = fn(2) // $ExpectType boolean
    result // $ExpectType boolean
  })
  it('with passed type - curried', () => {
    const fn = both<number>(x => x > 1)(x => x % 2 === 0)
    fn // $ExpectType Predicate<number>
    const result = fn(2)
    result // $ExpectType boolean
  })
  it('no type passed', () => {
    const fn = both(
      x => {
        x // $ExpectType any
        return x > 1
      },
      x => {
        x // $ExpectType any
        return x % 2 === 0
      }
    )
    const result = fn(2)
    result // $ExpectType boolean
  })
  it('no type passed - curried', () => {
    const fn = both((x: number) => {
      x // $ExpectType number
      return x > 1
    })((x: number) => {
      x // $ExpectType number
      return x % 2 === 0
    })
    const result = fn(2)
    result // $ExpectType boolean
  })
})

call

Try this R.call example in Rambda REPL

chain


chain<T, U>(fn: (n: T) => U[], list: T[]): U[]

The method is also known as flatMap.

Try this R.chain example in Rambda REPL

chain<T, U>(fn: (n: T) => U[], list: T[]): U[];
chain<T, U>(fn: (n: T) => U[]): (list: T[]) => U[];

export function chain(fn, list){
  if (arguments.length === 1){
    return _list => chain(fn, _list)
  }

  return [].concat(...list.map(fn))
}

import { chain as chainRamda } from 'ramda'

import { chain } from './chain.js'

const duplicate = n => [ n, n ]

test('happy', () => {
  const fn = x => [ x * 2 ]
  const list = [ 1, 2, 3 ]

  const result = chain(fn, list)

  expect(result).toEqual([ 2, 4, 6 ])
})

test('maps then flattens one level', () => {
  expect(chain(duplicate, [ 1, 2, 3 ])).toEqual([ 1, 1, 2, 2, 3, 3 ])
})

test('maps then flattens one level - curry', () => {
  expect(chain(duplicate)([ 1, 2, 3 ])).toEqual([ 1, 1, 2, 2, 3, 3 ])
})

test('flattens only one level', () => {
  const nest = n => [ [ n ] ]
  expect(chain(nest, [ 1, 2, 3 ])).toEqual([ [ 1 ], [ 2 ], [ 3 ] ])
})

test('can compose', () => {
  function dec(x){
    return [ x - 1 ]
  }
  function times2(x){
    return [ x * 2 ]
  }

  const mdouble = chain(times2)
  const mdec = chain(dec)
  expect(mdec(mdouble([ 10, 20, 30 ]))).toEqual([ 19, 39, 59 ])
})

test('@types/ramda broken test', () => {
  const score = {
    maths   : 90,
    physics : 80,
  }

  const calculateTotal = score => {
    const { maths, physics } = score

    return maths + physics
  }

  const assocTotalToScore = (total, score) => ({
    ...score,
    total,
  })

  const calculateAndAssocTotalToScore = chainRamda(assocTotalToScore,
    calculateTotal)
  expect(() =>
    calculateAndAssocTotalToScore(score)).toThrowErrorMatchingInlineSnapshot('"fn(...) is not a function"')
})

import {chain} from 'rambda'

const list = [1, 2, 3]
const fn = (x: number) => [`${x}`, `${x}`]

describe('R.chain', () => {
  it('without passing type', () => {
    const result = chain(fn, list)
    result // $ExpectType string[]

    const curriedResult = chain(fn)(list)
    curriedResult // $ExpectType string[]
  })
})

clamp

Restrict a number input to be within min and max limits.

If input is bigger than max, then the result is max.

If input is smaller than min, then the result is min.

Try this R.clamp example in Rambda REPL

clone

It creates a deep copy of the input, which may contain (nested) Arrays and Objects, Numbers, Strings, Booleans and Dates.

Try this R.clone example in Rambda REPL

collectBy

Try this R.collectBy example in Rambda REPL

comparator

It returns a comparator function that can be used in sort method.

Try this R.comparator example in Rambda REPL

complement

It returns inverted version of origin function that accept input as argument.

The return value of inverted is the negative boolean value of origin(input).

Try this R.complement example in Rambda REPL

compose

It performs right-to-left function composition.

Try this R.compose example in Rambda REPL

composeWith

Try this R.composeWith example in Rambda REPL

concat

It returns a new string or array, which is the result of merging x and y.

Try this R.concat example in Rambda REPL

cond

It takes list with conditions and returns a new function fn that expects input as argument.

This function will start evaluating the conditions in order to find the first winner(order of conditions matter).

The winner is this condition, which left side returns true when input is its argument. Then the evaluation of the right side of the winner will be the final result.

If no winner is found, then fn returns undefined.

Try this R.cond example in Rambda REPL

converge

Accepts a converging function and a list of branching functions and returns a new function. When invoked, this new function is applied to some arguments, each branching function is applied to those same arguments. The results of each branching function are passed as arguments to the converging function to produce the return value.

Try this R.converge example in Rambda REPL

count

It counts how many times predicate function returns true, when supplied with iteration of list.

Try this R.count example in Rambda REPL

countBy


countBy<T extends unknown>(transformFn: (x: T) => any, list: T[]): Record<string, number>

It counts elements in a list after each instance of the input list is passed through transformFn function.

Try this R.countBy example in Rambda REPL

countBy<T extends unknown>(transformFn: (x: T) => any, list: T[]): Record<string, number>;
countBy<T extends unknown>(transformFn: (x: T) => any): (list: T[]) => Record<string, number>;

export function countBy(fn, list){
  if (arguments.length === 1){
    return _list => countBy(fn, _list)
  }
  const willReturn = {}

  list.forEach(item => {
    const key = fn(item)
    if (!willReturn[ key ]){
      willReturn[ key ] = 1
    } else {
      willReturn[ key ]++
    }
  })

  return willReturn
}

import { countBy } from './countBy.js'

const list = [ 'a', 'A', 'b', 'B', 'c', 'C' ]

test('happy', () => {
  const result = countBy(x => x.toLowerCase(), list)
  expect(result).toEqual({
    a : 2,
    b : 2,
    c : 2,
  })
})

import {countBy} from 'rambda'

const transformFn = (x: string) => x.toLowerCase()
const list = ['a', 'A', 'b', 'B', 'c', 'C']

describe('R.countBy', () => {
  it('happy', () => {
    const result = countBy(transformFn, list)

    result // $ExpectType Record<string, number>
  })
  it('curried', () => {
    const result = countBy(transformFn)(list)

    result // $ExpectType Record<string, number>
  })
})

curry

It expects a function as input and returns its curried version.

Try this R.curry example in Rambda REPL

curryN

It returns a curried equivalent of the provided function, with the specified arity.

dec

It decrements a number.

Try this R.dec example in Rambda REPL

defaultTo


defaultTo<T>(defaultValue: T, input: T | null | undefined): T

It returns defaultValue, if all of inputArguments are undefined, null or NaN.

Else, it returns the first truthy inputArguments instance(from left to right).

Try this R.defaultTo example in Rambda REPL

defaultTo<T>(defaultValue: T, input: T | null | undefined): T;
defaultTo<T>(defaultValue: T): (input: T | null | undefined) => T;

function isFalsy(input){
  return (
    input === undefined || input === null || Number.isNaN(input) === true
  )
}

export function defaultTo(defaultArgument, input){
  if (arguments.length === 1){
    return _input => defaultTo(defaultArgument, _input)
  }

  return isFalsy(input) ? defaultArgument : input
}

import { defaultTo } from './defaultTo.js'

test('with undefined', () => {
  expect(defaultTo('foo')(undefined)).toBe('foo')
})

test('with null', () => {
  expect(defaultTo('foo')(null)).toBe('foo')
})

test('with NaN', () => {
  expect(defaultTo('foo')(NaN)).toBe('foo')
})

test('with empty string', () => {
  expect(defaultTo('foo', '')).toBe('')
})

test('with false', () => {
  expect(defaultTo('foo', false)).toBeFalse()
})

test('when inputArgument passes initial check', () => {
  expect(defaultTo('foo', 'bar')).toBe('bar')
})

import {defaultTo} from 'rambda'

describe('R.defaultTo with Ramda spec', () => {
  it('happy', () => {
    const result = defaultTo('foo', '')
    result // $ExpectType "" | "foo"
  })
  it('with explicit type', () => {
    const result = defaultTo<string>('foo', null)
    result // $ExpectType string
  })
})

descend

Try this R.descend example in Rambda REPL

difference


difference<T>(a: T[], b: T[]): T[]

It returns the uniq set of all elements in the first list a not contained in the second list b.

R.equals is used to determine equality.

Try this R.difference example in Rambda REPL

difference<T>(a: T[], b: T[]): T[];
difference<T>(a: T[]): (b: T[]) => T[];

import { includes } from './includes.js'
import { uniq } from './uniq.js'

export function difference(a, b){
  if (arguments.length === 1) return _b => difference(a, _b)

  return uniq(a).filter(aInstance => !includes(aInstance, b))
}

import { difference as differenceRamda } from 'ramda'

import { difference } from './difference.js'

test('difference', () => {
  const a = [ 1, 2, 3, 4 ]
  const b = [ 3, 4, 5, 6 ]
  expect(difference(a)(b)).toEqual([ 1, 2 ])

  expect(difference([], [])).toEqual([])
})

test('difference with objects', () => {
  const a = [ { id : 1 }, { id : 2 }, { id : 3 }, { id : 4 } ]
  const b = [ { id : 3 }, { id : 4 }, { id : 5 }, { id : 6 } ]
  expect(difference(a, b)).toEqual([ { id : 1 }, { id : 2 } ])
})

test('no duplicates in first list', () => {
  const M2 = [ 1, 2, 3, 4, 1, 2, 3, 4 ]
  const N2 = [ 3, 3, 4, 4, 5, 5, 6, 6 ]
  expect(difference(M2, N2)).toEqual([ 1, 2 ])
})

test('should use R.equals', () => {
  expect(difference([ 1 ], [ 1 ])).toHaveLength(0)
  expect(differenceRamda([ NaN ], [ NaN ])).toHaveLength(0)
})

import {difference} from 'rambda'

const list1 = [1, 2, 3]
const list2 = [1, 2, 4]

describe('R.difference', () => {
  it('happy', () => {
    const result = difference(list1, list2)

    result // $ExpectType number[]
  })
  it('curried', () => {
    const result = difference(list1)(list2)

    result // $ExpectType number[]
  })
})

differenceWith


differenceWith<T1, T2>(
  pred: (a: T1, b: T2) => boolean,
  list1: T1[],
  list2: T2[],
): T1[]

Try this R.differenceWith example in Rambda REPL

differenceWith<T1, T2>(
  pred: (a: T1, b: T2) => boolean,
  list1: T1[],
  list2: T2[],
): T1[];
differenceWith<T1, T2>(
  pred: (a: T1, b: T2) => boolean,
): (list1: T1[], list2: T2[]) => T1[];
differenceWith<T1, T2>(
  pred: (a: T1, b: T2) => boolean,
  list1: T1[],
): (list2: T2[]) => T1[];

import { curry } from './curry.js'
import { _indexOf } from './equals.js'

export function differenceWithFn(
  fn, a, b
){
  const willReturn = []
  const [ first, second ] = a.length > b.length ? [ a, b ] : [ b, a ]

  first.forEach(item => {
    const hasItem = second.some(secondItem => fn(item, secondItem))
    if (!hasItem && _indexOf(item, willReturn) === -1){
      willReturn.push(item)
    }
  })

  return willReturn
}

export const differenceWith = curry(differenceWithFn)

import { differenceWith } from './differenceWith.js'

test('happy', () => {
  const foo = [ { a : 1 }, { a : 2 }, { a : 3 } ]
  const bar = [ { a : 3 }, { a : 4 } ]
  const fn = function (r, s){
    return r.a === s.a
  }
  const result = differenceWith(
    fn, foo, bar
  )
  expect(result).toEqual([ { a : 1 }, { a : 2 } ])
})

dissoc

It returns a new object that does not contain property prop.

Try this R.dissoc example in Rambda REPL

dissocPath

Try this R.dissocPath example in Rambda REPL

divide

Try this R.divide example in Rambda REPL

drop


drop<T>(howMany: number, input: T[]): T[]

It returns howMany items dropped from beginning of list or string input.

Try this R.drop example in Rambda REPL

drop<T>(howMany: number, input: T[]): T[];
drop(howMany: number, input: string): string;
drop<T>(howMany: number): {
  <T>(input: T[]): T[];
  (input: string): string;
};

export function drop(howManyToDrop, listOrString){
  if (arguments.length === 1) return _list => drop(howManyToDrop, _list)

  return listOrString.slice(howManyToDrop > 0 ? howManyToDrop : 0)
}

import assert from 'assert'

import { drop } from './drop.js'

test('with array', () => {
  expect(drop(2)([ 'foo', 'bar', 'baz' ])).toEqual([ 'baz' ])
  expect(drop(3, [ 'foo', 'bar', 'baz' ])).toEqual([])
  expect(drop(4, [ 'foo', 'bar', 'baz' ])).toEqual([])
})

test('with string', () => {
  expect(drop(3, 'rambda')).toBe('bda')
})

test('with non-positive count', () => {
  expect(drop(0, [ 1, 2, 3 ])).toEqual([ 1, 2, 3 ])
  expect(drop(-1, [ 1, 2, 3 ])).toEqual([ 1, 2, 3 ])
  expect(drop(-Infinity, [ 1, 2, 3 ])).toEqual([ 1, 2, 3 ])
})

test('should return copy', () => {
  const xs = [ 1, 2, 3 ]

  assert.notStrictEqual(drop(0, xs), xs)
  assert.notStrictEqual(drop(-1, xs), xs)
})

import {drop} from 'rambda'

const list = [1, 2, 3, 4]
const str = 'foobar'
const howMany = 2

describe('R.drop - array', () => {
  it('happy', () => {
    const result = drop(howMany, list)
    result // $ExpectType number[]
  })
  it('curried', () => {
    const result = drop(howMany)(list)
    result // $ExpectType number[]
  })
})

describe('R.drop - string', () => {
  it('happy', () => {
    const result = drop(howMany, str)
    result // $ExpectType string
  })
  it('curried', () => {
    const result = drop(howMany)(str)
    result // $ExpectType string
  })
})

dropLast


dropLast<T>(howMany: number, input: T[]): T[]

It returns howMany items dropped from the end of list or string input.

Try this R.dropLast example in Rambda REPL

dropLast<T>(howMany: number, input: T[]): T[];
dropLast(howMany: number, input: string): string;
dropLast<T>(howMany: number): {
  <T>(input: T[]): T[];
  (input: string): string;
};

export function dropLast(howManyToDrop, listOrString){
  if (arguments.length === 1){
    return _listOrString => dropLast(howManyToDrop, _listOrString)
  }

  return howManyToDrop > 0 ?
    listOrString.slice(0, -howManyToDrop) :
    listOrString.slice()
}

import assert from 'assert'

import { dropLast } from './dropLast.js'

test('with array', () => {
  expect(dropLast(2)([ 'foo', 'bar', 'baz' ])).toEqual([ 'foo' ])
  expect(dropLast(3, [ 'foo', 'bar', 'baz' ])).toEqual([])
  expect(dropLast(4, [ 'foo', 'bar', 'baz' ])).toEqual([])
})

test('with string', () => {
  expect(dropLast(3, 'rambda')).toBe('ram')
})

test('with non-positive count', () => {
  expect(dropLast(0, [ 1, 2, 3 ])).toEqual([ 1, 2, 3 ])
  expect(dropLast(-1, [ 1, 2, 3 ])).toEqual([ 1, 2, 3 ])
  expect(dropLast(-Infinity, [ 1, 2, 3 ])).toEqual([ 1, 2, 3 ])
})

test('should return copy', () => {
  const xs = [ 1, 2, 3 ]

  assert.notStrictEqual(dropLast(0, xs), xs)
  assert.notStrictEqual(dropLast(-1, xs), xs)
})

import {dropLast} from 'rambda'

const list = [1, 2, 3, 4]
const str = 'foobar'
const howMany = 2

describe('R.dropLast - array', () => {
  it('happy', () => {
    const result = dropLast(howMany, list)
    result // $ExpectType number[]
  })
  it('curried', () => {
    const result = dropLast(howMany)(list)
    result // $ExpectType number[]
  })
})

describe('R.dropLast - string', () => {
  it('happy', () => {
    const result = dropLast(howMany, str)
    result // $ExpectType string
  })
  it('curried', () => {
    const result = dropLast(howMany)(str)
    result // $ExpectType string
  })
})

dropLastWhile

Try this R.dropLastWhile example in Rambda REPL

dropRepeats


dropRepeats<T>(list: T[]): T[]

It removes any successive duplicates according to R.equals.

Try this R.dropRepeats example in Rambda REPL

dropRepeats<T>(list: T[]): T[];

import { isArray } from './_internals/isArray.js'
import { equals } from './equals.js'

export function dropRepeats(list){
  if (!isArray(list)){
    throw new Error(`${ list } is not a list`)
  }

  const toReturn = []

  list.reduce((prev, current) => {
    if (!equals(prev, current)){
      toReturn.push(current)
    }

    return current
  }, undefined)

  return toReturn
}

import { dropRepeats as dropRepeatsRamda } from 'ramda'

import { compareCombinations } from './_internals/testUtils.js'
import { add } from './add.js'
import { dropRepeats } from './dropRepeats.js'

const list = [ 1, 2, 2, 2, 3, 4, 4, 5, 5, 3, 2, 2, { a : 1 }, { a : 1 } ]
const listClean = [ 1, 2, 3, 4, 5, 3, 2, { a : 1 } ]

test('happy', () => {
  const result = dropRepeats(list)
  expect(result).toEqual(listClean)
})

const possibleLists = [
  [ add(1), async () => {}, [ 1 ], [ 1 ], [ 2 ], [ 2 ] ],
  [ add(1), add(1), add(2) ],
  [],
  1,
  /foo/g,
  Promise.resolve(1),
]

describe('brute force', () => {
  compareCombinations({
    firstInput : possibleLists,
    callback   : errorsCounters => {
      expect(errorsCounters).toMatchInlineSnapshot(`
        {
          "ERRORS_MESSAGE_MISMATCH": 0,
          "ERRORS_TYPE_MISMATCH": 0,
          "RESULTS_MISMATCH": 1,
          "SHOULD_NOT_THROW": 3,
          "SHOULD_THROW": 0,
          "TOTAL_TESTS": 6,
        }
      `)
    },
    fn      : dropRepeats,
    fnRamda : dropRepeatsRamda,
  })
})

import {dropRepeats} from 'rambda'

describe('R.dropRepeats', () => {
  it('happy', () => {
    const result = dropRepeats([1, 2, 2, 3])

    result // $ExpectType number[]
  })
})

dropRepeatsBy

Try this R.dropRepeatsBy example in Rambda REPL

dropRepeatsWith

Try this R.dropRepeatsWith example in Rambda REPL

dropWhile

Try this R.dropWhile example in Rambda REPL

either


either(firstPredicate: Pred, secondPredicate: Pred): Pred

It returns a new predicate function from firstPredicate and secondPredicate inputs.

This predicate function will return true, if any of the two input predicates return true.

Try this R.either example in Rambda REPL

either(firstPredicate: Pred, secondPredicate: Pred): Pred;
either<T>(firstPredicate: Predicate<T>, secondPredicate: Predicate<T>): Predicate<T>;
either<T>(firstPredicate: Predicate<T>): (secondPredicate: Predicate<T>) => Predicate<T>;
either(firstPredicate: Pred): (secondPredicate: Pred) => Pred;

export function either(firstPredicate, secondPredicate){
  if (arguments.length === 1){
    return _secondPredicate => either(firstPredicate, _secondPredicate)
  }

  return (...input) =>
    Boolean(firstPredicate(...input) || secondPredicate(...input))
}

import { either } from './either.js'

test('with multiple inputs', () => {
  const between = function (
    a, b, c
  ){
    return a < b && b < c
  }
  const total20 = function (
    a, b, c
  ){
    return a + b + c === 20
  }
  const fn = either(between, total20)
  expect(fn(
    7, 8, 5
  )).toBeTrue()
})

test('skip evaluation of the second expression', () => {
  let effect = 'not evaluated'
  const F = function (){
    return true
  }
  const Z = function (){
    effect = 'Z got evaluated'
  }
  either(F, Z)()

  expect(effect).toBe('not evaluated')
})

test('case 1', () => {
  const firstFn = val => val > 0
  const secondFn = val => val * 5 > 10

  expect(either(firstFn, secondFn)(1)).toBeTrue()
})

test('case 2', () => {
  const firstFn = val => val > 0
  const secondFn = val => val === -10
  const fn = either(firstFn)(secondFn)

  expect(fn(-10)).toBeTrue()
})

import {either} from 'rambda'

describe('R.either', () => {
  it('with passed type', () => {
    const fn = either<number>(
      x => x > 1,
      x => x % 2 === 0
    )
    fn // $ExpectType Predicate<number>
    const result = fn(2) // $ExpectType boolean
    result // $ExpectType boolean
  })
  it('with passed type - curried', () => {
    const fn = either<number>(x => x > 1)(x => x % 2 === 0)
    fn // $ExpectType Predicate<number>
    const result = fn(2)
    result // $ExpectType boolean
  })
  it('no type passed', () => {
    const fn = either(
      x => {
        x // $ExpectType any
        return x > 1
      },
      x => {
        x // $ExpectType any
        return x % 2 === 0
      }
    )
    const result = fn(2)
    result // $ExpectType boolean
  })
  it('no type passed - curried', () => {
    const fn = either((x: number) => {
      x // $ExpectType number
      return x > 1
    })((x: number) => {
      x // $ExpectType number
      return x % 2 === 0
    })
    const result = fn(2)
    result // $ExpectType boolean
  })
})

empty

Try this R.empty example in Rambda REPL

endsWith


endsWith<T extends string>(question: T, str: string): boolean

When iterable is a string, then it behaves as String.prototype.endsWith. When iterable is a list, then it uses R.equals to determine if the target list ends in the same way as the given target.

Try this R.endsWith example in Rambda REPL

endsWith<T extends string>(question: T, str: string): boolean;
endsWith<T extends string>(question: T): (str: string) => boolean;
endsWith<T>(question: T[], list: T[]): boolean;
endsWith<T>(question: T[]): (list: T[]) => boolean;

import { isArray } from './_internals/isArray.js'
import { equals } from './equals.js'

export function endsWith(target, iterable){
  if (arguments.length === 1) return _iterable => endsWith(target, _iterable)

  if (typeof iterable === 'string'){
    return iterable.endsWith(target)
  }
  if (!isArray(target)) return false

  const diff = iterable.length - target.length
  let correct = true
  const filtered = target.filter((x, index) => {
    if (!correct) return false
    const result = equals(x, iterable[ index + diff ])
    if (!result) correct = false

    return result
  })

  return filtered.length === target.length
}

import { endsWith as endsWithRamda } from 'ramda'

import { compareCombinations } from './_internals/testUtils.js'
import { endsWith } from './endsWith.js'

test('with string', () => {
  expect(endsWith('bar', 'foo-bar')).toBeTrue()
  expect(endsWith('baz')('foo-bar')).toBeFalse()
})

test('use R.equals with array', () => {
  const list = [ { a : 1 }, { a : 2 }, { a : 3 } ]
  expect(endsWith({ a : 3 }, list)).toBeFalse(),
  expect(endsWith([ { a : 3 } ], list)).toBeTrue()
  expect(endsWith([ { a : 2 }, { a : 3 } ], list)).toBeTrue()
  expect(endsWith(list, list)).toBeTrue()
  expect(endsWith([ { a : 1 } ], list)).toBeFalse()
})

export const possibleTargets = [
  NaN,
  [ NaN ],
  /foo/,
  [ /foo/ ],
  Promise.resolve(1),
  [ Promise.resolve(1) ],
  Error('foo'),
  [ Error('foo') ],
]

export const possibleIterables = [
  [ Promise.resolve(1), Promise.resolve(2) ],
  [ /foo/, /bar/ ],
  [ NaN ],
  [ Error('foo'), Error('bar') ],
]

describe('brute force', () => {
  compareCombinations({
    fn          : endsWith,
    fnRamda     : endsWithRamda,
    firstInput  : possibleTargets,
    secondInput : possibleIterables,
    callback    : errorsCounters => {
      expect(errorsCounters).toMatchInlineSnapshot(`
        {
          "ERRORS_MESSAGE_MISMATCH": 0,
          "ERRORS_TYPE_MISMATCH": 0,
          "RESULTS_MISMATCH": 0,
          "SHOULD_NOT_THROW": 0,
          "SHOULD_THROW": 0,
          "TOTAL_TESTS": 32,
        }
      `)
    },
  })
})

import {endsWith} from 'rambda'

describe('R.endsWith - array', () => {
  const target = [{a: 2}]
  const input = [{a: 1}, {a: 2}]
  it('happy', () => {
    const result = endsWith(target, input)
    result // $ExpectType boolean
  })
  it('curried', () => {
    const result = endsWith(target)(input)
    result // $ExpectType boolean
  })
})

describe('R.endsWith - string', () => {
  const target = 'bar'
  const input = 'foo bar'
  it('happy', () => {
    const result = endsWith(target, input)
    result // $ExpectType boolean
  })
  it('curried', () => {
    const result = endsWith(target)(input)
    result // $ExpectType boolean
  })
})

eqBy

Try this R.eqBy example in Rambda REPL

eqProps

It returns true if property prop in obj1 is equal to property prop in obj2 according to R.equals.

Try this R.eqProps example in Rambda REPL

equals


equals<T>(x: T, y: T): boolean

It deeply compares x and y and returns true if they are equal.

Try this R.equals example in Rambda REPL

equals<T>(x: T, y: T): boolean;
equals<T>(x: T): (y: T) => boolean;

import { isArray } from './_internals/isArray.js'
import { type } from './type.js'

export function _lastIndexOf(valueToFind, list){
  if (!isArray(list))
    throw new Error(`Cannot read property 'indexOf' of ${ list }`)

  const typeOfValue = type(valueToFind)
  if (![ 'Array', 'NaN', 'Object', 'RegExp' ].includes(typeOfValue))
    return list.lastIndexOf(valueToFind)

  const { length } = list
  let index = length
  let foundIndex = -1

  while (--index > -1 && foundIndex === -1)
    if (equals(list[ index ], valueToFind))
      foundIndex = index

  return foundIndex
}

export function _indexOf(valueToFind, list){
  if (!isArray(list))
    throw new Error(`Cannot read property 'indexOf' of ${ list }`)

  const typeOfValue = type(valueToFind)
  if (![ 'Array', 'NaN', 'Object', 'RegExp' ].includes(typeOfValue))
    return list.indexOf(valueToFind)

  let index = -1
  let foundIndex = -1
  const { length } = list

  while (++index < length && foundIndex === -1)
    if (equals(list[ index ], valueToFind))
      foundIndex = index

  return foundIndex
}

function _arrayFromIterator(iter){
  const list = []
  let next
  while (!(next = iter.next()).done)
    list.push(next.value)

  return list
}

function _compareSets(a, b){
  if (a.size !== b.size)
    return false

  const aList = _arrayFromIterator(a.values())
  const bList = _arrayFromIterator(b.values())

  const filtered = aList.filter(aInstance => _indexOf(aInstance, bList) === -1)

  return filtered.length === 0
}

function compareErrors(a, b){
  if (a.message !== b.message) return false
  if (a.toString !== b.toString) return false

  return a.toString() === b.toString()
}

function parseDate(maybeDate){
  if (!maybeDate.toDateString) return [ false ]

  return [ true, maybeDate.getTime() ]
}

function parseRegex(maybeRegex){
  if (maybeRegex.constructor !== RegExp) return [ false ]

  return [ true, maybeRegex.toString() ]
}

export function equals(a, b){
  if (arguments.length === 1) return _b => equals(a, _b)

  if (Object.is(a, b)) return true

  const aType = type(a)

  if (aType !== type(b)) return false
  if (aType === 'Function')
    return a.name === undefined ? false : a.name === b.name

  if ([ 'NaN', 'Null', 'Undefined' ].includes(aType)) return true

  if ([ 'BigInt', 'Number' ].includes(aType)){
    if (Object.is(-0, a) !== Object.is(-0, b)) return false

    return a.toString() === b.toString()
  }

  if ([ 'Boolean', 'String' ].includes(aType))
    return a.toString() === b.toString()

  if (aType === 'Array'){
    const aClone = Array.from(a)
    const bClone = Array.from(b)

    if (aClone.toString() !== bClone.toString())
      return false

    let loopArrayFlag = true
    aClone.forEach((aCloneInstance, aCloneIndex) => {
      if (loopArrayFlag)
        if (
          aCloneInstance !== bClone[ aCloneIndex ] &&
          !equals(aCloneInstance, bClone[ aCloneIndex ])
        )
          loopArrayFlag = false

    })

    return loopArrayFlag
  }

  const aRegex = parseRegex(a)
  const bRegex = parseRegex(b)

  if (aRegex[ 0 ])
    return bRegex[ 0 ] ? aRegex[ 1 ] === bRegex[ 1 ] : false
  else if (bRegex[ 0 ]) return false

  const aDate = parseDate(a)
  const bDate = parseDate(b)

  if (aDate[ 0 ])
    return bDate[ 0 ] ? aDate[ 1 ] === bDate[ 1 ] : false
  else if (bDate[ 0 ]) return false

  if (a instanceof Error){
    if (!(b instanceof Error)) return false

    return compareErrors(a, b)
  }

  if (aType === 'Set')
    return _compareSets(a, b)

  if (aType === 'Object'){
    const aKeys = Object.keys(a)

    if (aKeys.length !== Object.keys(b).length)
      return false

    let loopObjectFlag = true
    aKeys.forEach(aKeyInstance => {
      if (loopObjectFlag){
        const aValue = a[ aKeyInstance ]
        const bValue = b[ aKeyInstance ]

        if (aValue !== bValue && !equals(aValue, bValue))
          loopObjectFlag = false

      }
    })

    return loopObjectFlag
  }

  return false
}

import { equals as equalsRamda } from 'ramda'

import { compareCombinations } from './_internals/testUtils.js'
import { variousTypes } from './benchmarks/_utils.js'
import { equals } from './equals.js'

test('compare functions', () => {
  function foo(){}
  function bar(){}
  const baz = () => {}

  const expectTrue = equals(foo, foo)
  const expectFalseFirst = equals(foo, bar)
  const expectFalseSecond = equals(foo, baz)

  expect(expectTrue).toBeTrue()
  expect(expectFalseFirst).toBeFalse()
  expect(expectFalseSecond).toBeFalse()
})

test('with array of objects', () => {
  const list1 = [ { a : 1 }, [ { b : 2 } ] ]
  const list2 = [ { a : 1 }, [ { b : 2 } ] ]
  const list3 = [ { a : 1 }, [ { b : 3 } ] ]

  expect(equals(list1, list2)).toBeTrue()
  expect(equals(list1, list3)).toBeFalse()
})

test('with regex', () => {
  expect(equals(/s/, /s/)).toBeTrue()
  expect(equals(/s/, /d/)).toBeFalse()
  expect(equals(/a/gi, /a/gi)).toBeTrue()
  expect(equals(/a/gim, /a/gim)).toBeTrue()
  expect(equals(/a/gi, /a/i)).toBeFalse()
})

test('not a number', () => {
  expect(equals([ NaN ], [ NaN ])).toBeTrue()
})

test('new number', () => {
  expect(equals(new Number(0), new Number(0))).toBeTrue()
  expect(equals(new Number(0), new Number(1))).toBeFalse()
  expect(equals(new Number(1), new Number(0))).toBeFalse()
})

test('new string', () => {
  expect(equals(new String(''), new String(''))).toBeTrue()
  expect(equals(new String(''), new String('x'))).toBeFalse()
  expect(equals(new String('x'), new String(''))).toBeFalse()
  expect(equals(new String('foo'), new String('foo'))).toBeTrue()
  expect(equals(new String('foo'), new String('bar'))).toBeFalse()
  expect(equals(new String('bar'), new String('foo'))).toBeFalse()
})

test('new Boolean', () => {
  expect(equals(new Boolean(true), new Boolean(true))).toBeTrue()
  expect(equals(new Boolean(false), new Boolean(false))).toBeTrue()
  expect(equals(new Boolean(true), new Boolean(false))).toBeFalse()
  expect(equals(new Boolean(false), new Boolean(true))).toBeFalse()
})

test('new Error', () => {
  expect(equals(new Error('XXX'), {})).toBeFalse()
  expect(equals(new Error('XXX'), new TypeError('XXX'))).toBeFalse()
  expect(equals(new Error('XXX'), new Error('YYY'))).toBeFalse()
  expect(equals(new Error('XXX'), new Error('XXX'))).toBeTrue()
  expect(equals(new Error('XXX'), new TypeError('YYY'))).toBeFalse()
  expect(equals(new Error('XXX'), new Error('XXX'))).toBeTrue()
})

test('with dates', () => {
  expect(equals(new Date(0), new Date(0))).toBeTrue()
  expect(equals(new Date(1), new Date(1))).toBeTrue()
  expect(equals(new Date(0), new Date(1))).toBeFalse()
  expect(equals(new Date(1), new Date(0))).toBeFalse()
  expect(equals(new Date(0), {})).toBeFalse()
  expect(equals({}, new Date(0))).toBeFalse()
})

test('ramda spec', () => {
  expect(equals({}, {})).toBeTrue()

  expect(equals({
    a : 1,
    b : 2,
  },
  {
    a : 1,
    b : 2,
  })).toBeTrue()

  expect(equals({
    a : 2,
    b : 3,
  },
  {
    a : 2,
    b : 3,
  })).toBeTrue()

  expect(equals({
    a : 2,
    b : 3,
  },
  {
    a : 3,
    b : 3,
  })).toBeFalse()

  expect(equals({
    a : 2,
    b : 3,
    c : 1,
  },
  {
    a : 2,
    b : 3,
  })).toBeFalse()
})

test('works with boolean tuple', () => {
  expect(equals([ true, false ], [ true, false ])).toBeTrue()
  expect(equals([ true, false ], [ true, true ])).toBeFalse()
})

test('works with equal objects within array', () => {
  const objFirst = {
    a : {
      b : 1,
      c : 2,
      d : [ 1 ],
    },
  }
  const objSecond = {
    a : {
      b : 1,
      c : 2,
      d : [ 1 ],
    },
  }

  const x = [ 1, 2, objFirst, null, '', [] ]
  const y = [ 1, 2, objSecond, null, '', [] ]
  expect(equals(x, y)).toBeTrue()
})

test('works with different objects within array', () => {
  const objFirst = { a : { b : 1 } }
  const objSecond = { a : { b : 2 } }

  const x = [ 1, 2, objFirst, null, '', [] ]
  const y = [ 1, 2, objSecond, null, '', [] ]
  expect(equals(x, y)).toBeFalse()
})

test('works with undefined as second argument', () => {
  expect(equals(1, undefined)).toBeFalse()

  expect(equals(undefined, undefined)).toBeTrue()
})

test('compare sets', () => {
  const toCompareDifferent = new Set([ { a : 1 }, { a : 2 } ])
  const toCompareSame = new Set([ { a : 1 }, { a : 2 }, { a : 1 } ])
  const testSet = new Set([ { a : 1 }, { a : 2 }, { a : 1 } ])
  expect(equals(toCompareSame, testSet)).toBeTruthy()
  expect(equals(toCompareDifferent, testSet)).toBeFalsy()
  expect(equalsRamda(toCompareSame, testSet)).toBeTruthy()
  expect(equalsRamda(toCompareDifferent, testSet)).toBeFalsy()
})

test('compare simple sets', () => {
  const testSet = new Set([ '2', '3', '3', '2', '1' ])
  expect(equals(new Set([ '3', '2', '1' ]), testSet)).toBeTruthy()
  expect(equals(new Set([ '3', '2', '0' ]), testSet)).toBeFalsy()
})

test('various examples', () => {
  expect(equals([ 1, 2, 3 ])([ 1, 2, 3 ])).toBeTrue()

  expect(equals([ 1, 2, 3 ], [ 1, 2 ])).toBeFalse()

  expect(equals(1, 1)).toBeTrue()

  expect(equals(1, '1')).toBeFalse()

  expect(equals({}, {})).toBeTrue()

  expect(equals({
    a : 1,
    b : 2,
  },
  {
    a : 1,
    b : 2,
  })).toBeTrue()

  expect(equals({
    a : 1,
    b : 2,
  },
  {
    a : 1,
    b : 1,
  })).toBeFalse()

  expect(equals({
    a : 1,
    b : false,
  },
  {
    a : 1,
    b : 1,
  })).toBeFalse()

  expect(equals({
    a : 1,
    b : 2,
  },
  {
    a : 1,
    b : 2,
    c : 3,
  })).toBeFalse()

  expect(equals({
    x : {
      a : 1,
      b : 2,
    },
  },
  {
    x : {
      a : 1,
      b : 2,
      c : 3,
    },
  })).toBeFalse()

  expect(equals({
    a : 1,
    b : 2,
  },
  {
    a : 1,
    b : 3,
  })).toBeFalse()

  expect(equals({ a : { b : { c : 1 } } }, { a : { b : { c : 1 } } })).toBeTrue()

  expect(equals({ a : { b : { c : 1 } } }, { a : { b : { c : 2 } } })).toBeFalse()

  expect(equals({ a : {} }, { a : {} })).toBeTrue()

  expect(equals('', '')).toBeTrue()

  expect(equals('foo', 'foo')).toBeTrue()

  expect(equals('foo', 'bar')).toBeFalse()

  expect(equals(0, false)).toBeFalse()

  expect(equals(/\s/g, null)).toBeFalse()

  expect(equals(null, null)).toBeTrue()

  expect(equals(false)(null)).toBeFalse()
})

test('with custom functions', () => {
  function foo(){
    return 1
  }
  foo.prototype.toString = () => ''
  const result = equals(foo, foo)

  expect(result).toBeTrue()
})

test('with classes', () => {
  class Foo{}
  const foo = new Foo()
  const result = equals(foo, foo)

  expect(result).toBeTrue()
})

test('with negative zero', () => {
  expect(equals(-0, -0)).toBeTrue()
  expect(equals(-0, 0)).toBeFalse()
  expect(equals(0, 0)).toBeTrue()
  expect(equals(-0, 1)).toBeFalse()
})

test('with big int', () => {
  const a = BigInt(9007199254740991)
  const b = BigInt(9007199254740991)
  const c = BigInt(7007199254740991)
  expect(equals(a, b)).toBeTrue()
  expect(equals(a, c)).toBeFalse()
})

describe('brute force', () => {
  compareCombinations({
    callback : errorsCounters => {
      expect(errorsCounters).toMatchInlineSnapshot(`
{
  "ERRORS_MESSAGE_MISMATCH": 0,
  "ERRORS_TYPE_MISMATCH": 0,
  "RESULTS_MISMATCH": 0,
  "SHOULD_NOT_THROW": 0,
  "SHOULD_THROW": 0,
  "TOTAL_TESTS": 289,
}
`)
    },
    firstInput  : variousTypes,
    fn          : equals,
    fnRamda     : equalsRamda,
    secondInput : variousTypes,
  })
})

import {equals} from 'rambda'

describe('R.equals', () => {
  it('happy', () => {
    const result = equals(4, 1)
    result // $ExpectType boolean
  })
  it('with object', () => {
    const foo = {a: 1}
    const bar = {a: 2}
    const result = equals(foo, bar)
    result // $ExpectType boolean
  })
  it('curried', () => {
    const result = equals(4)(1)

    result // $ExpectType boolean
  })
})

evolve


evolve<T, U>(rules: ((x: T) => U)[], list: T[]): U[]

It takes object or array of functions as set of rules. These rules are applied to the iterable input to produce the result.

Try this R.evolve example in Rambda REPL

evolve<T, U>(rules: ((x: T) => U)[], list: T[]): U[];
evolve<T, U>(rules: ((x: T) => U)[]) : (list: T[]) => U[];
evolve<E extends Evolver, V extends Evolvable<E>>(rules: E, obj: V): Evolve<V, E>;
evolve<E extends Evolver>(rules: E): <V extends Evolvable<E>>(obj: V) => Evolve<V, E>;

import { isArray } from './_internals/isArray.js'
import { mapArray, mapObject } from './map.js'
import { type } from './type.js'

export function evolveArray(rules, list){
  return mapArray(
    (x, i) => {
      if (type(rules[ i ]) === 'Function'){
        return rules[ i ](x)
      }

      return x
    },
    list,
    true
  )
}

export function evolveObject(rules, iterable){
  return mapObject((x, prop) => {
    if (type(x) === 'Object'){
      const typeRule = type(rules[ prop ])
      if (typeRule === 'Function'){
        return rules[ prop ](x)
      }
      if (typeRule === 'Object'){
        return evolve(rules[ prop ], x)
      }

      return x
    }
    if (type(rules[ prop ]) === 'Function'){
      return rules[ prop ](x)
    }

    return x
  }, iterable)
}

export function evolve(rules, iterable){
  if (arguments.length === 1){
    return _iterable => evolve(rules, _iterable)
  }
  const rulesType = type(rules)
  const iterableType = type(iterable)

  if (iterableType !== rulesType){
    throw new Error('iterableType !== rulesType')
  }

  if (![ 'Object', 'Array' ].includes(rulesType)){
    throw new Error(`'iterable' and 'rules' are from wrong type ${ rulesType }`)
  }

  if (iterableType === 'Object'){
    return evolveObject(rules, iterable)
  }

  return evolveArray(rules, iterable)
}

import { evolve as evolveRamda } from 'ramda'

import { add } from '../rambda.js'
import { compareCombinations, compareToRamda } from './_internals/testUtils.js'
import { evolve } from './evolve.js'

test('happy', () => {
  const rules = {
    foo    : add(1),
    nested : { bar : x => Object.keys(x).length },
  }
  const input = {
    a      : 1,
    foo    : 2,
    nested : { bar : { z : 3 } },
  }
  const result = evolve(rules, input)
  expect(result).toEqual({
    a      : 1,
    foo    : 3,
    nested : { bar : 1 },
  })
})

test('nested rule is wrong', () => {
  const rules = {
    foo    : add(1),
    nested : { bar : 10 },
  }
  const input = {
    a      : 1,
    foo    : 2,
    nested : { bar : { z : 3 } },
  }
  const result = evolve(rules)(input)
  expect(result).toEqual({
    a      : 1,
    foo    : 3,
    nested : { bar : { z : 3 } },
  })
})

test('is recursive', () => {
  const rules = {
    nested : {
      second : add(-1),
      third  : add(1),
    },
  }
  const object = {
    first  : 1,
    nested : {
      second : 2,
      third  : 3,
    },
  }
  const expected = {
    first  : 1,
    nested : {
      second : 1,
      third  : 4,
    },
  }
  const result = evolve(rules, object)
  expect(result).toEqual(expected)
})

test('ignores primitive values', () => {
  const rules = {
    n : 2,
    m : 'foo',
  }
  const object = {
    n : 0,
    m : 1,
  }
  const expected = {
    n : 0,
    m : 1,
  }
  const result = evolve(rules, object)
  expect(result).toEqual(expected)
})

test('with array', () => {
  const rules = [ add(1), add(-1) ]
  const list = [ 100, 1400 ]
  const expected = [ 101, 1399 ]
  const result = evolve(rules, list)
  expect(result).toEqual(expected)
})

const rulesObject = { a : add(1) }
const rulesList = [ add(1) ]
const possibleIterables = [ null, undefined, '', 42, [], [ 1 ], { a : 1 } ]
const possibleRules = [ ...possibleIterables, rulesList, rulesObject ]

describe('brute force', () => {
  compareCombinations({
    firstInput : possibleRules,
    callback   : errorsCounters => {
      expect(errorsCounters).toMatchInlineSnapshot(`
        {
          "ERRORS_MESSAGE_MISMATCH": 0,
          "ERRORS_TYPE_MISMATCH": 4,
          "RESULTS_MISMATCH": 0,
          "SHOULD_NOT_THROW": 51,
          "SHOULD_THROW": 0,
          "TOTAL_TESTS": 63,
        }
      `)
    },
    secondInput : possibleIterables,
    fn          : evolve,
    fnRamda     : evolveRamda,
  })
})

import {evolve, add} from 'rambda'

describe('R.evolve', () => {
  it('happy', () => {
    const input = {
      foo: 2,
      nested: {
        a: 1,
        bar: 3,
      },
    }
    const rules = {
      foo: add(1),
      nested: {
        a: add(-1),
        bar: add(1),
      },
    }
    const result = evolve(rules, input)
    const curriedResult = evolve(rules)(input)

    result.nested.a // $ExpectType number
    curriedResult.nested.a // $ExpectType number
    result.nested.bar // $ExpectType number
    result.foo // $ExpectType number
  })
  it('with array', () => {
    const rules = [String, String]
    const input = [100, 1400]
    const result = evolve(rules, input)
    const curriedResult = evolve(rules)(input)
    result // $ExpectType string[]
    curriedResult // $ExpectType string[]
  })
})

F


F(): boolean

Try this R.F example in Rambda REPL

F(): boolean;

export function F(){
  return false
}

filter


filter<T>(predicate: Predicate<T>): (input: T[]) => T[]

It filters list or object input using a predicate function.

Try this R.filter example in Rambda REPL

filter<T>(predicate: Predicate<T>): (input: T[]) => T[];
filter<T>(predicate: Predicate<T>, input: T[]): T[];
filter<T, U>(predicate: ObjectPredicate<T>): (x: Dictionary<T>) => Dictionary<T>;
filter<T>(predicate: ObjectPredicate<T>, x: Dictionary<T>): Dictionary<T>;

import { isArray } from './_internals/isArray.js'

export function filterObject(predicate, obj){
  const willReturn = {}

  for (const prop in obj){
    if (predicate(
      obj[ prop ], prop, obj
    )){
      willReturn[ prop ] = obj[ prop ]
    }
  }

  return willReturn
}

export function filterArray(
  predicate, list, indexed = false
){
  let index = 0
  const len = list.length
  const willReturn = []

  while (index < len){
    const predicateResult = indexed ?
      predicate(list[ index ], index) :
      predicate(list[ index ])
    if (predicateResult){
      willReturn.push(list[ index ])
    }

    index++
  }

  return willReturn
}

export function filter(predicate, iterable){
  if (arguments.length === 1)
    return _iterable => filter(predicate, _iterable)
  if (!iterable){
    throw new Error('Incorrect iterable input')
  }

  if (isArray(iterable)) return filterArray(
    predicate, iterable, false
  )

  return filterObject(predicate, iterable)
}

import { filter as filterRamda } from 'ramda'

import { filter } from './filter.js'
import { T } from './T.js'

const sampleObject = {
  a : 1,
  b : 2,
  c : 3,
  d : 4,
}

test('happy', () => {
  const isEven = n => n % 2 === 0

  expect(filter(isEven, [ 1, 2, 3, 4 ])).toEqual([ 2, 4 ])
  expect(filter(isEven, {
    a : 1,
    b : 2,
    d : 3,
  })).toEqual({ b : 2 })
})

test('predicate when input is object', () => {
  const obj = {
    a : 1,
    b : 2,
  }
  const predicate = (
    val, prop, inputObject
  ) => {
    expect(inputObject).toEqual(obj)
    expect(typeof prop).toBe('string')

    return val < 2
  }
  expect(filter(predicate, obj)).toEqual({ a : 1 })
})

test('with object', () => {
  const isEven = n => n % 2 === 0
  const result = filter(isEven, sampleObject)
  const expectedResult = {
    b : 2,
    d : 4,
  }

  expect(result).toEqual(expectedResult)
})

test('bad inputs difference between Ramda and Rambda', () => {
  expect(() => filter(T, null)).toThrowWithMessage(Error,
    'Incorrect iterable input')
  expect(() => filter(T)(undefined)).toThrowWithMessage(Error,
    'Incorrect iterable input')
  expect(() => filterRamda(T, null)).toThrowWithMessage(TypeError,
    'Cannot read properties of null (reading \'fantasy-land/filter\')')
  expect(() => filterRamda(T, undefined)).toThrowWithMessage(TypeError,
    'Cannot read properties of undefined (reading \'fantasy-land/filter\')')
})

import {filter} from 'rambda'

const list = [1, 2, 3]
const obj = {a: 1, b: 2}

describe('R.filter with array', () => {
  it('happy', () => {
    const result = filter<number>(x => {
      x // $ExpectType number
      return x > 1
    }, list)
    result // $ExpectType number[]
  })
  it('curried', () => {
    const result = filter<number>(x => {
      x // $ExpectType number
      return x > 1
    })(list)
    result // $ExpectType number[]
  })
})

describe('R.filter with objects', () => {
  it('happy', () => {
    const result = filter<number>((val, prop, origin) => {
      val // $ExpectType number
      prop // $ExpectType string
      origin // $ExpectType Dictionary<number>

      return val > 1
    }, obj)
    result // $ExpectType Dictionary<number>
  })
  it('curried version requires second dummy type', () => {
    const result = filter<number, any>((val, prop, origin) => {
      val // $ExpectType number
      prop // $ExpectType string
      origin // $ExpectType Dictionary<number>

      return val > 1
    })(obj)
    result // $ExpectType Dictionary<number>
  })
})

find


find<T>(predicate: (x: T) => boolean, list: T[]): T | undefined

It returns the first element of list that satisfy the predicate.

If there is no such element, it returns undefined.

Try this R.find example in Rambda REPL

find<T>(predicate: (x: T) => boolean, list: T[]): T | undefined;
find<T>(predicate: (x: T) => boolean): (list: T[]) => T | undefined;

export function find(predicate, list){
  if (arguments.length === 1) return _list => find(predicate, _list)

  let index = 0
  const len = list.length

  while (index < len){
    const x = list[ index ]
    if (predicate(x)){
      return x
    }

    index++
  }
}

import { find } from './find.js'
import { propEq } from './propEq.js'

const list = [ { a : 1 }, { a : 2 }, { a : 3 } ]

test('happy', () => {
  const fn = propEq(2, 'a')
  expect(find(fn, list)).toEqual({ a : 2 })
})

test('with curry', () => {
  const fn = propEq(4, 'a')
  expect(find(fn)(list)).toBeUndefined()
})

test('with empty list', () => {
  expect(find(() => true, [])).toBeUndefined()
})

import {find} from 'rambda'

const list = [1, 2, 3]

describe('R.find', () => {
  it('happy', () => {
    const predicate = (x: number) => x > 2
    const result = find(predicate, list)
    result // $ExpectType number | undefined
  })
  it('curried', () => {
    const predicate = (x: number) => x > 2
    const result = find(predicate)(list)
    result // $ExpectType number | undefined
  })
})

findIndex


findIndex<T>(predicate: (x: T) => boolean, list: T[]): number

It returns the index of the first element of list satisfying the predicate function.

If there is no such element, then -1 is returned.

Try this R.findIndex example in Rambda REPL

findIndex<T>(predicate: (x: T) => boolean, list: T[]): number;
findIndex<T>(predicate: (x: T) => boolean): (list: T[]) => number;

export function findIndex(predicate, list){
  if (arguments.length === 1) return _list => findIndex(predicate, _list)

  const len = list.length
  let index = -1

  while (++index < len){
    if (predicate(list[ index ])){
      return index
    }
  }

  return -1
}

import { findIndex } from './findIndex.js'
import { propEq } from './propEq.js'

const list = [ { a : 1 }, { a : 2 }, { a : 3 } ]

test('happy', () => {
  expect(findIndex(propEq(2, 'a'), list)).toBe(1)
  expect(findIndex(propEq(1, 'a'))(list)).toBe(0)
  expect(findIndex(propEq(4, 'a'))(list)).toBe(-1)
})

import {findIndex} from 'rambda'

const list = [1, 2, 3]

describe('R.findIndex', () => {
  it('happy', () => {
    const predicate = (x: number) => x > 2
    const result = findIndex(predicate, list)
    result // $ExpectType number
  })
  it('curried', () => {
    const predicate = (x: number) => x > 2
    const result = findIndex(predicate)(list)
    result // $ExpectType number
  })
})

findLast


findLast<T>(fn: (x: T) => boolean, list: T[]): T | undefined

It returns the last element of list satisfying the predicate function.

If there is no such element, then undefined is returned.

Try this R.findLast example in Rambda REPL

findLast<T>(fn: (x: T) => boolean, list: T[]): T | undefined;
findLast<T>(fn: (x: T) => boolean): (list: T[]) => T | undefined;

export function findLast(predicate, list){
  if (arguments.length === 1) return _list => findLast(predicate, _list)

  let index = list.length

  while (--index >= 0){
    if (predicate(list[ index ])){
      return list[ index ]
    }
  }

  return undefined
}

import { findLast } from './findLast.js'

test('happy', () => {
  const result = findLast(x => x > 1, [ 1, 1, 1, 2, 3, 4, 1 ])
  expect(result).toBe(4)

  expect(findLast(x => x === 0, [ 0, 1, 1, 2, 3, 4, 1 ])).toBe(0)
})

test('with curry', () => {
  expect(findLast(x => x > 1)([ 1, 1, 1, 2, 3, 4, 1 ])).toBe(4)
})

const obj1 = { x : 100 }
const obj2 = { x : 200 }
const a = [ 11, 10, 9, 'cow', obj1, 8, 7, 100, 200, 300, obj2, 4, 3, 2, 1, 0 ]
const even = function (x){
  return x % 2 === 0
}
const gt100 = function (x){
  return x > 100
}
const isStr = function (x){
  return typeof x === 'string'
}
const xGt100 = function (o){
  return o && o.x > 100
}

test('ramda 1', () => {
  expect(findLast(even, a)).toBe(0)
  expect(findLast(gt100, a)).toBe(300)
  expect(findLast(isStr, a)).toBe('cow')
  expect(findLast(xGt100, a)).toEqual(obj2)
})

test('ramda 2', () => {
  expect(findLast(even, [ 'zing' ])).toBeUndefined()
})

test('ramda 3', () => {
  expect(findLast(even, [ 2, 3, 5 ])).toBe(2)
})

test('ramda 4', () => {
  expect(findLast(even, [])).toBeUndefined()
})

import {findLast} from 'rambda'

const list = [1, 2, 3]

describe('R.findLast', () => {
  it('happy', () => {
    const predicate = (x: number) => x > 2
    const result = findLast(predicate, list)
    result // $ExpectType number | undefined
  })
  it('curried', () => {
    const predicate = (x: number) => x > 2
    const result = findLast(predicate)(list)
    result // $ExpectType number | undefined
  })
})

findLastIndex


findLastIndex<T>(predicate: (x: T) => boolean, list: T[]): number

It returns the index of the last element of list satisfying the predicate function.

If there is no such element, then -1 is returned.

Try this R.findLastIndex example in Rambda REPL

findLastIndex<T>(predicate: (x: T) => boolean, list: T[]): number;
findLastIndex<T>(predicate: (x: T) => boolean): (list: T[]) => number;

export function findLastIndex(fn, list){
  if (arguments.length === 1) return _list => findLastIndex(fn, _list)

  let index = list.length

  while (--index >= 0){
    if (fn(list[ index ])){
      return index
    }
  }

  return -1
}

import { findLastIndex } from './findLastIndex.js'

test('happy', () => {
  const result = findLastIndex(x => x > 1, [ 1, 1, 1, 2, 3, 4, 1 ])

  expect(result).toBe(5)

  expect(findLastIndex(x => x === 0, [ 0, 1, 1, 2, 3, 4, 1 ])).toBe(0)
})

test('with curry', () => {
  expect(findLastIndex(x => x > 1)([ 1, 1, 1, 2, 3, 4, 1 ])).toBe(5)
})

const obj1 = { x : 100 }
const obj2 = { x : 200 }
const a = [ 11, 10, 9, 'cow', obj1, 8, 7, 100, 200, 300, obj2, 4, 3, 2, 1, 0 ]
const even = function (x){
  return x % 2 === 0
}
const gt100 = function (x){
  return x > 100
}
const isStr = function (x){
  return typeof x === 'string'
}
const xGt100 = function (o){
  return o && o.x > 100
}

test('ramda 1', () => {
  expect(findLastIndex(even, a)).toBe(15)
  expect(findLastIndex(gt100, a)).toBe(9)
  expect(findLastIndex(isStr, a)).toBe(3)
  expect(findLastIndex(xGt100, a)).toBe(10)
})

test('ramda 2', () => {
  expect(findLastIndex(even, [ 'zing' ])).toBe(-1)
})

test('ramda 3', () => {
  expect(findLastIndex(even, [ 2, 3, 5 ])).toBe(0)
})

test('ramda 4', () => {
  expect(findLastIndex(even, [])).toBe(-1)
})

import {findLastIndex} from 'rambda'

const list = [1, 2, 3]

describe('R.findLastIndex', () => {
  it('happy', () => {
    const predicate = (x: number) => x > 2
    const result = findLastIndex(predicate, list)
    result // $ExpectType number
  })
  it('curried', () => {
    const predicate = (x: number) => x > 2
    const result = findLastIndex(predicate)(list)
    result // $ExpectType number
  })
})

flatten


flatten<T>(list: any[]): T[]

It deeply flattens an array.

Try this R.flatten example in Rambda REPL

flatten<T>(list: any[]): T[];

import { isArray } from './_internals/isArray.js'

export function flatten(list, input){
  const willReturn = input === undefined ? [] : input

  for (let i = 0; i < list.length; i++){
    if (isArray(list[ i ])){
      flatten(list[ i ], willReturn)
    } else {
      willReturn.push(list[ i ])
    }
  }

  return willReturn
}

import { flatten } from './flatten.js'

test('happy', () => {
  expect(flatten([ 1, 2, 3, [ [ [ [ [ 4 ] ] ] ] ] ])).toEqual([ 1, 2, 3, 4 ])

  expect(flatten([ 1, [ 2, [ [ 3 ] ] ], [ 4 ] ])).toEqual([ 1, 2, 3, 4 ])

  expect(flatten([ 1, [ 2, [ [ [ 3 ] ] ] ], [ 4 ] ])).toEqual([ 1, 2, 3, 4 ])

  expect(flatten([ 1, 2, [ 3, 4 ], 5, [ 6, [ 7, 8, [ 9, [ 10, 11 ], 12 ] ] ] ])).toEqual([ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 ])
})

test('readme example', () => {
  const result = flatten([ 1, 2, [ 3, 30, [ 300 ] ], [ 4 ] ])
  expect(result).toEqual([ 1, 2, 3, 30, 300, 4 ])
})

import {flatten} from 'rambda'

describe('flatten', () => {
  it('happy', () => {
    const result = flatten<number>([1, 2, [3, [4]]])
    result // $ExpectType number[]
  })
})

flip

It returns function which calls fn with exchanged first and second argument.

Try this R.flip example in Rambda REPL

forEach


forEach<T>(fn: Iterator<T, void>, list: T[]): T[]

It applies iterable function over all members of list and returns list.

Try this R.forEach example in Rambda REPL

forEach<T>(fn: Iterator<T, void>, list: T[]): T[];
forEach<T>(fn: Iterator<T, void>): (list: T[]) => T[];
forEach<T>(fn: ObjectIterator<T, void>, list: Dictionary<T>): Dictionary<T>;
forEach<T, U>(fn: ObjectIterator<T, void>): (list: Dictionary<T>) => Dictionary<T>;

import { isArray } from './_internals/isArray.js'
import { forEachObjIndexedFn } from './forEachObjIndexed.js'

export function forEach(fn, iterable){
  if (arguments.length === 1) return _list => forEach(fn, _list)
  if (iterable === undefined) return

  if (isArray(iterable)){
    let index = 0
    const len = iterable.length

    while (index < len){
      fn(iterable[ index ])
      index++
    }
  } else return forEachObjIndexedFn(fn, iterable)

  return iterable
}

import { forEach } from './forEach.js'
import { type } from './type.js'

test('happy', () => {
  const sideEffect = {}
  forEach(x => sideEffect[ `foo${ x }` ] = x + 10)([ 1, 2 ])

  expect(sideEffect).toEqual({
    foo1 : 11,
    foo2 : 12,
  })
})

test('iterate over object', () => {
  const obj = {
    a : 1,
    b : [ 1, 2 ],
    c : { d : 7 },
    f : 'foo',
  }
  const result = {}
  const returned = forEach((
    val, prop, inputObj
  ) => {
    expect(type(inputObj)).toBe('Object')
    result[ prop ] = `${ prop }-${ type(val) }`
  })(obj)

  const expected = {
    a : 'a-Number',
    b : 'b-Array',
    c : 'c-Object',
    f : 'f-String',
  }

  expect(result).toEqual(expected)
  expect(returned).toEqual(obj)
})

test('with empty list', () => {
  const list = []
  const result = forEach(x => x * x)(list)

  expect(result).toEqual(list)
})

test('with wrong input', () => {
  const list = undefined
  const result = forEach(x => x * x)(list)

  expect(result).toBeUndefined()
})

test('returns the input', () => {
  const list = [ 1, 2, 3 ]
  const result = forEach(x => x * x)(list)

  expect(result).toEqual(list)
})

import {forEach} from 'rambda'

const list = [1, 2, 3]
const obj = {a: 1, b: 2}

describe('R.forEach with arrays', () => {
  it('happy', () => {
    const result = forEach(a => {
      a // $ExpectType number
    }, list)
    result // $ExpectType number[]
  })
  it('curried require an explicit typing', () => {
    const result = forEach<number>(a => {
      a // $ExpectType number
    })(list)
    result // $ExpectType number[]
  })
})

describe('R.forEach with objects', () => {
  it('happy', () => {
    const result = forEach((a, b, c) => {
      a // $ExpectType number
      b // $ExpectType string
      c // $ExpectType Dictionary<number>
      return `${a}`
    }, obj)
    result // $ExpectType Dictionary<number>
  })
  it('curried require an input typing and a dummy third typing', () => {
    // Required in order all typings to work
    const result = forEach<number, any>((a, b, c) => {
      a // $ExpectType number
      b // $ExpectType string
      c // $ExpectType Dictionary<number>
    })(obj)
    result // $ExpectType Dictionary<number>
  })
  it('iterator without property', () => {
    const result = forEach(a => {
      a // $ExpectType number
    }, obj)
    result // $ExpectType Dictionary<number>
  })
})

forEachObjIndexed

fromPairs

It transforms a listOfPairs to an object.

Try this R.fromPairs example in Rambda REPL

groupBy

It splits list according to a provided groupFn function and returns an object.

Try this R.groupBy example in Rambda REPL

groupWith

It returns separated version of list or string input, where separation is done with equality compareFn function.

Try this R.groupWith example in Rambda REPL

gt

Try this R.gt example in Rambda REPL

gte

Try this R.gte example in Rambda REPL

has


has<T>(prop: string, obj: T): boolean

It returns true if obj has property prop.

Try this R.has example in Rambda REPL

has<T>(prop: string, obj: T): boolean;
has(prop: string): <T>(obj: T) => boolean;

export function has(prop, obj){
  if (arguments.length === 1) return _obj => has(prop, _obj)

  if (!obj) return false

  return obj.hasOwnProperty(prop)
}

import { has } from './has.js'

test('happy', () => {
  expect(has('a')({ a : 1 })).toBeTrue()
  expect(has('b', { a : 1 })).toBeFalse()
})

test('with non-object', () => {
  expect(has('a', undefined)).toBeFalse()
  expect(has('a', null)).toBeFalse()
  expect(has('a', true)).toBeFalse()
  expect(has('a', '')).toBeFalse()
  expect(has('a', /a/)).toBeFalse()
})

import {has} from 'rambda'

describe('R.has', () => {
  it('happy', () => {
    const result = has('foo', {a: 1})
    const curriedResult = has('bar')({a: 1})
    result // $ExpectType boolean
    curriedResult // $ExpectType boolean
  })
})

hasIn

Try this R.hasIn example in Rambda REPL

hasPath


hasPath<T>(
  path: string | string[],
  input: object
): boolean

It will return true, if input object has truthy path(calculated with R.path).

Try this R.hasPath example in Rambda REPL

hasPath<T>(
  path: string | string[],
  input: object
): boolean;
hasPath<T>(
  path: string | string[]
): (input: object) => boolean;

import { path } from './path.js'

export function hasPath(pathInput, obj){
  if (arguments.length === 1){
    return objHolder => hasPath(pathInput, objHolder)
  }

  return path(pathInput, obj) !== undefined
}

import { hasPath } from './hasPath.js'

test('when true', () => {
  const path = 'a.b'
  const obj = { a : { b : [] } }

  const result = hasPath(path)(obj)
  const expectedResult = true

  expect(result).toEqual(expectedResult)
})

test('when false', () => {
  const path = 'a.b'
  const obj = {}

  const result = hasPath(path, obj)
  const expectedResult = false

  expect(result).toEqual(expectedResult)
})

import {hasPath} from 'rambda'

describe('R.hasPath', () => {
  it('string path', () => {
    const obj = {a: {b: 1}}
    const result = hasPath('a.b', obj)
    const curriedResult = hasPath('a.c')(obj)
    result // $ExpectType boolean
    curriedResult // $ExpectType boolean
  })
  it('array path', () => {
    const obj = {a: {b: 1}}
    const result = hasPath(['a', 'b'], obj)
    const curriedResult = hasPath(['a', 'c'])(obj)
    result // $ExpectType boolean
    curriedResult // $ExpectType boolean
  })
})

head


head(str: string): string

It returns the first element of list or string input. It returns undefined if array has length of 0.

Try this R.head example in Rambda REPL

head(str: string): string;
head(str: ''): undefined;
head(list: readonly[]): undefined;
head<T>(list: never[]): undefined;
head<T extends unknown[]>(array: T): FirstArrayElement<T>
head<T extends readonly unknown[]>(array: T): FirstArrayElement<T>

export function head(listOrString){
  if (typeof listOrString === 'string') return listOrString[ 0 ] || ''

  return listOrString[ 0 ]
}

import { head } from './head.js'

test('head', () => {
  expect(head([ 'fi', 'fo', 'fum' ])).toBe('fi')
  expect(head([])).toBeUndefined()
  expect(head('foo')).toBe('f')
  expect(head('')).toBe('')
})

import {
  emptyList,
  emptyString,
  mixedList,
  mixedListConst,
  numberList,
  numberListConst,
  string,
} from '_internals/typescriptTestUtils'
import {head, last} from 'rambda'

describe('R.head', () => {
  it('string', () => {
    head(string) // $ExpectType string
    last(string) // $ExpectType string
  })
  it('empty string', () => {
    head(emptyString) // $ExpectType undefined
    last(emptyString) // $ExpectType undefined
  })
  it('array', () => {
    head(numberList) // $ExpectType number
    head(numberListConst) // $ExpectType 1

    last(numberList) // $ExpectType number
    last(numberListConst) // $ExpectType 3
  })
  it('empty array', () => {
    const list = [] as const
    head(emptyList) // $ExpectType undefined
    head(list) // $ExpectType undefined
    last(emptyList) // $ExpectType undefined
    last(list) // $ExpectType undefined
  })

  it('mixed', () => {
    head(mixedList) // $ExpectType string | number
    head(mixedListConst) // $ExpectType 1
    last(mixedList) // $ExpectType string | number
    last(mixedListConst) // $ExpectType "bar"
  })
})

identical

It returns true if its arguments a and b are identical.

Otherwise, it returns false.

Try this R.identical example in Rambda REPL

identity


identity<T>(input: T): T

It just passes back the supplied input argument.

Try this R.identity example in Rambda REPL

identity<T>(input: T): T;

export function identity(x){
  return x
}

import { identity } from './identity.js'

test('happy', () => {
  expect(identity(7)).toBe(7)
  expect(identity(true)).toBeTrue()
  expect(identity({ a : 1 })).toEqual({ a : 1 })
})

import {identity} from 'rambda'

describe('R.identity', () => {
  it('happy', () => {
    const result = identity(4)
    result // $ExpectType 4
  })
})

ifElse


ifElse<T, TFiltered extends T, TOnTrueResult, TOnFalseResult>(
  pred: (a: T) => a is TFiltered,
  onTrue: (a: TFiltered) => TOnTrueResult,
  onFalse: (a: Exclude<T, TFiltered>) => TOnFalseResult,
): (a: T) => TOnTrueResult | TOnFalseResult

It expects condition, onTrue and onFalse functions as inputs and it returns a new function with example name of fn.

When fn`` is called with inputargument, it will return eitheronTrue(input)oronFalse(input)depending oncondition(input)` evaluation.

Try this R.ifElse example in Rambda REPL

ifElse<T, TFiltered extends T, TOnTrueResult, TOnFalseResult>(
  pred: (a: T) => a is TFiltered,
  onTrue: (a: TFiltered) => TOnTrueResult,
  onFalse: (a: Exclude<T, TFiltered>) => TOnFalseResult,
): (a: T) => TOnTrueResult | TOnFalseResult;
ifElse<TArgs extends any[], TOnTrueResult, TOnFalseResult>(fn: (...args: TArgs) => boolean, onTrue: (...args: TArgs) => TOnTrueResult, onFalse: (...args: TArgs) => TOnFalseResult): (...args: TArgs) => TOnTrueResult | TOnFalseResult;

import { curry } from './curry.js'

function ifElseFn(
  condition, onTrue, onFalse
){
  return (...input) => {
    const conditionResult =
      typeof condition === 'boolean' ? condition : condition(...input)

    if (conditionResult === true){
      return onTrue(...input)
    }

    return onFalse(...input)
  }
}

export const ifElse = curry(ifElseFn)

import { always } from './always.js'
import { has } from './has.js'
import { identity } from './identity.js'
import { ifElse } from './ifElse.js'
import { prop } from './prop.js'

const condition = has('foo')
const v = function (a){
  return typeof a === 'number'
}
const t = function (a){
  return a + 1
}
const ifFn = x => prop('foo', x).length
const elseFn = () => false

test('happy', () => {
  const fn = ifElse(condition, ifFn)(elseFn)

  expect(fn({ foo : 'bar' })).toBe(3)
  expect(fn({ fo : 'bar' })).toBeFalse()
})

test('ramda spec', () => {
  const ifIsNumber = ifElse(v)
  expect(ifIsNumber(t, identity)(15)).toBe(16)
  expect(ifIsNumber(t, identity)('hello')).toBe('hello')
})

test('pass all arguments', () => {
  const identity = function (a){
    return a
  }
  const v = function (){
    return true
  }
  const onTrue = function (a, b){
    expect(a).toBe(123)
    expect(b).toBe('abc')
  }
  ifElse(
    v, onTrue, identity
  )(123, 'abc')
})

test('accept constant as condition', () => {
  const fn = ifElse(true)(always(true))(always(false))

  expect(fn()).toBeTrue()
})

test('accept constant as condition - case 2', () => {
  const fn = ifElse(
    false, always(true), always(false)
  )

  expect(fn()).toBeFalse()
})

test('curry 1', () => {
  const fn = ifElse(condition, ifFn)(elseFn)

  expect(fn({ foo : 'bar' })).toBe(3)
  expect(fn({ fo : 'bar' })).toBeFalse()
})

test('curry 2', () => {
  const fn = ifElse(condition)(ifFn)(elseFn)

  expect(fn({ foo : 'bar' })).toBe(3)
  expect(fn({ fo : 'bar' })).toBeFalse()
})

test('simple arity of 1', () => {
  const condition = x => x > 5
  const onTrue = x => x + 1
  const onFalse = x => x + 10
  const result = ifElse(
    condition, onTrue, onFalse
  )(1)
  expect(result).toBe(11)
})

test('simple arity of 2', () => {
  const condition = (x, y) => x + y > 5
  const onTrue = (x, y) => x + y + 1
  const onFalse = (x, y) => x + y + 10
  const result = ifElse(
    condition, onTrue, onFalse
  )(1, 10)
  expect(result).toBe(12)
})

import {ifElse} from 'rambda'

describe('R.ifElse', () => {
  it('happy', () => {
    const condition = (x: number) => x > 5
    const onTrue = (x: number) => `foo${x}`
    const onFalse = (x: number) => `bar${x}`
    const fn = ifElse(condition, onTrue, onFalse)
    fn // $ExpectType (x: number) => string
    const result = fn(3)
    result // $ExpectType string
  })
  it('arity of 2', () => {
    const condition = (x: number, y: string) => x + y.length > 5
    const onTrue = (x: number, y: string) => `foo${x}-${y}`
    const onFalse = (x: number, y: string) => `bar${x}-${y}`
    const fn = ifElse(condition, onTrue, onFalse)
    fn // $ExpectType (x: number, y: string) => string
    const result = fn(3, 'hello')
    result // $ExpectType string
  })
  test('DefinitelyTyped#59291', () => {
    const getLengthIfStringElseDouble = ifElse(
      (a: string | number): a is string => true,
      a => a.length,
      a => a * 2
    )

    getLengthIfStringElseDouble('foo') // $ExpectType number
    getLengthIfStringElseDouble(3) // $ExpectType number
    const result = ifElse(
      (a: {
        foo?: string,
        bar: number | string,
      }): a is {foo: string, bar: string} => true,
      (a): [string, string] => [a.foo, a.bar],
      (a): [string | undefined, string | number] => [a.foo, a.bar]
    )
    result // $ExpectType (a: { foo?: string | undefined; bar: string | number; }) => [string, string] | [string | undefined, string | number]
  })
})

inc

It increments a number.

Try this R.inc example in Rambda REPL

includes


includes<T extends string>(valueToFind: T, input: string): boolean

If input is string, then this method work as native String.includes.

If input is array, then R.equals is used to define if valueToFind belongs to the list.

Try this R.includes example in Rambda REPL

includes<T extends string>(valueToFind: T, input: string): boolean;
includes<T extends string>(valueToFind: T): (input: string) => boolean;
includes<T>(valueToFind: T, input: T[]): boolean;
includes<T>(valueToFind: T): (input: T[]) => boolean;

import { isArray } from './_internals/isArray.js'
import { _indexOf } from './equals.js'

export function includes(valueToFind, iterable){
  if (arguments.length === 1)
    return _iterable => includes(valueToFind, _iterable)
  if (typeof iterable === 'string'){
    return iterable.includes(valueToFind)
  }
  if (!iterable){
    throw new TypeError(`Cannot read property \'indexOf\' of ${ iterable }`)
  }
  if (!isArray(iterable)) return false

  return _indexOf(valueToFind, iterable) > -1
}

import { includes as includesRamda } from 'ramda'

import { includes } from './includes.js'

test('with string as iterable', () => {
  const str = 'foo bar'

  expect(includes('bar')(str)).toBeTrue()
  expect(includesRamda('bar')(str)).toBeTrue()
  expect(includes('never', str)).toBeFalse()
  expect(includesRamda('never', str)).toBeFalse()
})

test('with array as iterable', () => {
  const arr = [ 1, 2, 3 ]

  expect(includes(2)(arr)).toBeTrue()
  expect(includesRamda(2)(arr)).toBeTrue()

  expect(includes(4, arr)).toBeFalse()
  expect(includesRamda(4, arr)).toBeFalse()
})

test('with list of objects as iterable', () => {
  const arr = [ { a : 1 }, { b : 2 }, { c : 3 } ]

  expect(includes({ c : 3 }, arr)).toBeTrue()
  expect(includesRamda({ c : 3 }, arr)).toBeTrue()
})

test('with NaN', () => {
  const result = includes(NaN, [ NaN ])
  const ramdaResult = includesRamda(NaN, [ NaN ])
  expect(result).toBeTrue()
  expect(ramdaResult).toBeTrue()
})

test('with wrong input that does not throw', () => {
  const result = includes(1, /foo/g)
  const ramdaResult = includesRamda(1, /foo/g)
  expect(result).toBeFalse()
  expect(ramdaResult).toBeFalse()
})

test('throws on wrong input - match ramda behaviour', () => {
  expect(() => includes(2, null)).toThrowWithMessage(TypeError,
    'Cannot read property \'indexOf\' of null')
  expect(() => includesRamda(2, null)).toThrowWithMessage(TypeError,
    'Cannot read properties of null (reading \'indexOf\')')
  expect(() => includes(2, undefined)).toThrowWithMessage(TypeError,
    'Cannot read property \'indexOf\' of undefined')
  expect(() => includesRamda(2, undefined)).toThrowWithMessage(TypeError,
    'Cannot read properties of undefined (reading \'indexOf\')')
})

import {includes} from 'rambda'

const list = [{a: {b: '1'}}, {a: {c: '2'}}, {a: {b: '3'}}]

describe('R.includes', () => {
  it('happy', () => {
    const result = includes({a: {b: '1'}}, list)
    result // $ExpectType boolean
    const result2 = includes('oo', ['f', 'oo'])
    result2 // $ExpectType boolean
  })
  it('with string', () => {
    const str = 'foo' as 'foo' | 'bar'
    const result = includes('oo', str)
    const curriedResult = includes('oo')(str)

    result // $ExpectType boolean
    curriedResult // $ExpectType boolean
  })
})

indexBy

It generates object with properties provided by condition and values provided by list array.

If condition is a function, then all list members are passed through it.

If condition is a string, then all list members are passed through R.path(condition).

Try this R.indexBy example in Rambda REPL

indexOf

It returns the index of the first element of list equals to valueToFind.

If there is no such element, it returns -1.

Try this R.indexOf example in Rambda REPL

init


init<T extends unknown[]>(input: T): T extends readonly [...infer U, any] ? U : [...T]

It returns all but the last element of list or string input.

Try this R.init example in Rambda REPL

init<T extends unknown[]>(input: T): T extends readonly [...infer U, any] ? U : [...T];
init(input: string): string;

import baseSlice from './_internals/baseSlice.js'

export function init(listOrString){
  if (typeof listOrString === 'string') return listOrString.slice(0, -1)

  return listOrString.length ?
    baseSlice(
      listOrString, 0, -1
    ) :
    []
}

import { init } from './init.js'

test('with array', () => {
  expect(init([ 1, 2, 3 ])).toEqual([ 1, 2 ])
  expect(init([ 1, 2 ])).toEqual([ 1 ])
  expect(init([ 1 ])).toEqual([])
  expect(init([])).toEqual([])
  expect(init([])).toEqual([])
  expect(init([ 1 ])).toEqual([])
})

test('with string', () => {
  expect(init('foo')).toBe('fo')
  expect(init('f')).toBe('')
  expect(init('')).toBe('')
})

import {init} from 'rambda'

describe('R.init', () => {
  it('with string', () => {
    const result = init('foo')

    result // $ExpectType string
  })
  it('with list - one type', () => {
    const result = init([1, 2, 3])

    result // $ExpectType number[]
  })
  it('with list - mixed types', () => {
    const result = init([1, 2, 3, 'foo', 'bar'])

    result // $ExpectType (string | number)[]
  })
})

innerJoin

It returns a new list by applying a predicate function to all elements of list1 and list2 and keeping only these elements where predicate returns true.

Try this R.innerJoin example in Rambda REPL

insert

Try this R.insert example in Rambda REPL

insertAll

Try this R.insertAll example in Rambda REPL

intersection

It loops through listA and listB and returns the intersection of the two according to R.equals.

Try this R.intersection example in Rambda REPL

intersperse

It adds a separator between members of list.

Try this R.intersperse example in Rambda REPL

is

It returns true if x is instance of targetPrototype.

Try this R.is example in Rambda REPL

isEmpty


isEmpty<T>(x: T): boolean

It returns true if x is empty.

Try this R.isEmpty example in Rambda REPL

isEmpty<T>(x: T): boolean;

import { type } from './type.js'

export function isEmpty(input){
  const inputType = type(input)
  if ([ 'Undefined', 'NaN', 'Number', 'Null' ].includes(inputType))
    return false
  if (!input) return true

  if (inputType === 'Object'){
    return Object.keys(input).length === 0
  }

  if (inputType === 'Array'){
    return input.length === 0
  }

  return false
}

import { isEmpty } from './isEmpty.js'

test('happy', () => {
  expect(isEmpty(undefined)).toBeFalse()
  expect(isEmpty('')).toBeTrue()
  expect(isEmpty(null)).toBeFalse()
  expect(isEmpty(' ')).toBeFalse()
  expect(isEmpty(new RegExp(''))).toBeFalse()
  expect(isEmpty([])).toBeTrue()
  expect(isEmpty([ [] ])).toBeFalse()
  expect(isEmpty({})).toBeTrue()
  expect(isEmpty({ x : 0 })).toBeFalse()
  expect(isEmpty(0)).toBeFalse()
  expect(isEmpty(NaN)).toBeFalse()
  expect(isEmpty([ '' ])).toBeFalse()
})

import {isEmpty} from 'rambda'

describe('R.isEmpty', () => {
  it('happy', () => {
    const result = isEmpty('foo')
    result // $ExpectType boolean
  })
})

isNil


isNil(x: any): x is null | undefined

It returns true if x is either null or undefined.

Try this R.isNil example in Rambda REPL

isNil(x: any): x is null | undefined;

export function isNil(x){
  return x === undefined || x === null
}

import { isNil } from './isNil.js'

test('happy', () => {
  expect(isNil(null)).toBeTrue()

  expect(isNil(undefined)).toBeTrue()

  expect(isNil([])).toBeFalse()
})

isNotEmpty


isNotEmpty<T>(value: T[]): value is NonEmptyArray<T>

isNotEmpty<T>(value: T[]): value is NonEmptyArray<T>;
isNotEmpty<T>(value: readonly T[]): value is ReadonlyNonEmptyArray<T>;
isNotEmpty(value: any): boolean;

isNotNil

Try this R.isNotNil example in Rambda REPL

join


join<T>(glue: string, list: T[]): string

It returns a string of all list instances joined with a glue.

Try this R.join example in Rambda REPL

join<T>(glue: string, list: T[]): string;
join<T>(glue: string): (list: T[]) => string;

export function join(glue, list){
  if (arguments.length === 1) return _list => join(glue, _list)

  return list.join(glue)
}

import { join } from './join.js'

test('curry', () => {
  expect(join('|')([ 'foo', 'bar', 'baz' ])).toBe('foo|bar|baz')

  expect(join('|', [ 1, 2, 3 ])).toBe('1|2|3')

  const spacer = join(' ')

  expect(spacer([ 'a', 2, 3.4 ])).toBe('a 2 3.4')
})

import {join} from 'rambda'

describe('R.join', () => {
  it('happy', () => {
    const result = join('|', [1, 2, 3])
    result // $ExpectType string
  })
})

juxt


juxt<A extends any[], R1>(fns: [(...a: A) => R1]): (...a: A) => [R1]

It applies list of function to a list of inputs.

Try this R.juxt example in Rambda REPL

juxt<A extends any[], R1>(fns: [(...a: A) => R1]): (...a: A) => [R1];
juxt<A extends any[], R1, R2>(fns: [(...a: A) => R1, (...a: A) => R2]): (...a: A) => [R1, R2];
juxt<A extends any[], R1, R2, R3>(fns: [(...a: A) => R1, (...a: A) => R2, (...a: A) => R3]): (...a: A) => [R1, R2, R3];
juxt<A extends any[], R1, R2, R3, R4>(fns: [(...a: A) => R1, (...a: A) => R2, (...a: A) => R3, (...a: A) => R4]): (...a: A) => [R1, R2, R3, R4];
juxt<A extends any[], R1, R2, R3, R4, R5>(fns: [(...a: A) => R1, (...a: A) => R2, (...a: A) => R3, (...a: A) => R4, (...a: A) => R5]): (...a: A) => [R1, R2, R3, R4, R5];
juxt<A extends any[], U>(fns: Array<(...args: A) => U>): (...args: A) => U[];

export function juxt(listOfFunctions){
  return (...args) => listOfFunctions.map(fn => fn(...args))
}

import { juxt } from './juxt.js'

test('happy', () => {
  const fn = juxt([ Math.min, Math.max, Math.min ])
  const result = fn(
    3, 4, 9, -3
  )
  expect(result).toEqual([ -3, 9, -3 ])
})

import {juxt} from 'rambda'

describe('R.juxt', () => {
  it('happy', () => {
    const fn = juxt([Math.min, Math.max])
    const result = fn(3, 4, 9, -3)
    result // $ExpectType [number, number]
  })
})

keys


keys<T extends object>(x: T): (keyof T & string)[]

It applies Object.keys over x and returns its keys.

Try this R.keys example in Rambda REPL

keys<T extends object>(x: T): (keyof T & string)[];
keys<T>(x: T): string[];

export function keys(x){
  return Object.keys(x)
}

import { keys } from './keys.js'

test('happy', () => {
  expect(keys({ a : 1 })).toEqual([ 'a' ])
})

last


last(str: ''): undefined

It returns the last element of input, as the input can be either a string or an array. It returns undefined if array has length of 0.

Try this R.last example in Rambda REPL

last(str: ''): undefined;
last(str: string): string;
last(list: readonly[]): undefined;
last(list: never[]): undefined;
last<T extends unknown[]>(array: T): LastArrayElement<T>;
last<T extends readonly unknown[]>(array: T): LastArrayElement<T>;
last(str: string): string | undefined;

export function last(listOrString){
  if (typeof listOrString === 'string'){
    return listOrString[ listOrString.length - 1 ] || ''
  }

  return listOrString[ listOrString.length - 1 ]
}

import { last } from './last.js'

test('with list', () => {
  expect(last([ 1, 2, 3 ])).toBe(3)
  expect(last([])).toBeUndefined()
})

test('with string', () => {
  expect(last('abc')).toBe('c')
  expect(last('')).toBe('')
})

lastIndexOf


lastIndexOf<T>(target: T, list: T[]): number

It returns the last index of target in list array.

R.equals is used to determine equality between target and members of list.

If there is no such index, then -1 is returned.

Try this R.lastIndexOf example in Rambda REPL

lastIndexOf<T>(target: T, list: T[]): number;
lastIndexOf<T>(target: T): (list: T[]) => number;

import { _lastIndexOf } from './equals.js'

export function lastIndexOf(valueToFind, list){
  if (arguments.length === 1){
    return _list => _lastIndexOf(valueToFind, _list)
  }

  return _lastIndexOf(valueToFind, list)
}

import { lastIndexOf as lastIndexOfRamda } from 'ramda'

import { compareCombinations } from './_internals/testUtils.js'
import { possibleIterables, possibleTargets } from './indexOf.spec.js'
import { lastIndexOf } from './lastIndexOf.js'

test('with NaN', () => {
  expect(lastIndexOf(NaN, [ NaN ])).toBe(0)
})

test('will throw with bad input', () => {
  expect(lastIndexOfRamda([], true)).toBe(-1)
  expect(() => indexOf([], true)).toThrowErrorMatchingInlineSnapshot('"indexOf is not defined"')
})

test('without list of objects - no R.equals', () => {
  expect(lastIndexOf(3, [ 1, 2, 3, 4 ])).toBe(2)
  expect(lastIndexOf(10)([ 1, 2, 3, 4 ])).toBe(-1)
})

test('list of objects uses R.equals', () => {
  const listOfObjects = [ { a : 1 }, { b : 2 }, { c : 3 } ]
  expect(lastIndexOf({ c : 4 }, listOfObjects)).toBe(-1)
  expect(lastIndexOf({ c : 3 }, listOfObjects)).toBe(2)
})

test('list of arrays uses R.equals', () => {
  const listOfLists = [ [ 1 ], [ 2, 3 ], [ 2, 3, 4 ], [ 2, 3 ], [ 1 ], [] ]
  expect(lastIndexOf([], listOfLists)).toBe(5)
  expect(lastIndexOf([ 1 ], listOfLists)).toBe(4)
  expect(lastIndexOf([ 2, 3, 4 ], listOfLists)).toBe(2)
  expect(lastIndexOf([ 2, 3, 5 ], listOfLists)).toBe(-1)
})

test('with string as iterable', () => {
  expect(() => lastIndexOf('a', 'abc')).toThrowErrorMatchingInlineSnapshot('"Cannot read property \'indexOf\' of abc"')
  expect(lastIndexOfRamda('a', 'abc')).toBe(0)
})

describe('brute force', () => {
  compareCombinations({
    fn          : lastIndexOf,
    fnRamda     : lastIndexOfRamda,
    firstInput  : possibleTargets,
    secondInput : possibleIterables,
    callback    : errorsCounters => {
      expect(errorsCounters).toMatchInlineSnapshot(`
        {
          "ERRORS_MESSAGE_MISMATCH": 0,
          "ERRORS_TYPE_MISMATCH": 34,
          "RESULTS_MISMATCH": 0,
          "SHOULD_NOT_THROW": 51,
          "SHOULD_THROW": 0,
          "TOTAL_TESTS": 170,
        }
      `)
    },
  })
})

import {lastIndexOf} from 'rambda'

const list = [1, 2, 3]

describe('R.lastIndexOf', () => {
  it('happy', () => {
    const result = lastIndexOf(2, list)
    result // $ExpectType number
  })
  it('curried', () => {
    const result = lastIndexOf(2)(list)
    result // $ExpectType number
  })
})

length


length<T>(input: T[]): number

It returns the length property of list or string input.

Try this R.length example in Rambda REPL

length<T>(input: T[]): number;

import { isArray } from './_internals/isArray.js'

export function length(x){
  if (isArray(x)) return x.length
  if (typeof x === 'string') return x.length

  return NaN
}

import { length as lengthRamda } from 'ramda'

import { length } from './length.js'

test('happy', () => {
  expect(length('foo')).toBe(3)
  expect(length([ 1, 2, 3 ])).toBe(3)
  expect(length([])).toBe(0)
})

test('with empty string', () => {
  expect(length('')).toBe(0)
})

test('with bad input returns NaN', () => {
  expect(length(0)).toBeNaN()
  expect(length({})).toBeNaN()
  expect(length(null)).toBeNaN()
  expect(length(undefined)).toBeNaN()
})

test('with length as property', () => {
  const input1 = { length : '123' }
  const input2 = { length : null }
  const input3 = { length : '' }

  expect(length(input1)).toBeNaN()
  expect(lengthRamda(input1)).toBeNaN()
  expect(length(input2)).toBeNaN()
  expect(lengthRamda(input2)).toBeNaN()
  expect(length(input3)).toBeNaN()
  expect(lengthRamda(input3)).toBeNaN()
})

lens


lens<S, A>(getter: (s: S) => A, setter: (a: A, s: S) => S): Lens<S, A>

It returns a lens for the given getter and setter functions.

The getter gets the value of the focus; the setter sets the value of the focus.

The setter should not mutate the data structure.

Try this R.lens example in Rambda REPL

lens<S, A>(getter: (s: S) => A, setter: (a: A, s: S) => S): Lens<S, A>;

export function lens(getter, setter){
  return function (functor){
    return function (target){
      return functor(getter(target)).map(focus => setter(focus, target))
    }
  }
}

import {lens, assoc, lensProp, view, lensIndex, over, lensPath} from 'rambda'

interface Input {
  foo: string,
}
const testObject: Input = {
  foo: 'Jazz',
}

describe('R.lens', () => {
  it('happy', () => {
    const fn = lens<Input, string>((x: Input) => {
      x.foo // $ExpectType string
      return x.foo
    }, assoc('name'))
    fn // $ExpectType Lens<Input, string>
  })
})

describe('R.lensProp', () => {
  it('happy', () => {
    const result = view<Input, string>(lensProp('foo'), testObject)
    result // $ExpectType string
  })
  it('issue 740', () => {
    // @ts-expect-error
    over(lensProp('x'), (n) => String(n), {x: 1})
  })
})

describe('R.lensIndex', () => {
  const testList: Input[] = [{foo: 'bar'}, {foo: 'baz'}]
  it('happy', () => {
    const result = view<Input[], Input>(lensIndex(0), testList)
    result // $ExpectType Input
    result.foo // $ExpectType string
  })
})

describe('R.lensPath', () => {
  const path = lensPath(['bar', 'a'])
  it('happy', () => {
    const result = view<Input, string>(path, testObject)
    result // $ExpectType string
  })
})

describe('R.view', () => {
  const fooLens = lens<Input, string>((x: Input) => {
    return x.foo
  }, assoc('foo'))
  it('happt', () => {
    const result = view<Input, string>(fooLens, testObject)
    result // $ExpectType string
  })
})

lensIndex


lensIndex<A>(n: number): Lens<A[], A>

It returns a lens that focuses on specified index.

Try this R.lensIndex example in Rambda REPL

lensIndex<A>(n: number): Lens<A[], A>;
lensIndex<A extends any[], N extends number>(n: N): Lens<A, A[N]>;

import { lens } from './lens.js'
import { nth } from './nth.js'
import { update } from './update.js'

export function lensIndex(index){
  return lens(nth(index), update(index))
}

import { compose } from './compose.js'
import { keys } from './keys.js'
import { lensIndex } from './lensIndex.js'
import { over } from './over.js'
import { set } from './set.js'
import { view } from './view.js'

const testList = [ { a : 1 }, { b : 2 }, { c : 3 } ]

test('focuses list element at the specified index', () => {
  expect(view(lensIndex(0), testList)).toEqual({ a : 1 })
})

test('returns undefined if the specified index does not exist', () => {
  expect(view(lensIndex(10), testList)).toBeUndefined()
})

test('sets the list value at the specified index', () => {
  expect(set(
    lensIndex(0), 0, testList
  )).toEqual([ 0, { b : 2 }, { c : 3 } ])
})

test('applies function to the value at the specified list index', () => {
  expect(over(
    lensIndex(2), keys, testList
  )).toEqual([ { a : 1 }, { b : 2 }, [ 'c' ] ])
})

test('can be composed', () => {
  const nestedList = [ 0, [ 10, 11, 12 ], 1, 2 ]
  const composedLens = compose(lensIndex(1), lensIndex(0))

  expect(view(composedLens, nestedList)).toBe(10)
})

test('set s (get s) === s', () => {
  expect(set(
    lensIndex(0), view(lensIndex(0), testList), testList
  )).toEqual(testList)
})

test('get (set s v) === v', () => {
  expect(view(lensIndex(0), set(
    lensIndex(0), 0, testList
  ))).toBe(0)
})

test('get (set(set s v1) v2) === v2', () => {
  expect(view(lensIndex(0),
    set(
      lensIndex(0), 11, set(
        lensIndex(0), 10, testList
      )
    ))).toBe(11)
})

lensPath

It returns a lens that focuses on specified path.

Try this R.lensPath example in Rambda REPL

lensProp


lensProp<S, K extends keyof S = keyof S>(prop: K): Lens<S, S[K]>

It returns a lens that focuses on specified property prop.

Try this R.lensProp example in Rambda REPL

lensProp<S, K extends keyof S = keyof S>(prop: K): Lens<S, S[K]>;

import { assoc } from './assoc.js'
import { lens } from './lens.js'
import { prop } from './prop.js'

export function lensProp(key){
  return lens(prop(key), assoc(key))
}

import { compose } from './compose.js'
import { identity } from './identity.js'
import { inc } from './inc.js'
import { lensProp } from './lensProp.js'
import { over } from './over.js'
import { set } from './set.js'
import { view } from './view.js'

const testObj = {
  a : 1,
  b : 2,
  c : 3,
}

test('focuses object the specified object property', () => {
  expect(view(lensProp('a'), testObj)).toBe(1)
})

test('returns undefined if the specified property does not exist', () => {
  expect(view(lensProp('X'), testObj)).toBeUndefined()
})

test('sets the value of the object property specified', () => {
  expect(set(
    lensProp('a'), 0, testObj
  )).toEqual({
    a : 0,
    b : 2,
    c : 3,
  })
})

test('adds the property to the object if it doesn\'t exist', () => {
  expect(set(
    lensProp('d'), 4, testObj
  )).toEqual({
    a : 1,
    b : 2,
    c : 3,
    d : 4,
  })
})

test('applies function to the value of the specified object property', () => {
  expect(over(
    lensProp('a'), inc, testObj
  )).toEqual({
    a : 2,
    b : 2,
    c : 3,
  })
})

test('applies function to undefined and adds the property if it doesn\'t exist', () => {
  expect(over(
    lensProp('X'), identity, testObj
  )).toEqual({
    a : 1,
    b : 2,
    c : 3,
    X : undefined,
  })
})

test('can be composed', () => {
  const nestedObj = {
    a : { b : 1 },
    c : 2,
  }
  const composedLens = compose(lensProp('a'), lensProp('b'))

  expect(view(composedLens, nestedObj)).toBe(1)
})

test('set s (get s) === s', () => {
  expect(set(
    lensProp('a'), view(lensProp('a'), testObj), testObj
  )).toEqual(testObj)
})

test('get (set s v) === v', () => {
  expect(view(lensProp('a'), set(
    lensProp('a'), 0, testObj
  ))).toBe(0)
})

test('get (set(set s v1) v2) === v2', () => {
  expect(view(lensProp('a'),
    set(
      lensProp('a'), 11, set(
        lensProp('a'), 10, testObj
      )
    ))).toBe(11)
})

lt

Try this R.lt example in Rambda REPL

lte

Try this R.lte example in Rambda REPL

map


map<T, U>(fn: ObjectIterator<T, U>, iterable: Dictionary<T>): Dictionary<U>

It returns the result of looping through iterable with fn.

It works with both array and object.

Try this R.map example in Rambda REPL

map<T, U>(fn: ObjectIterator<T, U>, iterable: Dictionary<T>): Dictionary<U>;
map<T, U>(fn: Iterator<T, U>, iterable: T[]): U[];
map<T, U>(fn: Iterator<T, U>): (iterable: T[]) => U[];
map<T, U, S>(fn: ObjectIterator<T, U>): (iterable: Dictionary<T>) => Dictionary<U>;
map<T>(fn: Iterator<T, T>): (iterable: T[]) => T[];
map<T>(fn: Iterator<T, T>, iterable: T[]): T[];

import { INCORRECT_ITERABLE_INPUT } from './_internals/constants.js'
import { isArray } from './_internals/isArray.js'
import { keys } from './_internals/keys.js'

export function mapArray(
  fn, list, isIndexed = false
){
  let index = 0
  const willReturn = Array(list.length)

  while (index < list.length){
    willReturn[ index ] = isIndexed ? fn(list[ index ], index) : fn(list[ index ])

    index++
  }

  return willReturn
}

export function mapObject(fn, obj){
  if (arguments.length === 1){
    return _obj => mapObject(fn, _obj)
  }
  let index = 0
  const objKeys = keys(obj)
  const len = objKeys.length
  const willReturn = {}

  while (index < len){
    const key = objKeys[ index ]
    willReturn[ key ] = fn(
      obj[ key ], key, obj
    )
    index++
  }

  return willReturn
}

export const mapObjIndexed = mapObject

export function map(fn, iterable){
  if (arguments.length === 1) return _iterable => map(fn, _iterable)
  if (!iterable){
    throw new Error(INCORRECT_ITERABLE_INPUT)
  }

  if (isArray(iterable)) return mapArray(fn, iterable)

  return mapObject(fn, iterable)
}

import { map as mapRamda } from 'ramda'

import { map } from './map.js'

const double = x => x * 2

describe('with array', () => {
  it('happy', () => {
    expect(map(double, [ 1, 2, 3 ])).toEqual([ 2, 4, 6 ])
  })

  it('curried', () => {
    expect(map(double)([ 1, 2, 3 ])).toEqual([ 2, 4, 6 ])
  })
})

describe('with object', () => {
  const obj = {
    a : 1,
    b : 2,
  }

  it('happy', () => {
    expect(map(double, obj)).toEqual({
      a : 2,
      b : 4,
    })
  })

  it('property as second and input object as third argument', () => {
    const obj = {
      a : 1,
      b : 2,
    }
    const iterator = (
      val, prop, inputObject
    ) => {
      expect(prop).toBeString()
      expect(inputObject).toEqual(obj)

      return val * 2
    }

    expect(map(iterator)(obj)).toEqual({
      a : 2,
      b : 4,
    })
  })
})

test('bad inputs difference between Ramda and Rambda', () => {
  expect(() => map(double, null)).toThrowErrorMatchingInlineSnapshot('"Incorrect iterable input"')
  expect(() => map(double)(undefined)).toThrowErrorMatchingInlineSnapshot('"Incorrect iterable input"')
  expect(() => mapRamda(double, null)).toThrowErrorMatchingInlineSnapshot('"Cannot read properties of null (reading \'fantasy-land/map\')"')
  expect(() =>
    mapRamda(double, undefined)).toThrowErrorMatchingInlineSnapshot('"Cannot read properties of undefined (reading \'fantasy-land/map\')"')
})

import {map} from 'rambda'

describe('R.map with arrays', () => {
  it('iterable returns the same type as the input', () => {
    const result = map<number>(
      (x: number) => {
        x // $ExpectType number
        return x + 2
      },
      [1, 2, 3]
    )
    result // $ExpectType number[]
  })
  it('iterable returns the same type as the input - curried', () => {
    const result = map<number>((x: number) => {
      x // $ExpectType number
      return x + 2
    })([1, 2, 3])
    result // $ExpectType number[]
  })
  it('iterable returns different type as the input', () => {
    const result = map<number, string>(
      (x: number) => {
        x // $ExpectType number
        return String(x)
      },
      [1, 2, 3]
    )
    result // $ExpectType string[]
  })
})

describe('R.map with objects', () => {
  it('iterable with all three arguments - curried', () => {
    // It requires dummy third typing argument
    // in order to identify compared to curry typings for arrays
    // ============================================
    const result = map<number, string, any>((a, b, c) => {
      a // $ExpectType number
      b // $ExpectType string
      c // $ExpectType Dictionary<number>
      return `${a}`
    })({a: 1, b: 2})
    result // $ExpectType Dictionary<string>
  })
  it('iterable with all three arguments', () => {
    const result = map<number, string>(
      (a, b, c) => {
        a // $ExpectType number
        b // $ExpectType string
        c // $ExpectType Dictionary<number>
        return `${a}`
      },
      {a: 1, b: 2}
    )
    result // $ExpectType Dictionary<string>
  })
  it('iterable with property argument', () => {
    const result = map<number, string>(
      (a, b) => {
        a // $ExpectType number
        b // $ExpectType string
        return `${a}`
      },
      {a: 1, b: 2}
    )
    result // $ExpectType Dictionary<string>
  })
  it('iterable with no property argument', () => {
    const result = map<number, string>(
      a => {
        a // $ExpectType number
        return `${a}`
      },
      {a: 1, b: 2}
    )
    result // $ExpectType Dictionary<string>
  })
})

mapObjIndexed


mapObjIndexed<T>(fn: ObjectIterator<T, T>, iterable: Dictionary<T>): Dictionary<T>

It works the same way as R.map does for objects. It is added as Ramda also has this method.

Try this R.mapObjIndexed example in Rambda REPL

mapObjIndexed<T>(fn: ObjectIterator<T, T>, iterable: Dictionary<T>): Dictionary<T>;
mapObjIndexed<T, U>(fn: ObjectIterator<T, U>, iterable: Dictionary<T>): Dictionary<U>;
mapObjIndexed<T>(fn: ObjectIterator<T, T>): (iterable: Dictionary<T>) => Dictionary<T>;
mapObjIndexed<T, U>(fn: ObjectIterator<T, U>): (iterable: Dictionary<T>) => Dictionary<U>;

import {mapObjIndexed} from 'rambda'

const obj = {a: 1, b: 2, c: 3}

describe('R.mapObjIndexed', () => {
  it('without type transform', () => {
    const result = mapObjIndexed((x, prop, obj) => {
      x // $ExpectType number
      prop // $ExpectType string
      obj // $ExpectType Dictionary<number>
      return x + 2
    }, obj)
    result // $ExpectType Dictionary<number>
  })
  it('without type transform - curried', () => {
    const result = mapObjIndexed<number>((x, prop, obj) => {
      x // $ExpectType number
      prop // $ExpectType string
      obj // $ExpectType Dictionary<number>
      return x + 2
    })(obj)
    result // $ExpectType Dictionary<number>
  })
  it('change of type', () => {
    const result = mapObjIndexed((x, prop, obj) => {
      x // $ExpectType number
      prop // $ExpectType string
      obj // $ExpectType Dictionary<number>
      return String(x + 2)
    }, obj)
    result // $ExpectType Dictionary<string>
  })
  it('change of type - curried', () => {
    const result = mapObjIndexed<number, string>((x, prop, obj) => {
      x // $ExpectType number
      prop // $ExpectType string
      obj // $ExpectType Dictionary<number>
      return String(x + 2)
    })(obj)
    result // $ExpectType Dictionary<string>
  })
})

match


match(regExpression: RegExp, str: string): string[]

Curried version of String.prototype.match which returns empty array, when there is no match.

Try this R.match example in Rambda REPL

match(regExpression: RegExp, str: string): string[];
match(regExpression: RegExp): (str: string) => string[];

export function match(pattern, input){
  if (arguments.length === 1) return _input => match(pattern, _input)

  const willReturn = input.match(pattern)

  return willReturn === null ? [] : willReturn
}

import { equals } from './equals.js'
import { match } from './match.js'

test('happy', () => {
  expect(match(/a./g)('foo bar baz')).toEqual([ 'ar', 'az' ])
})

test('fallback', () => {
  expect(match(/a./g)('foo')).toEqual([])
})

test('with string', () => {
  expect(match('a', 'foo')).toEqual([])
  expect(equals(match('o', 'foo'), [ 'o' ])).toBeTrue()
})

test('throwing', () => {
  expect(() => {
    match(/a./g, null)
  }).toThrowErrorMatchingInlineSnapshot('"Cannot read properties of null (reading \'match\')"')
})

import {match} from 'rambda'

const str = 'foo bar'

describe('R.match', () => {
  it('happy', () => {
    const result = match(/foo/, str)
    result // $ExpectType string[]
  })
  it('curried', () => {
    const result = match(/foo/)(str)
    result // $ExpectType string[]
  })
})

mathMod

R.mathMod behaves like the modulo operator should mathematically, unlike the % operator (and by extension, R.modulo). So while -17 % 5 is -2, mathMod(-17, 5) is 3.

Try this R.mathMod example in Rambda REPL

max

It returns the greater value between x and y.

Try this R.max example in Rambda REPL

maxBy

It returns the greater value between x and y according to compareFn function.

Try this R.maxBy example in Rambda REPL

mean


mean(list: number[]): number

It returns the mean value of list input.

Try this R.mean example in Rambda REPL

mean(list: number[]): number;

import { sum } from './sum.js'

export function mean(list){
  return sum(list) / list.length
}

import { mean } from './mean.js'

test('happy', () => {
  expect(mean([ 2, 7 ])).toBe(4.5)
})

test('with NaN', () => {
  expect(mean([])).toBeNaN()
})

import {mean} from 'rambda'

describe('R.mean', () => {
  it('happy', () => {
    const result = mean([1, 2, 3])

    result // $ExpectType number
  })
})

median


median(list: number[]): number

It returns the median value of list input.

Try this R.median example in Rambda REPL

median(list: number[]): number;

import { mean } from './mean.js'

export function median(list){
  const len = list.length
  if (len === 0) return NaN
  const width = 2 - len % 2
  const idx = (len - width) / 2

  return mean(Array.prototype.slice
    .call(list, 0)
    .sort((a, b) => {
      if (a === b) return 0

      return a < b ? -1 : 1
    })
    .slice(idx, idx + width))
}

import { median } from './median.js'

test('happy', () => {
  expect(median([ 2 ])).toBe(2)
  expect(median([ 7, 2, 10, 2, 9 ])).toBe(7)
})

test('with empty array', () => {
  expect(median([])).toBeNaN()
})

import {median} from 'rambda'

describe('R.median', () => {
  it('happy', () => {
    const result = median([1, 2, 3])

    result // $ExpectType number
  })
})

merge

Same as R.mergeRight.

mergeAll


mergeAll<T>(list: object[]): T

It merges all objects of list array sequentially and returns the result.

Try this R.mergeAll example in Rambda REPL

mergeAll<T>(list: object[]): T;
mergeAll(list: object[]): object;

import { map } from './map.js'
import { mergeRight } from './mergeRight.js'

export function mergeAll(arr){
  let willReturn = {}
  map(val => {
    willReturn = mergeRight(willReturn, val)
  }, arr)

  return willReturn
}

import { mergeAll } from './mergeAll.js'

test('case 1', () => {
  const arr = [ { a : 1 }, { b : 2 }, { c : 3 } ]
  const expectedResult = {
    a : 1,
    b : 2,
    c : 3,
  }
  expect(mergeAll(arr)).toEqual(expectedResult)
})

test('case 2', () => {
  expect(mergeAll([ { foo : 1 }, { bar : 2 }, { baz : 3 } ])).toEqual({
    foo : 1,
    bar : 2,
    baz : 3,
  })
})

describe('acts as if nil values are simply empty objects', () => {
  it('if the first object is nil', () => {
    expect(mergeAll([ null, { foo : 1 }, { foo : 2 }, { bar : 2 } ])).toEqual({
      foo : 2,
      bar : 2,
    })
  })

  it('if the last object is nil', () => {
    expect(mergeAll([ { foo : 1 }, { foo : 2 }, { bar : 2 }, undefined ])).toEqual({
      foo : 2,
      bar : 2,
    })
  })

  it('if an intermediate object is nil', () => {
    expect(mergeAll([ { foo : 1 }, { foo : 2 }, null, { bar : 2 } ])).toEqual({
      foo : 2,
      bar : 2,
    })
  })
})

import {mergeAll} from 'rambda'

describe('R.mergeAll', () => {
  it('with passing type', () => {
    interface Output {
      foo: number,
      bar: number,
    }
    const result = mergeAll<Output>([{foo: 1}, {bar: 2}])
    result.foo // $ExpectType number
    result.bar // $ExpectType number
  })

  it('without passing type', () => {
    const result = mergeAll([{foo: 1}, {bar: 2}])
    result // $ExpectType unknown
  })
})

mergeDeepLeft

Try this R.mergeDeepLeft example in Rambda REPL

mergeDeepRight


mergeDeepRight<Output>(target: object, newProps: object): Output

Creates a new object with the own properties of the first object merged with the own properties of the second object. If a key exists in both objects:

and both values are objects, the two values will be recursively merged
otherwise the value from the second object will be used.

mergeDeepRight<Output>(target: object, newProps: object): Output;
mergeDeepRight<Output>(target: object): (newProps: object) => Output;

import { clone } from './clone.js'
import { type } from './type.js'

export function mergeDeepRight(target, source){
  if (arguments.length === 1){
    return sourceHolder => mergeDeepRight(target, sourceHolder)
  }

  const willReturn = clone(target)

  Object.keys(source).forEach(key => {
    if (type(source[ key ]) === 'Object'){
      if (type(target[ key ]) === 'Object'){
        willReturn[ key ] = mergeDeepRight(target[ key ], source[ key ])
      } else {
        willReturn[ key ] = source[ key ]
      }
    } else {
      willReturn[ key ] = source[ key ]
    }
  })

  return willReturn
}

import { mergeDeepRight } from './mergeDeepRight.js'

const student = {
  name    : 'foo',
  age     : 10,
  contact : {
    a     : 1,
    email : '[email protected]',
  },
}
const teacher = {
  age     : 40,
  contact : { email : '[email protected]' },
  songs   : { title : 'Remains the same' },
}

test('when merging object with lists inside them', () => {
  const a = {
    a : [ 1, 2, 3 ],
    b : [ 4, 5, 6 ],
  }
  const b = {
    a : [ 7, 8, 9 ],
    b : [ 10, 11, 12 ],
  }
  const result = mergeDeepRight(a, b)
  const expected = {
    a : [ 7, 8, 9 ],
    b : [ 10, 11, 12 ],
  }
  expect(result).toEqual(expected)
})

test('happy', () => {
  const result = mergeDeepRight(student, teacher)
  const curryResult = mergeDeepRight(student)(teacher)
  const expected = {
    age     : 40,
    name    : 'foo',
    contact : {
      a     : 1,
      email : '[email protected]',
    },
    songs : { title : 'Remains the same' },
  }

  expect(result).toEqual(expected)
  expect(curryResult).toEqual(expected)
})

test('issue 650', () => {
  expect(Object.keys(mergeDeepRight({ a : () => {} }, { b : () => {} }))).toEqual([
    'a',
    'b',
  ])
})

test('ramda compatible test 1', () => {
  const a = {
    w : 1,
    x : 2,
    y : { z : 3 },
  }
  const b = {
    a : 4,
    b : 5,
    c : { d : 6 },
  }
  const result = mergeDeepRight(a, b)
  const expected = {
    w : 1,
    x : 2,
    y : { z : 3 },
    a : 4,
    b : 5,
    c : { d : 6 },
  }

  expect(result).toEqual(expected)
})

test('ramda compatible test 2', () => {
  const a = {
    a : {
      b : 1,
      c : 2,
    },
    y : 0,
  }
  const b = {
    a : {
      b : 3,
      d : 4,
    },
    z : 0,
  }
  const result = mergeDeepRight(a, b)
  const expected = {
    a : {
      b : 3,
      c : 2,
      d : 4,
    },
    y : 0,
    z : 0,
  }

  expect(result).toEqual(expected)
})

test('ramda compatible test 3', () => {
  const a = {
    w : 1,
    x : { y : 2 },
  }
  const result = mergeDeepRight(a, { x : { y : 3 } })
  const expected = {
    w : 1,
    x : { y : 3 },
  }
  expect(result).toEqual(expected)
})

test('functions are not discarded', () => {
  const obj = { foo : () => {} }
  expect(typeof mergeDeepRight(obj, {}).foo).toBe('function')
})

import {mergeDeepRight} from 'rambda'

interface Output {
  foo: {
    bar: number,
  },
}

describe('R.mergeDeepRight', () => {
  const result = mergeDeepRight<Output>({foo: {bar: 1}}, {foo: {bar: 2}})
  result.foo.bar // $ExpectType number
})

mergeLeft


mergeLeft<Output>(newProps: object, target: object): Output

Same as R.merge, but in opposite direction.

Try this R.mergeLeft example in Rambda REPL

mergeLeft<Output>(newProps: object, target: object): Output;
mergeLeft<Output>(newProps: object): (target: object) => Output;

import { mergeRight } from './mergeRight.js'

export function mergeLeft(x, y){
  if (arguments.length === 1) return _y => mergeLeft(x, _y)

  return mergeRight(y, x)
}

import { mergeLeft } from './mergeLeft.js'

const obj = {
  foo : 1,
  bar : 2,
}

test('happy', () => {
  expect(mergeLeft({ bar : 20 }, obj)).toEqual({
    foo : 1,
    bar : 20,
  })
})

test('curry', () => {
  expect(mergeLeft({ baz : 3 })(obj)).toEqual({
    foo : 1,
    bar : 2,
    baz : 3,
  })
})

test('when undefined or null instead of object', () => {
  expect(mergeLeft(null, undefined)).toEqual({})
  expect(mergeLeft(obj, null)).toEqual(obj)
  expect(mergeLeft(obj, undefined)).toEqual(obj)
  expect(mergeLeft(undefined, obj)).toEqual(obj)
})

import {mergeLeft} from 'rambda'

interface Output {
  foo: number,
  bar: number,
}

describe('R.mergeLeft', () => {
  const result = mergeLeft<Output>({foo: 1}, {bar: 2})
  const curriedResult = mergeLeft<Output>({foo: 1})({bar: 2})

  result.foo // $ExpectType number
  result.bar // $ExpectType number
  curriedResult.bar // $ExpectType number
})

mergeRight

It creates a copy of target object with overwritten newProps properties. Previously known as R.merge but renamed after Ramda did the same.

Try this R.mergeRight example in Rambda REPL

mergeWith


mergeWith(fn: (x: any, z: any) => any, a: Record<string, unknown>, b: Record<string, unknown>): Record<string, unknown>

It takes two objects and a function, which will be used when there is an overlap between the keys.

Try this R.mergeWith example in Rambda REPL

mergeWith(fn: (x: any, z: any) => any, a: Record<string, unknown>, b: Record<string, unknown>): Record<string, unknown>;
mergeWith<Output>(fn: (x: any, z: any) => any, a: Record<string, unknown>, b: Record<string, unknown>): Output;
mergeWith(fn: (x: any, z: any) => any, a: Record<string, unknown>): (b: Record<string, unknown>) => Record<string, unknown>;
mergeWith<Output>(fn: (x: any, z: any) => any, a: Record<string, unknown>): (b: Record<string, unknown>) => Output;
mergeWith(fn: (x: any, z: any) => any): <U, V>(a: U, b: V) => Record<string, unknown>;
mergeWith<Output>(fn: (x: any, z: any) => any): <U, V>(a: U, b: V) => Output;

import { curry } from './curry.js'

export function mergeWithFn(
  mergeFn, aInput, bInput
){
  const a = aInput ?? {}
  const b = bInput ?? {}
  const willReturn = {}

  Object.keys(a).forEach(key => {
    if (b[ key ] === undefined) willReturn[ key ] = a[ key ]
    else willReturn[ key ] = mergeFn(a[ key ], b[ key ])
  })

  Object.keys(b).forEach(key => {
    if (willReturn[ key ] !== undefined) return

    if (a[ key ] === undefined) willReturn[ key ] = b[ key ]
    else willReturn[ key ] = mergeFn(a[ key ], b[ key ])
  })

  return willReturn
}

export const mergeWith = curry(mergeWithFn)

import { concat } from './concat.js'
import { mergeWithFn } from './mergeWith.js'

test('happy', () => {
  const result = mergeWithFn(
    concat,
    {
      a      : true,
      values : [ 10, 20 ],
    },
    {
      b      : true,
      values : [ 15, 35 ],
    }
  )
  const expected = {
    a      : true,
    b      : true,
    values : [ 10, 20, 15, 35 ],
  }
  expect(result).toEqual(expected)
})

// https://github.com/ramda/ramda/pull/3222/files#diff-d925d9188b478d2f1d4b26012c6dddac374f9e9d7a336604d654b9a113bfc857
describe('acts as if nil values are simply empty objects', () => {
  it('if the first object is nil and the second empty', () => {
    expect(mergeWithFn(
      concat, undefined, {}
    )).toEqual({})
  })

  it('if the first object is empty and the second nil', () => {
    expect(mergeWithFn(
      concat, {}, null
    )).toEqual({})
  })

  it('if both objects are nil', () => {
    expect(mergeWithFn(
      concat, undefined, null
    )).toEqual({})
  })

  it('if the first object is not empty and the second is nil', () => {
    expect(mergeWithFn(
      concat, { a : 'a' }, null
    )).toEqual({ a : 'a' })
  })

  it('if the first object is nil and the second is not empty', () => {
    expect(mergeWithFn(
      concat, undefined, { a : 'a' }
    )).toEqual({ a : 'a' })
  })
})

import {concat, mergeWith} from 'rambda'

interface Output {
  a: boolean,
  b: boolean,
  values: number[],
}
const A = {
  a: true,
  values: [10, 20],
}
const B = {
  b: true,
  values: [15, 35],
}

describe('R.mergeWith', () => {
  test('no curry | without explicit types', () => {
    const result = mergeWith(concat, A, B)
    result // $ExpectType Record<string, unknown>
  })
  test('no curry | with explicit types', () => {
    const result = mergeWith<Output>(concat, A, B)
    result // $ExpectType Output
  })
  test('curry 1 | without explicit types', () => {
    const result = mergeWith(concat, A)(B)
    result // $ExpectType Record<string, unknown>
  })
  test('curry 1 | with explicit types', () => {
    const result = mergeWith<Output>(concat, A)(B)
    result // $ExpectType Output
  })
  test('curry 2 | without explicit types', () => {
    const result = mergeWith(concat)(A, B)
    result // $ExpectType Record<string, unknown>
  })
  test('curry 2 | with explicit types', () => {
    const result = mergeWith<Output>(concat)(A, B)
    result // $ExpectType Output
  })
})

min

It returns the lesser value between x and y.

Try this R.min example in Rambda REPL

minBy

It returns the lesser value between x and y according to compareFn function.

Try this R.minBy example in Rambda REPL

modify


modify<K extends PropertyKey, T>(prop: K, fn: (value: T) => T): <U extends Record<K, T>>(object: U) => U

Try this R.modify example in Rambda REPL

modify<K extends PropertyKey, T>(prop: K, fn: (value: T) => T): <U extends Record<K, T>>(object: U) => U;
modify<U, K extends keyof U>(prop: K, fn: (value: U[K]) => U[K], object: U): U;
modify<K extends PropertyKey>(prop: K): {
  <T>(fn: (value: T) => T): <U extends Record<K, T>>(object: U) => U;
  <T, U extends Record<K, T>>(fn: (value: T) => T, object: U): U;
};

import { isArray } from './_internals/isArray.js'
import { isIterable } from './_internals/isIterable.js'
import { curry } from './curry.js'
import { updateFn } from './update.js'

function modifyFn(
  property, fn, iterable
){
  if (!isIterable(iterable)) return iterable
  if (iterable[ property ] === undefined) return iterable
  if (isArray(iterable)){
    return updateFn(
      property, fn(iterable[ property ]), iterable
    )
  }

  return {
    ...iterable,
    [ property ] : fn(iterable[ property ]),
  }
}

export const modify = curry(modifyFn)

import { modify as modifyRamda } from 'ramda'

import { compareCombinations, FALSY_VALUES } from './_internals/testUtils.js'
import { add } from './add.js'
import { compose } from './compose.js'
import { modify } from './modify.js'

const person = {
  name : 'foo',
  age  : 20,
}

test('happy', () => {
  expect(modify(
    'age', x => x + 1, person
  )).toEqual({
    name : 'foo',
    age  : 21,
  })
})

test('property is missing', () => {
  expect(modify(
    'foo', x => x + 1, person
  )).toEqual(person)
})

test('adjust if `array` at the given key with the `transformation` function', () => {
  expect(modify(
    1, add(1), [ 100, 1400 ]
  )).toEqual([ 100, 1401 ])
})

describe('ignores transformations if the input value is not Array and Object', () => {
  ;[ 42, undefined, null, '' ].forEach(value => {
    it(`${ value }`, () => {
      expect(modify(
        'a', add(1), value
      )).toEqual(value)
    })
  })
})

const possibleProperties = [ ...FALSY_VALUES, 'foo', 0 ]
const possibleTransformers = [
  ...FALSY_VALUES,
  add(1),
  add('foo'),
  compose,
  String,
]
const possibleObjects = [
  ...FALSY_VALUES,
  {},
  [ 1, 2, 3 ],
  {
    a   : 1,
    foo : 2,
  },
  {
    a   : 1,
    foo : [ 1 ],
  },
  {
    a   : 1,
    foo : 'bar',
  },
]

describe('brute force', () => {
  compareCombinations({
    fn          : modify,
    fnRamda     : modifyRamda,
    firstInput  : possibleProperties,
    secondInput : possibleTransformers,
    thirdInput  : possibleObjects,
    callback    : errorsCounters => {
      expect(errorsCounters).toMatchInlineSnapshot(`
        {
          "ERRORS_MESSAGE_MISMATCH": 0,
          "ERRORS_TYPE_MISMATCH": 0,
          "RESULTS_MISMATCH": 0,
          "SHOULD_NOT_THROW": 0,
          "SHOULD_THROW": 0,
          "TOTAL_TESTS": 630,
        }
      `)
    },
  })
})

import { add, identity, map, modify, pipe, toUpper } from 'rambda';

type Obj = {
	foo: string;
	bar: number;
};

describe('R.modify', () => {
	it('ramda tests', () => {
		const result1 = modify('foo', toUpper, {} as Obj);
		result1; // $ExpectType Obj

		const result2 = modify('bar', add(1), {} as Obj);
		result2; // $ExpectType Obj

		const result3 = modify('foo', toUpper)({} as Obj);
		result3; // $ExpectType Obj

		const result4 = modify('bar', add(1))({} as Obj);
		result4; // $ExpectType Obj

		const result5 = modify('foo')(toUpper)({} as Obj);
		result5; // $ExpectType Obj

		const result6 = modify('bar')(add(1))({} as Obj);
		result6; // $ExpectType Obj

		const result7 = modify('foo')(toUpper, {} as Obj);
		result7; // $ExpectType Obj

		const result8 = modify('bar')(add(1), {} as Obj);
		result8; // $ExpectType Obj

		const result9 = modify('foo', identity, {} as Obj);
		result9; // $ExpectType Obj

		// @ts-expect-error
		modify('foo', add(1), {} as Obj);
		// @ts-expect-error
		modify('bar', toUpper, {} as Obj);

		const f = pipe(map<Obj, Obj>(modify('foo', toUpper)));

		f([] as Obj[]); // $ExpectType Obj[]
	});
});

modifyPath

It changes a property of object on the base of provided path and transformer function.

Try this R.modifyPath example in Rambda REPL

modulo

Curried version of x%y.

Try this R.modulo example in Rambda REPL

move

It returns a copy of list with exchanged fromIndex and toIndex elements.

Try this R.move example in Rambda REPL

multiply

Curried version of x*y.

Try this R.multiply example in Rambda REPL

negate

Try this R.negate example in Rambda REPL

none


none<T>(predicate: (x: T) => boolean, list: T[]): boolean

It returns true, if all members of array list returns false, when applied as argument to predicate function.

Try this R.none example in Rambda REPL

none<T>(predicate: (x: T) => boolean, list: T[]): boolean;
none<T>(predicate: (x: T) => boolean): (list: T[]) => boolean;

export function none(predicate, list){
  if (arguments.length === 1) return _list => none(predicate, _list)

  for (let i = 0; i < list.length; i++){
    if (predicate(list[ i ])) return false
  }

  return true
}

import { none } from './none.js'

const isEven = n => n % 2 === 0

test('when true', () => {
  expect(none(isEven, [ 1, 3, 5, 7 ])).toBeTrue()
})

test('when false curried', () => {
  expect(none(input => input > 1, [ 1, 2, 3 ])).toBeFalse()
})

import {none} from 'rambda'

describe('R.none', () => {
  it('happy', () => {
    const result = none(
      x => {
        x // $ExpectType number
        return x > 0
      },
      [1, 2, 3]
    )
    result // $ExpectType boolean
  })
  it('curried needs a type', () => {
    const result = none<number>(x => {
      x // $ExpectType number
      return x > 0
    })([1, 2, 3])
    result // $ExpectType boolean
  })
})

not


not(input: any): boolean

It returns a boolean negated version of input.

Try this R.not example in Rambda REPL

not(input: any): boolean;

export function not(input){
  return !input
}

import { not } from './not.js'

test('not', () => {
  expect(not(false)).toBeTrue()
  expect(not(true)).toBeFalse()
  expect(not(0)).toBeTrue()
  expect(not(1)).toBeFalse()
})

import {not} from 'rambda'

describe('R.not', () => {
  it('happy', () => {
    const result = not(4)

    result // $ExpectType boolean
  })
})

nth


nth(index: number, input: string): string

Curried version of input[index].

Try this R.nth example in Rambda REPL

nth(index: number, input: string): string;	
nth<T>(index: number, input: T[]): T | undefined;	
nth(n: number): {
  <T>(input: T[]): T | undefined;
  (input: string): string;
};

export function nth(index, input){
  if (arguments.length === 1) return _input => nth(index, _input)

  const idx = index < 0 ? input.length + index : index

  return Object.prototype.toString.call(input) === '[object String]' ?
    input.charAt(idx) :
    input[ idx ]
}

import { nth } from './nth.js'

test('happy', () => {
  expect(nth(2, [ 1, 2, 3, 4 ])).toBe(3)
})

test('with curry', () => {
  expect(nth(2)([ 1, 2, 3, 4 ])).toBe(3)
})

test('with string and correct index', () => {
  expect(nth(2)('foo')).toBe('o')
})

test('with string and invalid index', () => {
  expect(nth(20)('foo')).toBe('')
})

test('with negative index', () => {
  expect(nth(-3)([ 1, 2, 3, 4 ])).toBe(2)
})

import {nth} from 'rambda'

const list = [1, 2, 3]

describe('R.nth', () => {
  it('happy', () => {
    const result = nth(4, list)

    result // $ExpectType number | undefined
  })
  it('curried', () => {
    const result = nth(1)(list)

    result // $ExpectType number | undefined
  })
})

describe('R.nth - string', () => {
  const str = 'abc'
  it('happy', () => {
    const result = nth(4, str)

    result // $ExpectType string
  })
  it('curried', () => {
    const result = nth(1)(str)

    result // $ExpectType string
  })
})

objOf

It creates an object with a single key-value pair.

Try this R.objOf example in Rambda REPL

of


of<T>(x: T): T[]

Try this R.of example in Rambda REPL

of<T>(x: T): T[];

export function of(value){
  return [ value ]
}

import { of } from './of.js'

test('happy', () => {
  expect(of(3)).toEqual([ 3 ])

  expect(of(null)).toEqual([ null ])
})

import {of} from 'rambda'

const list = [1, 2, 3]

describe('R.of', () => {
  it('happy', () => {
    const result = of(4)

    result // $ExpectType number[]
  })
  it('curried', () => {
    const result = of(list)

    result // $ExpectType number[][]
  })
})

omit


omit<T, K extends string>(propsToOmit: K[], obj: T): Omit<T, K>

It returns a partial copy of an obj without propsToOmit properties.

Try this R.omit example in Rambda REPL

omit<T, K extends string>(propsToOmit: K[], obj: T): Omit<T, K>;
omit<K extends string>(propsToOmit: K[]): <T>(obj: T) => Omit<T, K>;
omit<T, U>(propsToOmit: string, obj: T): U;
omit<T, U>(propsToOmit: string): (obj: T) => U;
omit<T>(propsToOmit: string, obj: object): T;
omit<T>(propsToOmit: string): (obj: object) => T;

import { createPath } from './_internals/createPath.js'
import { includes } from './_internals/includes.js'

export function omit(propsToOmit, obj){
  if (arguments.length === 1) return _obj => omit(propsToOmit, _obj)

  if (obj === null || obj === undefined)
    return undefined

  const propsToOmitValue = createPath(propsToOmit, ',')
  const willReturn = {}

  for (const key in obj)
    if (!includes(key, propsToOmitValue))
      willReturn[ key ] = obj[ key ]

  return willReturn
}

import { omit } from './omit.js'

test('with string as condition', () => {
  const obj = {
    a : 1,
    b : 2,
    c : 3,
  }
  const result = omit('a,c', obj)
  const resultCurry = omit('a,c')(obj)
  const expectedResult = { b : 2 }

  expect(result).toEqual(expectedResult)
  expect(resultCurry).toEqual(expectedResult)
})

test.only('with number as property to omit', () => {
  const obj = {
    1 : 1,
    b : 2,
  }
  const result = omit([ 1 ], obj)
  expect(result).toEqual({ b : 2 })
})

test('with null', () => {
  expect(omit('a,b', null)).toBeUndefined()
})

test('happy', () => {
  expect(omit([ 'a', 'c' ])({
    a : 'foo',
    b : 'bar',
    c : 'baz',
  })).toEqual({ b : 'bar' })
})

import {omit} from 'rambda'

describe('R.omit with array as props input', () => {
  it('allow Typescript to infer object type', () => {
    const input = {a: 'foo', b: 2, c: 3, d: 4}
    const result = omit(['b,c'], input)

    result.a // $ExpectType string
    result.d // $ExpectType number

    const curriedResult = omit(['a,c'], input)

    curriedResult.a // $ExpectType string
    curriedResult.d // $ExpectType number
  })

  it('declare type of input object', () => {
    interface Input {
      a: string,
      b: number,
      c: number,
      d: number,
    }
    const input: Input = {a: 'foo', b: 2, c: 3, d: 4}
    const result = omit(['b,c'], input)
    result // $ExpectType Omit<Input, "b,c">

    result.a // $ExpectType string
    result.d // $ExpectType number

    const curriedResult = omit(['a,c'], input)

    curriedResult.a // $ExpectType string
    curriedResult.d // $ExpectType number
  })
})

describe('R.omit with string as props input', () => {
  interface Output {
    b: number,
    d: number,
  }

  it('explicitly declare output', () => {
    const result = omit<Output>('a,c', {a: 1, b: 2, c: 3, d: 4})
    result // $ExpectType Output
    result.b // $ExpectType number

    const curriedResult = omit<Output>('a,c')({a: 1, b: 2, c: 3, d: 4})

    curriedResult.b // $ExpectType number
  })

  it('explicitly declare input and output', () => {
    interface Input {
      a: number,
      b: number,
      c: number,
      d: number,
    }
    const result = omit<Input, Output>('a,c', {a: 1, b: 2, c: 3, d: 4})
    result // $ExpectType Output
    result.b // $ExpectType number

    const curriedResult = omit<Input, Output>('a,c')({
      a: 1,
      b: 2,
      c: 3,
      d: 4,
    })

    curriedResult.b // $ExpectType number
  })

  it('without passing type', () => {
    const result = omit('a,c', {a: 1, b: 2, c: 3, d: 4})
    result // $ExpectType unknown
  })
})

on

It passes the two inputs through unaryFn and then the results are passed as inputs the the binaryFn to receive the final result(binaryFn(unaryFn(FIRST_INPUT), unaryFn(SECOND_INPUT))).

This method is also known as P combinator.

Try this R.on example in Rambda REPL

once


once<T extends AnyFunction, C = unknown>(fn: T, context?: C): T

It returns a function, which invokes only once fn function.

Try this R.once example in Rambda REPL

once<T extends AnyFunction, C = unknown>(fn: T, context?: C): T;

import { curry } from './curry.js'

function onceFn(fn, context){
  let result

  return function (){
    if (fn){
      result = fn.apply(context || this, arguments)
      fn = null
    }

    return result
  }
}

export function once(fn, context){
  if (arguments.length === 1){
    const wrap = onceFn(fn, context)

    return curry(wrap)
  }

  return onceFn(fn, context)
}

import { once } from './once.js'

test('with counter', () => {
  let counter = 0
  const runOnce = once(x => {
    counter++

    return x + 2
  })
  expect(runOnce(1)).toBe(3)
  runOnce(1)
  runOnce(1)
  runOnce(1)
  expect(counter).toBe(1)
})

test('happy path', () => {
  const addOneOnce = once((
    a, b, c
  ) => a + b + c, 1)

  expect(addOneOnce(
    10, 20, 30
  )).toBe(60)
  expect(addOneOnce(40)).toBe(60)
})

test('with context', () => {
  const context = { name: 'fris' }
  const getNameOnce = once(function (){
    return this.name
  }, context)

  expect(getNameOnce()).toBe('fris')
  expect(getNameOnce()).toBe('fris')
  expect(getNameOnce()).toBe('fris')
})

import {once} from 'rambda'

describe('R.once', () => {
  it('happy', () => {
    const runOnce = once((x: number) => {
      return x + 2
    })

    const result = runOnce(1)
    result // $ExpectType number
  })
  it('with context', () => {
    const runOnce = once(function (this: any, x: number) {
      return x + 2
    })

    const result = runOnce.call({}, 1)
    result // $ExpectType number
  })
})

or

Logical OR

Try this R.or example in Rambda REPL

over


over<S, A>(lens: Lens<S, A>): {
  (fn: (a: A) => A): (value: S) => S

It returns a copied Object or Array with modified value received by applying function fn to lens focus.

Try this R.over example in Rambda REPL

over<S, A>(lens: Lens<S, A>): {
  (fn: (a: A) => A): (value: S) => S;
  (fn: (a: A) => A, value: S): S;
};
over<S, A>(lens: Lens<S, A>, fn: (a: A) => A): (value: S) => S;
over<S, A>(lens: Lens<S, A>, fn: (a: A) => A, value: S): S;

import { curry } from './curry.js'

const Identity = x => ({
  x,
  map : fn => Identity(fn(x)),
})

function overFn(
  lens, fn, object
){
  return lens(x => Identity(fn(x)))(object).x
}

export const over = curry(overFn)

import { assoc } from './assoc.js'
import { lens } from './lens.js'
import { lensIndex } from './lensIndex.js'
import { lensPath } from './lensPath.js'
import { over } from './over.js'
import { prop } from './prop.js'
import { toUpper } from './toUpper.js'

const testObject = {
  foo : 'bar',
  baz : {
    a : 'x',
    b : 'y',
  },
}

test('assoc lens', () => {
  const assocLens = lens(prop('foo'), assoc('foo'))
  const result = over(
    assocLens, toUpper, testObject
  )
  const expected = {
    ...testObject,
    foo : 'BAR',
  }
  expect(result).toEqual(expected)
})

test('path lens', () => {
  const pathLens = lensPath('baz.a')
  const result = over(
    pathLens, toUpper, testObject
  )
  const expected = {
    ...testObject,
    baz : {
      a : 'X',
      b : 'y',
    },
  }
  expect(result).toEqual(expected)
})

test('index lens', () => {
  const indexLens = lensIndex(0)
  const result = over(indexLens, toUpper)([ 'foo', 'bar' ])
  expect(result).toEqual([ 'FOO', 'bar' ])
})

partial


partial<V0, V1, T>(fn: (x0: V0, x1: V1) => T, args: [V0]): (x1: V1) => T

It is very similar to R.curry, but you can pass initial arguments when you create the curried function.

R.partial will keep returning a function until all the arguments that the function fn expects are passed. The name comes from the fact that you partially inject the inputs.

Try this R.partial example in Rambda REPL

partial<V0, V1, T>(fn: (x0: V0, x1: V1) => T, args: [V0]): (x1: V1) => T;
partial<V0, V1, V2, T>(fn: (x0: V0, x1: V1, x2: V2) => T, args: [V0, V1]): (x2: V2) => T;
partial<V0, V1, V2, T>(fn: (x0: V0, x1: V1, x2: V2) => T, args: [V0]): (x1: V1, x2: V2) => T;
partial<V0, V1, V2, V3, T>(
  fn: (x0: V0, x1: V1, x2: V2, x3: V3) => T,
  args: [V0, V1, V2],
): (x2: V3) => T;
partial<V0, V1, V2, V3, T>(
  fn: (x0: V0, x1: V1, x2: V2, x3: V3) => T,
  args: [V0, V1],
): (x2: V2, x3: V3) => T;
partial<V0, V1, V2, V3, T>(
  fn: (x0: V0, x1: V1, x2: V2, x3: V3) => T,
  args: [V0],
): (x1: V1, x2: V2, x3: V3) => T;
partial<T>(fn: (...a: any[]) => T, args: any[]): (...a: any[]) => T;

import { isArray } from './_internals/isArray.js'

export function partial(fn, ...args){
  const len = fn.length

  // If a single array argument is given, those are the args (a la Ramda).
  // Otherwise, the variadic arguments are the args.
  const argList = args.length === 1 && isArray(args[0]) ? args[0] : args

  return (...rest) => {
    if (argList.length + rest.length >= len){
      return fn(...argList, ...rest)
    }

    return partial(fn, ...[ ...argList, ...rest ])
  }
}

import { partial } from './partial.js'
import { type } from './type.js'

const greet = (
  salutation, title, firstName, lastName
) =>
  [salutation, title, firstName, lastName]

test('happy', () => {
  const canPassAnyNumberOfArguments = partial(
    greet, 'Hello', 'Ms.'
  )
  const fn = canPassAnyNumberOfArguments('foo')
  const sayHello = partial(greet, [ 'Hello' ])
  const sayHelloRamda = partial(sayHello, [ 'Ms.' ])

  expect(type(fn)).toBe('Function')

  expect(fn('bar')).toStrictEqual(['Hello', 'Ms.', 'foo', 'bar'])
  expect(sayHelloRamda('foo', 'bar')).toStrictEqual(['Hello', 'Ms.', 'foo', 'bar'])
})

test('extra arguments are ignored', () => {
  const canPassAnyNumberOfArguments = partial(
    greet, 'Hello', 'Ms.'
  )
  const fn = canPassAnyNumberOfArguments('foo')

  expect(type(fn)).toBe('Function')

  expect(fn(
    'bar', 1, 2
  )).toStrictEqual(['Hello', 'Ms.', 'foo', 'bar'])
})

test('when array is input', () => {
  const fooFn = (
    a, b, c, d
  ) => ({
    a,
    b,
    c,
    d,
  })
  const barFn = partial(
    fooFn, [ 1, 2 ], []
  )

  expect(barFn(1, 2)).toEqual({
    a : [ 1, 2 ],
    b : [],
    c : 1,
    d : 2,
  })
})

test('ramda spec', () => {
  const sayHello = partial(greet, 'Hello')
  const sayHelloToMs = partial(sayHello, 'Ms.')

  expect(sayHelloToMs('Jane', 'Jones')).toStrictEqual(['Hello', 'Ms.', 'Jane', 'Jones'])
})

import {partial} from 'rambda'

describe('R.partial', () => {
  it('happy', () => {
    function fn(
      aString: string,
      aNumber: number,
      aBoolean: boolean,
      aNull: null
    ) {
      return {aString, aNumber, aBoolean, aNull}
    }

    // @ts-expect-error
    partial(fn, 1)

    const fn1 = partial(fn, ['a'])
    partial(fn1, ['b'])

    const fn2 = partial(fn1, [2])
    const result = fn2(true, null)
    result // $ExpectType { aString: string; aNumber: number; aBoolean: boolean; aNull: null; }
  })
})

partialObject


partialObject<Input, PartialInput, Output>(
  fn: (input: Input) => Output, 
  partialInput: PartialInput,
): (input: Pick<Input, Exclude<keyof Input, keyof PartialInput>>) => Output

R.partialObject is a curry helper designed specifically for functions accepting object as a single argument.

Initially the function knows only a part from the whole input object and then R.partialObject helps in preparing the function for the second part, when it receives the rest of the input.

Try this R.partialObject example in Rambda REPL

partialObject<Input, PartialInput, Output>(
  fn: (input: Input) => Output, 
  partialInput: PartialInput,
): (input: Pick<Input, Exclude<keyof Input, keyof PartialInput>>) => Output;

import { mergeDeepRight } from './mergeDeepRight.js'

export function partialObject(fn, input){
  return nextInput => fn(mergeDeepRight(nextInput, input))
}

import { delay } from './delay.js'
import { partialObject } from './partialObject.js'
import { type } from './type.js'

test('with plain function', () => {
  const fn = ({ a, b, c }) => a + b + c
  const curried = partialObject(fn, { a : 1 })

  expect(type(curried)).toBe('Function')
  expect(curried({
    b : 2,
    c : 3,
  })).toBe(6)
})

test('with function that throws an error', () => {
  const fn = ({ a, b, c }) => {
    throw new Error('foo')
  }
  const curried = partialObject(fn, { a : 1 })

  expect(type(curried)).toBe('Function')
  expect(() =>
    curried({
      b : 2,
      c : 3,
    })).toThrowErrorMatchingInlineSnapshot('"foo"')
})

test('with async', async () => {
  const fn = async ({ a, b, c }) => {
    await delay(100)

    return a + b + c
  }

  const curried = partialObject(fn, { a : 1 })

  const result = await curried({
    b : 2,
    c : 3,
  })

  expect(result).toBe(6)
})

test('async function throwing an error', async () => {
  const fn = async ({ a, b, c }) => {
    await delay(100)
    throw new Error('foo')
  }

  const curried = partialObject(fn, { a : 1 })

  try {
    await curried({
      b : 2,
      c : 3,
    })
    expect(true).toBeFalsy()
  } catch (e){
    expect(e.message).toBe('foo')
  }
})

import {partialObject, delay} from 'rambda'

describe('R.partialObject', () => {
  it('happy', () => {
    interface Input {
      a: number,
      b: number,
      c: string,
    }
    const fn = ({a, b, c}: Input) => a + b + c
    const curried = partialObject(fn, {a: 1})
    const result = curried({
      b: 2,
      c: 'foo',
    })
    result // $ExpectType string
  })
  it('asynchronous', async() => {
    interface Input {
      a: number,
      b: number,
      c: string,
    }
    const fn = async({a, b, c}: Input) => {
      await delay(100)
      return a + b + c
    }
    const curried = partialObject(fn, {a: 1})
    const result = await curried({
      b: 2,
      c: 'foo',
    })
    result // $ExpectType string
  })
})

partition


partition<T>(
  predicate: Predicate<T>,
  input: T[]
): [T[], T[]]

It will return array of two objects/arrays according to predicate function. The first member holds all instances of input that pass the predicate function, while the second member - those who doesn't.

Try this R.partition example in Rambda REPL

partition<T>(
  predicate: Predicate<T>,
  input: T[]
): [T[], T[]];
partition<T>(
  predicate: Predicate<T>
): (input: T[]) => [T[], T[]];
partition<T>(
  predicate: (x: T, prop?: string) => boolean,
  input: { [key: string]: T}
): [{ [key: string]: T}, { [key: string]: T}];
partition<T>(
  predicate: (x: T, prop?: string) => boolean
): (input: { [key: string]: T}) => [{ [key: string]: T}, { [key: string]: T}];

import { isArray } from './_internals/isArray.js'

export function partitionObject(predicate, iterable){
  const yes = {}
  const no = {}
  Object.entries(iterable).forEach(([ prop, value ]) => {
    if (predicate(value, prop)){
      yes[ prop ] = value
    } else {
      no[ prop ] = value
    }
  })

  return [ yes, no ]
}

export function partitionArray(
  predicate, list, indexed = false
){
  const yes = []
  const no = []
  let counter = -1

  while (counter++ < list.length - 1){
    if (
      indexed ? predicate(list[ counter ], counter) : predicate(list[ counter ])
    ){
      yes.push(list[ counter ])
    } else {
      no.push(list[ counter ])
    }
  }

  return [ yes, no ]
}

export function partition(predicate, iterable){
  if (arguments.length === 1){
    return listHolder => partition(predicate, listHolder)
  }
  if (!isArray(iterable)) return partitionObject(predicate, iterable)

  return partitionArray(predicate, iterable)
}

import { partition } from './partition.js'

test('with array', () => {
  const predicate = x => x > 2
  const list = [ 1, 2, 3, 4 ]

  const result = partition(predicate, list)
  const expectedResult = [
    [ 3, 4 ],
    [ 1, 2 ],
  ]

  expect(result).toEqual(expectedResult)
})

test('with object', () => {
  const predicate = (value, prop) => {
    expect(typeof prop).toBe('string')

    return value > 2
  }
  const hash = {
    a : 1,
    b : 2,
    c : 3,
    d : 4,
  }

  const result = partition(predicate)(hash)
  const expectedResult = [
    {
      c : 3,
      d : 4,
    },
    {
      a : 1,
      b : 2,
    },
  ]

  expect(result).toEqual(expectedResult)
})

test('readme example', () => {
  const list = [ 1, 2, 3 ]
  const obj = {
    a : 1,
    b : 2,
    c : 3,
  }
  const predicate = x => x > 2

  const result = [ partition(predicate, list), partition(predicate, obj) ]
  const expected = [
    [ [ 3 ], [ 1, 2 ] ],
    [
      { c : 3 },
      {
        a : 1,
        b : 2,
      },
    ],
  ]
  expect(result).toEqual(expected)
})

import {partition} from 'rambda'

describe('R.partition', () => {
  it('with array', () => {
    const predicate = (x: number) => {
      return x > 2
    }
    const list = [1, 2, 3, 4]

    const result = partition(predicate, list)
    const curriedResult = partition(predicate)(list)
    result // $ExpectType [number[], number[]]
    curriedResult // $ExpectType [number[], number[]]
  })

  /*
    revert to old version of `dtslint` and `R.partition` typing
    as there is diff between VSCode types(correct) and dtslint(incorrect)
    
    it('with object', () => {
      const predicate = (value: number, prop?: string) => {
        return value > 2
      }
      const hash = {
        a: 1,
        b: 2,
        c: 3,
        d: 4,
      }
  
      const result = partition(predicate, hash)
      const curriedResult = partition(predicate)(hash)
      result[0] // $xExpectType { [key: string]: number; }
      result[1] // $xExpectType { [key: string]: number; }
      curriedResult[0] // $xExpectType { [key: string]: number; }
      curriedResult[1] // $xExpectType { [key: string]: number; }
    })
    */
})

path


path<S, K0 extends keyof S = keyof S>(path: [K0], obj: S): S[K0]

If pathToSearch is 'a.b' then it will return 1 if obj is {a:{b:1}}.

It will return undefined, if such path is not found.

Try this R.path example in Rambda REPL

path<S, K0 extends keyof S = keyof S>(path: [K0], obj: S): S[K0];
path<S, K0 extends keyof S = keyof S, K1 extends keyof S[K0] = keyof S[K0]>(path: [K0, K1], obj: S): S[K0][K1];
path<
    S,
    K0 extends keyof S = keyof S,
    K1 extends keyof S[K0] = keyof S[K0],
    K2 extends keyof S[K0][K1] = keyof S[K0][K1]
>(path: [K0, K1, K2], obj: S): S[K0][K1][K2];
path<
    S,
    K0 extends keyof S = keyof S,
    K1 extends keyof S[K0] = keyof S[K0],
    K2 extends keyof S[K0][K1] = keyof S[K0][K1],
    K3 extends keyof S[K0][K1][K2] = keyof S[K0][K1][K2],
>(path: [K0, K1, K2, K3], obj: S): S[K0][K1][K2][K3];
path<
    S,
    K0 extends keyof S = keyof S,
    K1 extends keyof S[K0] = keyof S[K0],
    K2 extends keyof S[K0][K1] = keyof S[K0][K1],
    K3 extends keyof S[K0][K1][K2] = keyof S[K0][K1][K2],
    K4 extends keyof S[K0][K1][K2][K3] = keyof S[K0][K1][K2][K3],
>(path: [K0, K1, K2, K3, K4], obj: S): S[K0][K1][K2][K3][K4];
path<
    S,
    K0 extends keyof S = keyof S,
    K1 extends keyof S[K0] = keyof S[K0],
    K2 extends keyof S[K0][K1] = keyof S[K0][K1],
    K3 extends keyof S[K0][K1][K2] = keyof S[K0][K1][K2],
    K4 extends keyof S[K0][K1][K2][K3] = keyof S[K0][K1][K2][K3],
    K5 extends keyof S[K0][K1][K2][K3][K4] = keyof S[K0][K1][K2][K3][K4],
>(path: [K0, K1, K2, K3, K4, K5], obj: S): S[K0][K1][K2][K3][K4][K5];
path<T>(pathToSearch: string, obj: any): T | undefined;
path<T>(pathToSearch: string): (obj: any) => T | undefined;
path<T>(pathToSearch: RamdaPath): (obj: any) => T | undefined;
path<T>(pathToSearch: RamdaPath, obj: any): T | undefined;

import { createPath } from './_internals/createPath.js'

export function pathFn(pathInput, obj){
  let willReturn = obj
  let counter = 0

  const pathArrValue = createPath(pathInput)

  while (counter < pathArrValue.length){
    if (willReturn === null || willReturn === undefined){
      return undefined
    }
    if (willReturn[ pathArrValue[ counter ] ] === null) return undefined

    willReturn = willReturn[ pathArrValue[ counter ] ]
    counter++
  }

  return willReturn
}

export function path(pathInput, obj){
  if (arguments.length === 1) return _obj => path(pathInput, _obj)

  if (obj === null || obj === undefined){
    return undefined
  }

  return pathFn(pathInput, obj)
}

import { path } from './path.js'

test('with array inside object', () => {
  const obj = { a : { b : [ 1, { c : 1 } ] } }

  expect(path('a.b.1.c', obj)).toBe(1)
})

test('works with undefined', () => {
  const obj = { a : { b : { c : 1 } } }

  expect(path('a.b.c.d.f', obj)).toBeUndefined()
  expect(path('foo.babaz', undefined)).toBeUndefined()
  expect(path('foo.babaz')(undefined)).toBeUndefined()
})

test('works with string instead of array', () => {
  expect(path('foo.bar.baz')({ foo : { bar : { baz : 'yes' } } })).toBe('yes')
})

test('path', () => {
  expect(path([ 'foo', 'bar', 'baz' ])({ foo : { bar : { baz : 'yes' } } })).toBe('yes')

  expect(path([ 'foo', 'bar', 'baz' ])(null)).toBeUndefined()

  expect(path([ 'foo', 'bar', 'baz' ])({ foo : { bar : 'baz' } })).toBeUndefined()
})

test('null is not a valid path', () => {
  expect(path('audio_tracks', {
    a            : 1,
    audio_tracks : null,
  })).toBeUndefined()
})

import {path} from 'rambda'

const input = {a: {b: {c: true}}}

describe('R.path with string as path', () => {
  it('without specified output type', () => {
    // $ExpectType unknown
    path('a.b.c', input)
    // $ExpectType unknown
    path('a.b.c')(input)
  })
  it('with specified output type', () => {
    // $ExpectType boolean | undefined
    path<boolean>('a.b.c', input)
    // $ExpectType boolean | undefined
    path<boolean>('a.b.c')(input)
  })
})

describe('R.path with list as path', () => {
  it('with array as path', () => {
    // $ExpectType boolean
    path(['a', 'b', 'c'], input)
    // $ExpectType unknown
    path(['a', 'b', 'c'])(input)
  })
  test('shallow property', () => {
    // $ExpectType number
    path(['a'], {a: 1})

    // $ExpectType unknown
    path(['b'], {a: 1})
  })
  test('deep property', () => {
    const testObject = {a: {b: {c: {d: {e: {f: 1}}}}}}
    const result = path(['a', 'b', 'c', 'd', 'e', 'f'], testObject)
    // $ExpectType number
    result
    const curriedResult = path(['a', 'b', 'c', 'd', 'e', 'f'])(testObject)
    // $ExpectType unknown
    curriedResult
  })
  test('issue #668 - path is not correct', () => {
    const object = {
      is: {
        a: 'path',
      },
    }
    const result = path(['is', 'not', 'a'], object)
    // $ExpectType unknown
    result
    const curriedResult = path(['is', 'not', 'a'])(object)
    // $ExpectType unknown
    curriedResult
  })
})

pathEq


pathEq(pathToSearch: Path, target: any, input: any): boolean

It returns true if pathToSearch of input object is equal to target value.

pathToSearch is passed to R.path, which means that it can be either a string or an array. Also equality between target and the found value is determined by R.equals.

Try this R.pathEq example in Rambda REPL

pathEq(pathToSearch: Path, target: any, input: any): boolean;
pathEq(pathToSearch: Path, target: any): (input: any) => boolean;
pathEq(pathToSearch: Path): (target: any) => (input: any) => boolean;

import { curry } from './curry.js'
import { equals } from './equals.js'
import { path } from './path.js'

function pathEqFn(
  pathToSearch, target, input
){
  return equals(path(pathToSearch, input), target)
}

export const pathEq = curry(pathEqFn)

import { pathEq } from './pathEq.js'

test('when true', () => {
  const path = 'a.b'
  const obj = { a : { b : { c : 1 } } }
  const target = { c : 1 }

  expect(pathEq(
    path, target, obj
  )).toBeTrue()
})

test('when false', () => {
  const path = 'a.b'
  const obj = { a : { b : 1 } }
  const target = 2

  expect(pathEq(path, target)(obj)).toBeFalse()
})

test('when wrong path', () => {
  const path = 'foo.bar'
  const obj = { a : { b : 1 } }
  const target = 2

  expect(pathEq(
    path, target, obj
  )).toBeFalse()
})

import {pathEq} from 'rambda'

describe('R.pathEq', () => {
  it('with string path', () => {
    const pathToSearch = 'a.b.c'
    const input = {a: {b: {c: 1}}}
    const target = {c: 1}

    const result = pathEq(pathToSearch, input, target)
    const curriedResult = pathEq(pathToSearch, input, target)
    result // $ExpectType boolean
    curriedResult // $ExpectType boolean
  })

  it('with array path', () => {
    const pathToSearch = ['a', 'b', 'c']
    const input = {a: {b: {c: 1}}}
    const target = {c: 1}

    const result = pathEq(pathToSearch, input, target)
    const curriedResult = pathEq(pathToSearch, input, target)
    result // $ExpectType boolean
    curriedResult // $ExpectType boolean
  })
})

describe('with ramda specs', () => {
  const testPath = ['x', 0, 'y']
  const testObj = {
    x: [
      {y: 2, z: 3},
      {y: 4, z: 5},
    ],
  }

  const result1 = pathEq(testPath, 2, testObj)
  const result2 = pathEq(testPath, 2)(testObj)
  const result3 = pathEq(testPath)(2)(testObj)
  result1 // $ExpectType boolean
  result2 // $ExpectType boolean
  result3 // $ExpectType boolean
})

pathOr


pathOr<T>(defaultValue: T, pathToSearch: Path, obj: any): T

It reads obj input and returns either R.path(pathToSearch, Record<string, unknown>) result or defaultValue input.

Try this R.pathOr example in Rambda REPL

pathOr<T>(defaultValue: T, pathToSearch: Path, obj: any): T;
pathOr<T>(defaultValue: T, pathToSearch: Path): (obj: any) => T;
pathOr<T>(defaultValue: T): (pathToSearch: Path) => (obj: any) => T;

import { curry } from './curry.js'
import { defaultTo } from './defaultTo.js'
import { path } from './path.js'

function pathOrFn(
  defaultValue, pathInput, obj
){
  return defaultTo(defaultValue, path(pathInput, obj))
}

export const pathOr = curry(pathOrFn)

import { pathOr } from './pathOr.js'

test('with undefined', () => {
  const result = pathOr(
    'foo', 'x.y', { x : { y : 1 } }
  )

  expect(result).toBe(1)
})

test('with null', () => {
  const result = pathOr(
    'foo', 'x.y', null
  )

  expect(result).toBe('foo')
})

test('with NaN', () => {
  const result = pathOr(
    'foo', 'x.y', NaN
  )

  expect(result).toBe('foo')
})

test('curry case (x)(y)(z)', () => {
  const result = pathOr('foo')('x.y.z')({ x : { y : { a : 1 } } })

  expect(result).toBe('foo')
})

test('curry case (x)(y,z)', () => {
  const result = pathOr('foo', 'x.y.z')({ x : { y : { a : 1 } } })

  expect(result).toBe('foo')
})

test('curry case (x,y)(z)', () => {
  const result = pathOr('foo')('x.y.z', { x : { y : { a : 1 } } })

  expect(result).toBe('foo')
})

import {pathOr} from 'rambda'

describe('R.pathOr', () => {
  it('with string path', () => {
    const x = pathOr<string>('foo', 'x.y', {x: {y: 'bar'}})
    x // $ExpectType string
  })
  it('with array path', () => {
    const x = pathOr<string>('foo', ['x', 'y'], {x: {y: 'bar'}})
    x // $ExpectType string
  })
  it('without passing type looks bad', () => {
    const x = pathOr('foo', 'x.y', {x: {y: 'bar'}})
    x // $ExpectType "foo"
  })
  it('curried', () => {
    const x = pathOr<string>('foo', 'x.y')({x: {y: 'bar'}})
    x // $ExpectType string
  })
})

paths


paths<Input, T>(pathsToSearch: Path[], obj: Input): (T | undefined)[]

It loops over members of pathsToSearch as singlePath and returns the array produced by R.path(singlePath, Record<string, unknown>).

Because it calls R.path, then singlePath can be either string or a list.

Try this R.paths example in Rambda REPL

paths<Input, T>(pathsToSearch: Path[], obj: Input): (T | undefined)[];
paths<Input, T>(pathsToSearch: Path[]): (obj: Input) => (T | undefined)[];
paths<T>(pathsToSearch: Path[], obj: any): (T | undefined)[];
paths<T>(pathsToSearch: Path[]): (obj: any) => (T | undefined)[];

import { path } from './path.js'

export function paths(pathsToSearch, obj){
  if (arguments.length === 1){
    return _obj => paths(pathsToSearch, _obj)
  }

  return pathsToSearch.map(singlePath => path(singlePath, obj))
}

import { paths } from './paths.js'

const obj = {
  a : {
    b : {
      c : 1,
      d : 2,
    },
  },
  p : [ { q : 3 } ],
  x : {
    y : 'FOO',
    z : [ [ {} ] ],
  },
}

test('with string path + curry', () => {
  const pathsInput = [ 'a.b.d', 'p.q' ]
  const expected = [ 2, undefined ]
  const result = paths(pathsInput, obj)
  const curriedResult = paths(pathsInput)(obj)

  expect(result).toEqual(expected)
  expect(curriedResult).toEqual(expected)
})

test('with array path', () => {
  const result = paths([
    [ 'a', 'b', 'c' ],
    [ 'x', 'y' ],
  ],
  obj)

  expect(result).toEqual([ 1, 'FOO' ])
})

test('takes a paths that contains indices into arrays', () => {
  expect(paths([
    [ 'p', 0, 'q' ],
    [ 'x', 'z', 0, 0 ],
  ],
  obj)).toEqual([ 3, {} ])
  expect(paths([
    [ 'p', 0, 'q' ],
    [ 'x', 'z', 2, 1 ],
  ],
  obj)).toEqual([ 3, undefined ])
})

test('gets a deep property\'s value from objects', () => {
  expect(paths([ [ 'a', 'b' ] ], obj)).toEqual([ obj.a.b ])
  expect(paths([ [ 'p', 0 ] ], obj)).toEqual([ obj.p[ 0 ] ])
})

test('returns undefined for items not found', () => {
  expect(paths([ [ 'a', 'x', 'y' ] ], obj)).toEqual([ undefined ])
  expect(paths([ [ 'p', 2 ] ], obj)).toEqual([ undefined ])
})

import {paths} from 'rambda'

interface Input {
  a: number,
  b: number,
  c: number,
}

const input: Input = {a: 1, b: 2, c: 3}

describe('R.paths', () => {
  it('with dot notation', () => {
    const result = paths<number>(['a.b.c', 'foo.bar'], input)
    result // $ExpectType (number | undefined)[]
  })

  it('without type', () => {
    const result = paths(['a.b.c', 'foo.bar'], input)
    result // $ExpectType unknown[]
  })

  it('with array as path', () => {
    const result = paths<number>([['a', 'b', 'c'], ['foo.bar']], input)
    result // $ExpectType (number | undefined)[]
  })

  it('curried', () => {
    const result = paths<number>([['a', 'b', 'c'], ['foo.bar']])(input)
    result // $ExpectType (number | undefined)[]
  })
})

pathSatisfies

Try this R.pathSatisfies example in Rambda REPL

pick


pick<T, K extends string | number | symbol>(propsToPick: K[], input: T): Pick<T, Exclude<keyof T, Exclude<keyof T, K>>>

It returns a partial copy of an input containing only propsToPick properties.

input can be either an object or an array.

String annotation of propsToPick is one of the differences between Rambda and Ramda.

Try this R.pick example in Rambda REPL

pick<T, K extends string | number | symbol>(propsToPick: K[], input: T): Pick<T, Exclude<keyof T, Exclude<keyof T, K>>>;
pick<K extends string | number | symbol>(propsToPick: K[]): <T>(input: T) => Pick<T, Exclude<keyof T, Exclude<keyof T, K>>>;
pick<T, U>(propsToPick: string, input: T): U;
pick<T, U>(propsToPick: string): (input: T) => U;
pick<T>(propsToPick: string, input: object): T;
pick<T>(propsToPick: string): (input: object) => T;

import { createPath } from './_internals/createPath.js'

export function pick(propsToPick, input){
  if (arguments.length === 1) return _input => pick(propsToPick, _input)

  if (input === null || input === undefined){
    return undefined
  }
  const keys = createPath(propsToPick, ',')
  const willReturn = {}
  let counter = 0

  while (counter < keys.length){
    if (keys[ counter ] in input){
      willReturn[ keys[ counter ] ] = input[ keys[ counter ] ]
    }
    counter++
  }

  return willReturn
}

import { pick } from './pick.js'

const obj = {
  a : 1,
  b : 2,
  c : 3,
}

test('props to pick is a string', () => {
  const result = pick('a,c', obj)
  const resultCurry = pick('a,c')(obj)
  const expectedResult = {
    a : 1,
    c : 3,
  }

  expect(result).toEqual(expectedResult)
  expect(resultCurry).toEqual(expectedResult)
})

test('when prop is missing', () => {
  const result = pick('a,d,f', obj)
  expect(result).toEqual({ a : 1 })
})

test('with list indexes as props', () => {
  const list = [ 1, 2, 3 ]
  const expected = {
    0 : 1,
    2 : 3,
  }
  expect(pick([ 0, 2, 3 ], list)).toEqual(expected)
  expect(pick('0,2,3', list)).toEqual(expected)
})

test('props to pick is an array', () => {
  expect(pick([ 'a', 'c' ])({
    a : 'foo',
    b : 'bar',
    c : 'baz',
  })).toEqual({
    a : 'foo',
    c : 'baz',
  })

  expect(pick([ 'a', 'd', 'e', 'f' ])({
    a : 'foo',
    b : 'bar',
    c : 'baz',
  })).toEqual({ a : 'foo' })

  expect(pick('a,d,e,f')(null)).toBeUndefined()
})

test('works with list as input and number as props - props to pick is an array', () => {
  const result = pick([ 1, 2 ], [ 'a', 'b', 'c', 'd' ])
  expect(result).toEqual({
    1 : 'b',
    2 : 'c',
  })
})

test('works with list as input and number as props - props to pick is a string', () => {
  const result = pick('1,2', [ 'a', 'b', 'c', 'd' ])
  expect(result).toEqual({
    1 : 'b',
    2 : 'c',
  })
})

test('with symbol', () => {
  const symbolProp = Symbol('s')
  expect(pick([ symbolProp ], { [ symbolProp ] : 'a' })).toMatchInlineSnapshot(`
{
  Symbol(s): "a",
}
`)
})

import {pick} from 'rambda'

const input = {a: 'foo', b: 2, c: 3, d: 4}

describe('R.pick with array as props input', () => {
  it('without passing type', () => {
    const result = pick(['a', 'c'], input)
    result.a // $ExpectType string
    result.c // $ExpectType number
  })
})

describe('R.pick with string as props input', () => {
  interface Input {
    a: string,
    b: number,
    c: number,
    d: number,
  }
  interface Output {
    a: string,
    c: number,
  }
  it('explicitly declare output', () => {
    const result = pick<Output>('a,c', input)
    result // $ExpectType Output
    result.a // $ExpectType string
    result.c // $ExpectType number

    const curriedResult = pick<Output>('a,c')(input)

    curriedResult.a // $ExpectType string
  })

  it('explicitly declare input and output', () => {
    const result = pick<Input, Output>('a,c', input)
    result // $ExpectType Output
    result.a // $ExpectType string

    const curriedResult = pick<Input, Output>('a,c')(input)

    curriedResult.a // $ExpectType string
  })

  it('without passing type', () => {
    const result = pick('a,c', input)
    result // $ExpectType unknown
  })
})

pickAll


pickAll<T, K extends keyof T>(propsToPicks: K[], input: T): Pick<T, K>

Same as R.pick but it won't skip the missing props, i.e. it will assign them to undefined.

Try this R.pickAll example in Rambda REPL

pickAll<T, K extends keyof T>(propsToPicks: K[], input: T): Pick<T, K>;
pickAll<T, U>(propsToPicks: string[], input: T): U;
pickAll(propsToPicks: string[]): <T, U>(input: T) => U;
pickAll<T, U>(propsToPick: string, input: T): U;
pickAll<T, U>(propsToPick: string): (input: T) => U;

import { createPath } from './_internals/createPath.js'

export function pickAll(propsToPick, obj){
  if (arguments.length === 1) return _obj => pickAll(propsToPick, _obj)

  if (obj === null || obj === undefined){
    return undefined
  }
  const keysValue = createPath(propsToPick, ',')
  const willReturn = {}
  let counter = 0

  while (counter < keysValue.length){
    if (keysValue[ counter ] in obj){
      willReturn[ keysValue[ counter ] ] = obj[ keysValue[ counter ] ]
    } else {
      willReturn[ keysValue[ counter ] ] = undefined
    }
    counter++
  }

  return willReturn
}

import { pickAll } from './pickAll.js'

test('when input is undefined or null', () => {
  expect(pickAll('a', null)).toBeUndefined()
  expect(pickAll('a', undefined)).toBeUndefined()
})

test('with string as condition', () => {
  const obj = {
    a : 1,
    b : 2,
    c : 3,
  }
  const result = pickAll('a,c', obj)
  const resultCurry = pickAll('a,c')(obj)
  const expectedResult = {
    a : 1,
    b : undefined,
    c : 3,
  }

  expect(result).toEqual(expectedResult)
  expect(resultCurry).toEqual(expectedResult)
})

test('with array as condition', () => {
  expect(pickAll([ 'a', 'b', 'c' ], {
    a : 'foo',
    c : 'baz',
  })).toEqual({
    a : 'foo',
    b : undefined,
    c : 'baz',
  })
})

import {pickAll} from 'rambda'

interface Input {
  a: string,
  b: number,
  c: number,
  d: number,
}
interface Output {
  a?: string,
  c?: number,
}
const input = {a: 'foo', b: 2, c: 3, d: 4}

describe('R.pickAll with array as props input', () => {
  it('without passing type', () => {
    const result = pickAll(['a', 'c'], input)
    result.a // $ExpectType string
    result.c // $ExpectType number
  })
  it('without passing type + curry', () => {
    const result = pickAll(['a', 'c'])(input)
    result // $ExpectType unknown
  })
  it('explicitly passing types', () => {
    const result = pickAll<Input, Output>(['a', 'c'], input)
    result.a // $ExpectType string | undefined
    result.c // $ExpectType number | undefined
  })
})

describe('R.pickAll with string as props input', () => {
  it('without passing type', () => {
    const result = pickAll('a,c', input)
    result // $ExpectType unknown
  })
  it('without passing type + curry', () => {
    const result = pickAll('a,c')(input)
    result // $ExpectType unknown
  })
  it('explicitly passing types', () => {
    const result = pickAll<Input, Output>('a,c', input)
    result.a // $ExpectType string | undefined
    result.c // $ExpectType number | undefined
  })
  it('explicitly passing types + curry', () => {
    const result = pickAll<Input, Output>('a,c')(input)
    result.a // $ExpectType string | undefined
    result.c // $ExpectType number | undefined
  })
})

pickBy

Try this R.pickBy example in Rambda REPL

pipe

It performs left-to-right function composition.

Try this R.pipe example in Rambda REPL

pluck


pluck<K extends keyof T, T>(property: K, list: T[]): T[K][]

It returns list of the values of property taken from the all objects inside list.

Try this R.pluck example in Rambda REPL

pluck<K extends keyof T, T>(property: K, list: T[]): T[K][];
pluck<T>(property: number, list: { [k: number]: T }[]):  T[];
pluck<P extends string>(property: P): <T>(list: Record<P, T>[]) => T[];
pluck(property: number): <T>(list: { [k: number]: T }[]) => T[];

import { map } from './map.js'

export function pluck(property, list){
  if (arguments.length === 1) return _list => pluck(property, _list)

  const willReturn = []

  map(x => {
    if (x[ property ] !== undefined){
      willReturn.push(x[ property ])
    }
  }, list)

  return willReturn
}

import { pluck } from './pluck.js'

test('happy', () => {
  expect(pluck('a')([ { a : 1 }, { a : 2 }, { b : 1 } ])).toEqual([ 1, 2 ])
})

test('with undefined', () => {
  expect(pluck(undefined)([ { a : 1 }, { a : 2 }, { b : 1 } ])).toEqual([ ])
})

test('with number', () => {
  const input = [
    [ 1, 2 ],
    [ 3, 4 ],
  ]

  expect(pluck(0, input)).toEqual([ 1, 3 ])
})

import {pluck} from 'rambda'

describe('R.pluck', () => {
  it('with object', () => {
    interface ListMember {
      a: number,
      b: string,
    }
    const input: ListMember[] = [
      {a: 1, b: 'foo'},
      {a: 2, b: 'bar'},
    ]
    const resultA = pluck('a', input)
    const resultB = pluck('b')(input)
    resultA // $ExpectType number[]
    resultB // $ExpectType string[]
  })

  it('with array', () => {
    const input = [
      [1, 2],
      [3, 4],
      [5, 6],
    ]
    const result = pluck(0, input)
    const resultCurry = pluck(0)(input)
    result // $ExpectType number[]
    resultCurry // $ExpectType number[]
  })
})

prepend


prepend<T>(xToPrepend: T, iterable: T[]): T[]

It adds element x at the beginning of list.

Try this R.prepend example in Rambda REPL

prepend<T>(xToPrepend: T, iterable: T[]): T[];
prepend<T, U>(xToPrepend: T, iterable: IsFirstSubtypeOfSecond<T, U>[]) : U[];
prepend<T>(xToPrepend: T): <U>(iterable: IsFirstSubtypeOfSecond<T, U>[]) => U[];
prepend<T>(xToPrepend: T): (iterable: T[]) => T[];

export function prepend(x, input){
  if (arguments.length === 1) return _input => prepend(x, _input)

  if (typeof input === 'string') return [ x ].concat(input.split(''))

  return [ x ].concat(input)
}

import { prepend } from './prepend.js'

test('happy', () => {
  expect(prepend('yes', [ 'foo', 'bar', 'baz' ])).toEqual([
    'yes',
    'foo',
    'bar',
    'baz',
  ])
})

test('with empty list', () => {
  expect(prepend('foo')([])).toEqual([ 'foo' ])
})

test('with string instead of array', () => {
  expect(prepend('foo')('bar')).toEqual([ 'foo', 'b', 'a', 'r' ])
})

product


product(list: number[]): number

Try this R.product example in Rambda REPL

product(list: number[]): number;

import { multiply } from './multiply.js'
import { reduce } from './reduce.js'

export const product = reduce(multiply, 1)

import { product } from './product.js'

test('happy', () => {
  expect(product([ 2, 3, 4 ])).toBe(24)
})

test('bad input', () => {
  expect(product([ null ])).toBe(0)
  expect(product([])).toBe(1)
})

import {product} from 'rambda'

describe('R.product', () => {
  it('happy', () => {
    const result = product([1, 2, 3])

    result // $ExpectType number
  })
})

prop


prop<_, P extends keyof never, T>(p: P, value: T): Prop<T, P>

It returns the value of property propToFind in obj.

If there is no such property, it returns undefined.

Try this R.prop example in Rambda REPL

prop<_, P extends keyof never, T>(p: P, value: T): Prop<T, P>;
prop<V>(p: keyof never, value: unknown): V;
prop<_, P extends keyof never>(p: P): <T>(value: T) => Prop<T, P>;
prop<V>(p: keyof never): (value: unknown) => V;

export function propFn(searchProperty, obj){
  if (!obj) return undefined

  return obj[ searchProperty ]
}

export function prop(searchProperty, obj){
  if (arguments.length === 1) return _obj => prop(searchProperty, _obj)

  return propFn(searchProperty, obj)
}

import { prop } from './prop.js'

test('prop', () => {
  expect(prop('foo')({ foo : 'baz' })).toBe('baz')

  expect(prop('bar')({ foo : 'baz' })).toBeUndefined()

  expect(prop('bar')(null)).toBeUndefined()
})

import {prop} from 'rambda'

describe('R.prop', () => {
  interface Foo {
    a: number,
    b: string,
    c?: number,
  }
  const obj: Foo = {a: 1, b: 'foo'}

  it('issue #553', () => {
    const result = {
      a: prop('a', obj),
      b: prop('b', obj),
      c: prop('c', obj),
    }
    const curriedResult = {
      a: prop('a')(obj),
      b: prop('b')(obj),
      c: prop('c')(obj),
    }

    result // $ExpectType { a: number; b: string; c: number | undefined; }
    curriedResult // $ExpectType { a: number; b: string; c: number | undefined; }
  })
})

describe('with number as prop', () => {
  const list = [1, 2, 3]
  const index = 1
  it('happy', () => {
    const result = prop(index, list)

    result // $ExpectType number
  })
  it('curried require explicit type', () => {
    const result = prop<number>(index)(list)

    result // $ExpectType number
  })
})

propEq


propEq<K extends string | number>(valueToMatch: any, propToFind: K, obj: Record<K, any>): boolean

It returns true if obj has property propToFind and its value is equal to valueToMatch.

Try this R.propEq example in Rambda REPL

propEq<K extends string | number>(valueToMatch: any, propToFind: K, obj: Record<K, any>): boolean;
propEq<K extends string | number>(valueToMatch: any, propToFind: K): (obj: Record<K, any>) => boolean;
propEq(valueToMatch: any): {
  <K extends string | number>(propToFind: K, obj: Record<K, any>): boolean;
  <K extends string | number>(propToFind: K): (obj: Record<K, any>) => boolean;
};

import { curry } from './curry.js'
import { equals } from './equals.js'
import { prop } from './prop.js'

function propEqFn(
  valueToMatch, propToFind, obj
){
  if (!obj) return false

  return equals(valueToMatch, prop(propToFind, obj))
}

export const propEq = curry(propEqFn)

import { BAR, FOO } from './_internals/testUtils.js'
import { propEq } from './propEq.js'

test('happy', () => {
  const obj = { [ FOO ] : BAR }
  expect(propEq(BAR, FOO)(obj)).toBeTrue()
  expect(propEq(1, FOO)(obj)).toBeFalse()
  expect(propEq(1)(FOO)(obj)).toBeFalse()
  expect(propEq(
    1, 1, null
  )).toBeFalse()
})

test('returns false if called with a null or undefined object', () => {
  expect(propEq(
    'name', 'Abby', null
  )).toBeFalse()
  expect(propEq(
    'name', 'Abby', undefined
  )).toBeFalse()
})

import {propEq} from 'rambda'

const property = 'foo'
const numberProperty = 1
const value = 'bar'
const obj = {[property]: value}
const objWithNumberIndex = {[numberProperty]: value}

describe('R.propEq', () => {
  it('happy', () => {
    const result = propEq(value, property, obj)
    result // $ExpectType boolean
  })

  it('number is property', () => {
    const result = propEq(value, 1, objWithNumberIndex)
    result // $ExpectType boolean
  })

  it('with optional property', () => {
    interface MyType {
      optional?: string | number,
    }

    const myObject: MyType = {}
    const valueToFind = '1111'
    // @ts-expect-error
    propEq(valueToFind, 'optional', myObject)
  })

  it('imported from @types/ramda', () => {
    interface A {
      foo: string | null,
    }
    const obj: A = {
      foo: 'bar',
    }
    const value = ''
    const result = propEq(value, 'foo')(obj)
    result // $ExpectType boolean

    // @ts-expect-error
    propEq(value, 'bar')(obj)
  })
})

propIs


propIs<C extends AnyFunction, K extends keyof any>(type: C, name: K, obj: any): obj is Record<K, ReturnType<C>>

It returns true if property of obj is from target type.

Try this R.propIs example in Rambda REPL

propIs<C extends AnyFunction, K extends keyof any>(type: C, name: K, obj: any): obj is Record<K, ReturnType<C>>;
propIs<C extends AnyConstructor, K extends keyof any>(type: C, name: K, obj: any): obj is Record<K, InstanceType<C>>;
propIs<C extends AnyFunction, K extends keyof any>(type: C, name: K): (obj: any) => obj is Record<K, ReturnType<C>>;
propIs<C extends AnyConstructor, K extends keyof any>(type: C, name: K): (obj: any) => obj is Record<K, InstanceType<C>>;
propIs<C extends AnyFunction>(type: C): {
    <K extends keyof any>(name: K, obj: any): obj is Record<K, ReturnType<C>>;
    <K extends keyof any>(name: K): (obj: any) => obj is Record<K, ReturnType<C>>;
};

import { curry } from './curry.js'
import { is } from './is.js'

function propIsFn(
  targetPrototype, property, obj
){
  return is(targetPrototype, obj[ property ])
}

export const propIs = curry(propIsFn)

import { propIs } from './propIs.js'

const obj = {
  a : 1,
  b : 'foo',
}

test('when true', () => {
  expect(propIs(
    Number, 'a', obj
  )).toBeTrue()
  expect(propIs(
    String, 'b', obj
  )).toBeTrue()
})

test('when false', () => {
  expect(propIs(
    String, 'a', obj
  )).toBeFalse()
  expect(propIs(
    Number, 'b', obj
  )).toBeFalse()
})

import {propIs} from 'rambda'

const property = 'a'
const obj = {a: 1}

describe('R.propIs', () => {
  it('happy', () => {
    const result = propIs(Number, property, obj)
    result // $ExpectType boolean
  })

  it('curried', () => {
    const result = propIs(Number, property)(obj)
    result // $ExpectType boolean
  })
})

propOr


propOr<T, P extends string>(defaultValue: T, property: P, obj: Partial<Record<P, T>> | undefined): T

It returns either defaultValue or the value of property in obj.

Try this R.propOr example in Rambda REPL

propOr<T, P extends string>(defaultValue: T, property: P, obj: Partial<Record<P, T>> | undefined): T;
propOr<T, P extends string>(defaultValue: T, property: P): (obj: Partial<Record<P, T>> | undefined) => T;
propOr<T>(defaultValue: T): {
  <P extends string>(property: P, obj: Partial<Record<P, T>> | undefined): T;
  <P extends string>(property: P): (obj: Partial<Record<P, T>> | undefined) => T;
}

import { curry } from './curry.js'
import { defaultTo } from './defaultTo.js'

function propOrFn(
  defaultValue, property, obj
){
  if (!obj) return defaultValue

  return defaultTo(defaultValue, obj[ property ])
}

export const propOr = curry(propOrFn)

import { propOr } from './propOr.js'

test('propOr (result)', () => {
  const obj = { a : 1 }
  expect(propOr(
    'default', 'a', obj
  )).toBe(1)
  expect(propOr(
    'default', 'notExist', obj
  )).toBe('default')
  expect(propOr(
    'default', 'notExist', null
  )).toBe('default')
})

test('propOr (currying)', () => {
  const obj = { a : 1 }
  expect(propOr('default')('a', obj)).toBe(1)
  expect(propOr('default', 'a')(obj)).toBe(1)
  expect(propOr('default')('notExist', obj)).toBe('default')
  expect(propOr('default', 'notExist')(obj)).toBe('default')
})

import {propOr} from 'rambda'

const obj = {foo: 'bar'}
const property = 'foo'
const fallback = 'fallback'

describe('R.propOr', () => {
  it('happy', () => {
    const result = propOr(fallback, property, obj)
    result // $ExpectType string
  })
  it('curry 1', () => {
    const result = propOr(fallback)(property, obj)
    result // $ExpectType string
  })
  it('curry 2', () => {
    const result = propOr(fallback, property)(obj)
    result // $ExpectType string
  })
  it('curry 3', () => {
    const result = propOr(fallback)(property)(obj)
    result // $ExpectType string
  })
})

props


props<P extends string, T>(propsToPick: P[], obj: Record<P, T>): T[]

It takes list with properties propsToPick and returns a list with property values in obj.

Try this R.props example in Rambda REPL

props<P extends string, T>(propsToPick: P[], obj: Record<P, T>): T[];
props<P extends string>(propsToPick: P[]): <T>(obj: Record<P, T>) => T[];
props<P extends string, T>(propsToPick: P[]): (obj: Record<P, T>) => T[];

import { isArray } from './_internals/isArray.js'
import { mapArray } from './map.js'

export function props(propsToPick, obj){
  if (arguments.length === 1){
    return _obj => props(propsToPick, _obj)
  }
  if (!isArray(propsToPick)){
    throw new Error('propsToPick is not a list')
  }

  return mapArray(prop => obj[ prop ], propsToPick)
}

import { props } from './props.js'

const obj = {
  a : 1,
  b : 2,
}
const propsToPick = [ 'a', 'c' ]

test('happy', () => {
  const result = props(propsToPick, obj)
  expect(result).toEqual([ 1, undefined ])
})

test('curried', () => {
  const result = props(propsToPick)(obj)
  expect(result).toEqual([ 1, undefined ])
})

test('wrong input', () => {
  expect(() => props(null)(obj)).toThrowErrorMatchingInlineSnapshot('"propsToPick is not a list"')
})

import {props} from 'rambda'

const obj = {a: 1, b: 2}

describe('R.props', () => {
  it('happy', () => {
    const result = props(['a', 'b'], obj)

    result // $ExpectType number[]
  })
  it('curried', () => {
    const result = props(['a', 'b'])(obj)

    result // $ExpectType number[]
  })
})

propSatisfies


propSatisfies<T>(predicate: Predicate<T>, property: string, obj: Record<string, T>): boolean

It returns true if the object property satisfies a given predicate.

Try this R.propSatisfies example in Rambda REPL

propSatisfies<T>(predicate: Predicate<T>, property: string, obj: Record<string, T>): boolean;
propSatisfies<T>(predicate: Predicate<T>, property: string): (obj: Record<string, T>) => boolean;

import { curry } from './curry.js'
import { prop } from './prop.js'

function propSatisfiesFn(
  predicate, property, obj
){
  return predicate(prop(property, obj))
}

export const propSatisfies = curry(propSatisfiesFn)

import { propSatisfies } from './propSatisfies.js'

const obj = { a : 1 }

test('when true', () => {
  expect(propSatisfies(
    x => x > 0, 'a', obj
  )).toBeTrue()
})

test('when false', () => {
  expect(propSatisfies(x => x < 0, 'a')(obj)).toBeFalse()
})

import {propSatisfies} from 'rambda'

const obj = {a: 1}

describe('R.propSatisfies', () => {
  it('happy', () => {
    const result = propSatisfies(x => x > 0, 'a', obj)

    result // $ExpectType boolean
  })
  it('curried requires explicit type', () => {
    const result = propSatisfies<number>(x => x > 0, 'a')(obj)

    result // $ExpectType boolean
  })
})

range


range(startInclusive: number, endExclusive: number): number[]

It returns list of numbers between startInclusive to endExclusive markers.

Try this R.range example in Rambda REPL

range(startInclusive: number, endExclusive: number): number[];
range(startInclusive: number): (endExclusive: number) => number[];

export function range(start, end){
  if (arguments.length === 1) return _end => range(start, _end)

  if (Number.isNaN(Number(start)) || Number.isNaN(Number(end))){
    throw new TypeError('Both arguments to range must be numbers')
  }

  if (end < start) return []

  const len = end - start
  const willReturn = Array(len)

  for (let i = 0; i < len; i++){
    willReturn[ i ] = start + i
  }

  return willReturn
}

import { range } from './range.js'

test('happy', () => {
  expect(range(0, 10)).toEqual([ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 ])
})

test('end range is bigger than start range', () => {
  expect(range(7, 3)).toEqual([])
  expect(range(5, 5)).toEqual([])
})

test('with bad input', () => {
  const throwMessage = 'Both arguments to range must be numbers'
  expect(() => range('a', 6)).toThrowWithMessage(Error, throwMessage)
  expect(() => range(6, 'z')).toThrowWithMessage(Error, throwMessage)
})

test('curry', () => {
  expect(range(0)(10)).toEqual([ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 ])
})

import {range} from 'rambda'

describe('R.range', () => {
  it('happy', () => {
    const result = range(1, 4)

    result // $ExpectType number[]
  })
  it('curried', () => {
    const result = range(1)(4)

    result // $ExpectType number[]
  })
})

reduce

Try this R.reduce example in Rambda REPL

reduceBy

Try this R.reduceBy example in Rambda REPL

reject


reject<T>(predicate: Predicate<T>, list: T[]): T[]

It has the opposite effect of R.filter.

Try this R.reject example in Rambda REPL

reject<T>(predicate: Predicate<T>, list: T[]): T[];
reject<T>(predicate: Predicate<T>): (list: T[]) => T[];
reject<T>(predicate: Predicate<T>, obj: Dictionary<T>): Dictionary<T>;
reject<T, U>(predicate: Predicate<T>): (obj: Dictionary<T>) => Dictionary<T>;

import { filter } from './filter.js'

export function reject(predicate, list){
  if (arguments.length === 1) return _list => reject(predicate, _list)

  return filter(x => !predicate(x), list)
}

import { reject } from './reject.js'

const isOdd = n => n % 2 === 1

test('with array', () => {
  expect(reject(isOdd)([ 1, 2, 3, 4 ])).toEqual([ 2, 4 ])
})

test('with object', () => {
  const obj = {
    a : 1,
    b : 2,
    c : 3,
    d : 4,
  }
  expect(reject(isOdd, obj)).toEqual({
    b : 2,
    d : 4,
  })
})

import {reject} from 'rambda'

describe('R.reject with array', () => {
  it('happy', () => {
    const result = reject(
      x => {
        x // $ExpectType number
        return x > 1
      },
      [1, 2, 3]
    )
    result // $ExpectType number[]
  })
  it('curried require explicit type', () => {
    const result = reject<number>(x => {
      x // $ExpectType number
      return x > 1
    })([1, 2, 3])
    result // $ExpectType number[]
  })
})

describe('R.reject with objects', () => {
  it('happy', () => {
    const result = reject(
      x => {
        x // $ExpectType number

        return x > 1
      },
      {a: 1, b: 2}
    )
    result // $ExpectType Dictionary<number>
  })
  it('curried require dummy type', () => {
    const result = reject<number, any>(x => {
      return x > 1
    })({a: 1, b: 2})
    result // $ExpectType Dictionary<number>
  })
})

removeIndex


removeIndex<T>(index: number, list: T[]): T[]

It returns a copy of list input with removed index.

Try this R.removeIndex example in Rambda REPL

removeIndex<T>(index: number, list: T[]): T[];
removeIndex(index: number): <T>(list: T[]) => T[];

export function removeIndex(index, list){
  if (arguments.length === 1) return _list => removeIndex(index, _list)
  if (index <= 0) return list.slice(1)
  if (index >= list.length - 1) return list.slice(0, list.length - 1)

  return [ ...list.slice(0, index), ...list.slice(index + 1) ]
}

import { removeIndex } from './removeIndex.js'

const list = [ 1, 2, 3, 4 ]

test('first or before first index', () => {
  expect(removeIndex(-2, list)).toEqual([ 2, 3, 4 ])
  expect(removeIndex(-2)(list)).toEqual([ 2, 3, 4 ])
})

test('last or after last index', () => {
  expect(removeIndex(4, list)).toEqual([ 1, 2, 3 ])
  expect(removeIndex(10, list)).toEqual([ 1, 2, 3 ])
})

test('middle index', () => {
  expect(removeIndex(1, list)).toEqual([ 1, 3, 4 ])
  expect(removeIndex(2, list)).toEqual([ 1, 2, 4 ])
})

import {removeIndex} from 'rambda'

describe('R.removeIndex', () => {
  it('happy', () => {
    const result = removeIndex(1, [1, 2, 3])

    result // $ExpectType number[]
  })
  it('curried', () => {
    const result = removeIndex(1)([1, 2, 3])

    result // $ExpectType number[]
  })
})

repeat


repeat<T>(x: T): (timesToRepeat: number) => T[]

Try this R.repeat example in Rambda REPL

repeat<T>(x: T): (timesToRepeat: number) => T[];
repeat<T>(x: T, timesToRepeat: number): T[];

export function repeat(x, timesToRepeat){
  if (arguments.length === 1){
    return _timesToRepeat => repeat(x, _timesToRepeat)
  }

  return Array(timesToRepeat).fill(x)
}

import { repeat } from './repeat.js'

test('repeat', () => {
  expect(repeat('')(3)).toEqual([ '', '', '' ])
  expect(repeat('foo', 3)).toEqual([ 'foo', 'foo', 'foo' ])

  const obj = {}
  const arr = repeat(obj, 3)

  expect(arr).toEqual([ {}, {}, {} ])

  expect(arr[ 0 ] === arr[ 1 ]).toBeTrue()
})

import {repeat} from 'rambda'

describe('R.repeat', () => {
  it('happy', () => {
    const result = repeat(4, 7)

    result // $ExpectType number[]
  })
  it('curried', () => {
    const result = repeat(4)(7)

    result // $ExpectType number[]
  })
})

replace


replace(strOrRegex: RegExp | string, replacer: RegExpReplacer, str: string): string

It replaces strOrRegex found in str with replacer.

Try this R.replace example in Rambda REPL

replace(strOrRegex: RegExp | string, replacer: RegExpReplacer, str: string): string;
replace(strOrRegex: RegExp | string, replacer: RegExpReplacer): (str: string) => string;
replace(strOrRegex: RegExp | string): (replacer: RegExpReplacer) => (str: string) => string;

import { curry } from './curry.js'

function replaceFn(
  pattern, replacer, str
){
  return str.replace(pattern, replacer)
}

export const replace = curry(replaceFn)

import { replace } from './replace.js'

test('happy', () => {
  expect(replace(
    /\s/g, '|', 'foo bar baz'
  )).toBe('foo|bar|baz')
})

test('with function as replacer input', () => {
  expect(replace(
    /\s/g,
    (
      match, offset, str
    ) => {
      expect(match).toBe(' ')
      expect([ 3, 7 ].includes(offset)).toBeTrue()
      expect(str).toBe('foo bar baz')

      return '|'
    },
    'foo bar baz'
  )).toBe('foo|bar|baz')
})

import {replace} from 'rambda'

const str = 'foo bar foo'
const replacer = 'bar'

describe('R.replace', () => {
  it('happy', () => {
    const result = replace(/foo/g, replacer, str)

    result // $ExpectType string
  })
  it('with string as search pattern', () => {
    const result = replace('foo', replacer, str)

    result // $ExpectType string
  })
  it('with function as replacer', () => {
    const result = replace('f(o)o', (m: string, p1: string, offset: number) => {
      m // $ExpectType string
      p1 // $ExpectType string
      offset // $ExpectType number
      return p1
    }, str)

    result // $ExpectType string
  })
})

describe('R.replace - curried', () => {
  it('happy', () => {
    const result = replace(/foo/g, replacer)(str)

    result // $ExpectType string
  })
  it('with string as search pattern', () => {
    const result = replace('foo', replacer)(str)

    result // $ExpectType string
  })
  it('with function as replacer', () => {
    const result = replace('f(o)o')((m: string, p1: string, offset: number) => {
      m // $ExpectType string
      p1 // $ExpectType string
      offset // $ExpectType number
      return p1
    })(str)

    result // $ExpectType string
  })
})

reverse


reverse<T>(input: T[]): T[]

It returns a reversed copy of list or string input.

Try this R.reverse example in Rambda REPL

reverse<T>(input: T[]): T[];
reverse(input: string): string;

export function reverse(listOrString) {
  if (typeof listOrString === 'string') {
    return listOrString.split('').reverse().join('')
  }

  const clone = listOrString.slice()

  return clone.reverse()
}

import {reverse} from './reverse.js'

test('happy', () => {
  expect(reverse([1, 2, 3])).toEqual([3, 2, 1])
})

test('with string', () => {
  expect(reverse('baz')).toBe('zab')
})

test("it doesn't mutate", () => {
  const arr = [1, 2, 3]

  expect(reverse(arr)).toEqual([3, 2, 1])

  expect(arr).toEqual([1, 2, 3])
})

import {reverse} from 'rambda'

const list = [1, 2, 3, 4, 5]

describe('R.reverse', () => {
  it('happy', () => {
    const result = reverse(list)
    result // $ExpectType number[]
  })
})

set


set<S, A>(lens: Lens<S, A>): {
  (a: A): (obj: S) => S
  (a: A, obj: S): S
}

It returns a copied Object or Array with modified lens focus set to replacer value.

Try this R.set example in Rambda REPL

set<S, A>(lens: Lens<S, A>): {
  (a: A): (obj: S) => S
  (a: A, obj: S): S
};
set<S, A>(lens: Lens<S, A>, a: A): (obj: S) => S;
set<S, A>(lens: Lens<S, A>, a: A, obj: S): S;

import {always} from './always.js'
import {curry} from './curry.js'
import {over} from './over.js'

function setFn(lens, replacer, x) {
  return over(lens, always(replacer), x)
}

export const set = curry(setFn)

import {assoc} from './assoc.js'
import {lens} from './lens.js'
import {lensIndex} from './lensIndex.js'
import {lensPath} from './lensPath.js'
import {prop} from './prop.js'
import {set} from './set.js'

const testObject = {
  foo: 'bar',
  baz: {
    a: 'x',
    b: 'y',
  },
}

test('assoc lens', () => {
  const assocLens = lens(prop('foo'), assoc('foo'))
  const result = set(assocLens, 'FOO', testObject)
  const expected = {
    ...testObject,
    foo: 'FOO',
  }
  expect(result).toEqual(expected)
})

test('path lens', () => {
  const pathLens = lensPath('baz.a')
  const result = set(pathLens, 'z', testObject)
  const expected = {
    ...testObject,
    baz: {
      a: 'z',
      b: 'y',
    },
  }
  expect(result).toEqual(expected)
})

test('index lens', () => {
  const indexLens = lensIndex(0)

  const result = set(indexLens, 3, [1, 2])
  expect(result).toEqual([3, 2])
})

slice


slice(from: number, to: number, input: string): string

Try this R.slice example in Rambda REPL

slice(from: number, to: number, input: string): string;
slice<T>(from: number, to: number, input: T[]): T[];
slice(from: number, to: number): {
  (input: string): string;
  <T>(input: T[]): T[];
};
slice(from: number): {
  (to: number, input: string): string;
  <T>(to: number, input: T[]): T[];
};

import { curry } from './curry.js'

function sliceFn(
  from, to, list
){
  return list.slice(from, to)
}

export const slice = curry(sliceFn)

import { slice } from './slice.js'

test('slice', () => {
  expect(slice(
    1, 3, [ 'a', 'b', 'c', 'd' ]
  )).toEqual([ 'b', 'c' ])
  expect(slice(
    1, Infinity, [ 'a', 'b', 'c', 'd' ]
  )).toEqual([ 'b', 'c', 'd' ])
  expect(slice(
    0, -1, [ 'a', 'b', 'c', 'd' ]
  )).toEqual([ 'a', 'b', 'c' ])
  expect(slice(
    -3, -1, [ 'a', 'b', 'c', 'd' ]
  )).toEqual([ 'b', 'c' ])
  expect(slice(
    0, 3, 'ramda'
  )).toBe('ram')
})

import {slice} from 'rambda'

const list = [1, 2, 3, 4, 5]

describe('R.slice', () => {
  it('happy', () => {
    const result = slice(1, 3, list)
    result // $ExpectType number[]
  })
  it('curried', () => {
    const result = slice(1, 3)(list)
    result // $ExpectType number[]
  })
})

sort


sort<T>(sortFn: (a: T, b: T) => number, list: T[]): T[]

It returns copy of list sorted by sortFn function, where sortFn needs to return only -1, 0 or 1.

Try this R.sort example in Rambda REPL

sort<T>(sortFn: (a: T, b: T) => number, list: T[]): T[];
sort<T>(sortFn: (a: T, b: T) => number): (list: T[]) => T[];

import { cloneList } from './_internals/cloneList.js'

export function sort(sortFn, list){
  if (arguments.length === 1) return _list => sort(sortFn, _list)

  return cloneList(list).sort(sortFn)
}

import { sort } from './sort.js'

const fn = (a, b) => a > b ? 1 : -1

test('sort', () => {
  expect(sort((a, b) => a - b)([ 2, 3, 1 ])).toEqual([ 1, 2, 3 ])
})

test('it doesn\'t mutate', () => {
  const list = [ 'foo', 'bar', 'baz' ]

  expect(sort(fn, list)).toEqual([ 'bar', 'baz', 'foo' ])

  expect(list[ 0 ]).toBe('foo')
  expect(list[ 1 ]).toBe('bar')
  expect(list[ 2 ]).toBe('baz')
})

import {sort} from 'rambda'

const list = [3, 0, 5, 2, 1]

function sortFn(a: number, b: number): number {
  return a > b ? 1 : -1
}

describe('R.sort', () => {
  it('happy', () => {
    const result = sort(sortFn, list)
    result // $ExpectType number[]
  })
  it('curried', () => {
    const result = sort(sortFn)(list)
    result // $ExpectType number[]
  })
})

sortBy


sortBy<T>(sortFn: (a: T) => Ord, list: T[]): T[]

It returns copy of list sorted by sortFn function, where sortFn function returns a value to compare, i.e. it doesn't need to return only -1, 0 or 1.

Try this R.sortBy example in Rambda REPL

sortBy<T>(sortFn: (a: T) => Ord, list: T[]): T[];
sortBy<T>(sortFn: (a: T) => Ord): (list: T[]) => T[];
sortBy(sortFn: (a: any) => Ord): <T>(list: T[]) => T[];

import { cloneList } from './_internals/cloneList.js'

export function sortBy(sortFn, list){
  if (arguments.length === 1) return _list => sortBy(sortFn, _list)

  const clone = cloneList(list)

  return clone.sort((a, b) => {
    const aSortResult = sortFn(a)
    const bSortResult = sortFn(b)

    if (aSortResult === bSortResult) return 0

    return aSortResult < bSortResult ? -1 : 1
  })
}

import { compose } from './compose.js'
import { prop } from './prop.js'
import { sortBy } from './sortBy.js'
import { toLower } from './toLower.js'

test('happy', () => {
  const input = [ { a : 2 }, { a : 1 }, { a : 1 }, { a : 3 } ]
  const expected = [ { a : 1 }, { a : 1 }, { a : 2 }, { a : 3 } ]

  const result = sortBy(x => x.a)(input)
  expect(result).toEqual(expected)
})

test('with compose', () => {
  const alice = {
    name : 'ALICE',
    age  : 101,
  }
  const bob = {
    name : 'Bob',
    age  : -10,
  }
  const clara = {
    name : 'clara',
    age  : 314.159,
  }
  const people = [ clara, bob, alice ]
  const sortByNameCaseInsensitive = sortBy(compose(toLower, prop('name')))

  expect(sortByNameCaseInsensitive(people)).toEqual([ alice, bob, clara ])
})

import {sortBy, pipe} from 'rambda'

interface Input {
  a: number,
}

describe('R.sortBy', () => {
  it('passing type to sort function', () => {
    function fn(x: any): number {
      return x.a
    }
    function fn2(x: Input): number {
      return x.a
    }

    const input = [{a: 2}, {a: 1}, {a: 0}]
    const result = sortBy(fn, input)
    const curriedResult = sortBy(fn2)(input)

    result // $ExpectType { a: number; }[]
    curriedResult // $ExpectType Input[]
    result[0].a // $ExpectType number
    curriedResult[0].a // $ExpectType number
  })
  it('passing type to sort function and list', () => {
    function fn(x: Input): number {
      return x.a
    }

    const input: Input[] = [{a: 2}, {a: 1}, {a: 0}]
    const result = sortBy(fn, input)
    const curriedResult = sortBy(fn)(input)

    result // $ExpectType Input[]
    curriedResult // $ExpectType Input[]
    result[0].a // $ExpectType number
  })
  it('with R.pipe', () => {
    interface Obj {
      value: number,
    }
    const fn = pipe(sortBy<Obj>(x => x.value))

    const result = fn([{value: 1}, {value: 2}])
    result // $ExpectType Obj[]
  })
})

sortWith

Try this R.sortWith example in Rambda REPL

split


split(separator: string | RegExp): (str: string) => string[]

Curried version of String.prototype.split

Try this R.split example in Rambda REPL

split(separator: string | RegExp): (str: string) => string[];
split(separator: string | RegExp, str: string): string[];

export function split(separator, str){
  if (arguments.length === 1) return _str => split(separator, _str)

  return str.split(separator)
}

import { split } from './split.js'

const str = 'foo|bar|baz'
const splitChar = '|'
const expected = [ 'foo', 'bar', 'baz' ]

test('happy', () => {
  expect(split(splitChar, str)).toEqual(expected)
})

test('curried', () => {
  expect(split(splitChar)(str)).toEqual(expected)
})

import {split} from 'rambda'

const str = 'foo|bar|baz'
const splitChar = '|'

describe('R.split', () => {
  it('happy', () => {
    const result = split(splitChar, str)

    result // $ExpectType string[]
  })
  it('curried', () => {
    const result = split(splitChar)(str)

    result // $ExpectType string[]
  })
})

splitAt


splitAt<T>(index: number, input: T[]): [T[], T[]]

It splits string or array at a given index.

Try this R.splitAt example in Rambda REPL

splitAt<T>(index: number, input: T[]): [T[], T[]];
splitAt(index: number, input: string): [string, string];
splitAt(index: number): {
    <T>(input: T[]): [T[], T[]];
    (input: string): [string, string];
};

import { isArray } from './_internals/isArray.js'
import { drop } from './drop.js'
import { maybe } from './maybe.js'
import { take } from './take.js'

export function splitAt(index, input){
  if (arguments.length === 1){
    return _list => splitAt(index, _list)
  }
  if (!input) throw new TypeError(`Cannot read property 'slice' of ${ input }`)

  if (!isArray(input) && typeof input !== 'string') return [ [], [] ]

  const correctIndex = maybe(
    index < 0,
    input.length + index < 0 ? 0 : input.length + index,
    index
  )

  return [ take(correctIndex, input), drop(correctIndex, input) ]
}

import { splitAt as splitAtRamda } from 'ramda'

import { splitAt } from './splitAt.js'

const list = [ 1, 2, 3 ]
const str = 'foo bar'

test('with array', () => {
  const result = splitAt(2, list)
  expect(result).toEqual([ [ 1, 2 ], [ 3 ] ])
})

test('with array - index is negative number', () => {
  const result = splitAt(-6, list)
  expect(result).toEqual([ [], list ])
})

test('with array - index is out of scope', () => {
  const result = splitAt(4, list)
  expect(result).toEqual([ [ 1, 2, 3 ], [] ])
})

test('with string', () => {
  const result = splitAt(4, str)
  expect(result).toEqual([ 'foo ', 'bar' ])
})

test('with string - index is negative number', () => {
  const result = splitAt(-2, str)
  expect(result).toEqual([ 'foo b', 'ar' ])
})

test('with string - index is out of scope', () => {
  const result = splitAt(10, str)
  expect(result).toEqual([ str, '' ])
})

test('with array - index is out of scope', () => {
  const result = splitAt(4)(list)
  expect(result).toEqual([ [ 1, 2, 3 ], [] ])
})

const badInputs = [ 1, true, /foo/g, {} ]
const throwingBadInputs = [ null, undefined ]

test('with bad inputs', () => {
  throwingBadInputs.forEach(badInput => {
    expect(() => splitAt(1, badInput)).toThrowWithMessage(TypeError,
      `Cannot read property 'slice' of ${ badInput }`)
    expect(() => splitAtRamda(1, badInput)).toThrowWithMessage(TypeError,
      `Cannot read properties of ${ badInput } (reading 'slice')`)
  })

  badInputs.forEach(badInput => {
    const result = splitAt(1, badInput)
    const ramdaResult = splitAtRamda(1, badInput)
    expect(result).toEqual(ramdaResult)
  })
})

import {splitAt} from 'rambda'

const index = 1
const str = 'foo'
const list = [1, 2, 3]

describe('R.splitAt with array', () => {
  it('happy', () => {
    const result = splitAt(index, list)

    result // $ExpectType [number[], number[]]
  })
  it('curried', () => {
    const result = splitAt(index)(list)

    result // $ExpectType [number[], number[]]
  })
})

describe('R.splitAt with string', () => {
  it('happy', () => {
    const result = splitAt(index, str)

    result // $ExpectType [string, string]
  })
  it('curried', () => {
    const result = splitAt(index)(str)

    result // $ExpectType [string, string]
  })
})

splitEvery


splitEvery<T>(sliceLength: number, input: T[]): (T[])[]

It splits input into slices of sliceLength.

Try this R.splitEvery example in Rambda REPL

splitEvery<T>(sliceLength: number, input: T[]): (T[])[];
splitEvery(sliceLength: number, input: string): string[];
splitEvery(sliceLength: number): {
  (input: string): string[];
  <T>(input: T[]): (T[])[];
};

export function splitEvery(sliceLength, listOrString){
  if (arguments.length === 1){
    return _listOrString => splitEvery(sliceLength, _listOrString)
  }

  if (sliceLength < 1){
    throw new Error('First argument to splitEvery must be a positive integer')
  }

  const willReturn = []
  let counter = 0

  while (counter < listOrString.length){
    willReturn.push(listOrString.slice(counter, counter += sliceLength))
  }

  return willReturn
}

import { splitEvery } from './splitEvery.js'

test('happy', () => {
  expect(splitEvery(3, [ 1, 2, 3, 4, 5, 6, 7 ])).toEqual([
    [ 1, 2, 3 ],
    [ 4, 5, 6 ],
    [ 7 ],
  ])

  expect(splitEvery(3)('foobarbaz')).toEqual([ 'foo', 'bar', 'baz' ])
})

test('with bad input', () => {
  expect(() =>
    expect(splitEvery(0)('foo')).toEqual([ 'f', 'o', 'o' ])).toThrowErrorMatchingInlineSnapshot('"First argument to splitEvery must be a positive integer"')
})

import {splitEvery} from 'rambda'

const list = [1, 2, 3, 4, 5, 6, 7]

describe('R.splitEvery', () => {
  it('happy', () => {
    const result = splitEvery(3, list)

    result // $ExpectType number[][]
  })
  it('curried', () => {
    const result = splitEvery(3)(list)

    result // $ExpectType number[][]
  })
})

splitWhen


splitWhen<T, U>(predicate: Predicate<T>, list: U[]): (U[])[]

It splits list to two arrays according to a predicate function.

The first array contains all members of list before predicate returns true.

Try this R.splitWhen example in Rambda REPL

splitWhen<T, U>(predicate: Predicate<T>, list: U[]): (U[])[];
splitWhen<T>(predicate: Predicate<T>): <U>(list: U[]) => (U[])[];

export function splitWhen(predicate, input){
  if (arguments.length === 1){
    return _input => splitWhen(predicate, _input)
  }
  if (!input)
    throw new TypeError(`Cannot read property 'length' of ${ input }`)

  const preFound = []
  const postFound = []
  let found = false
  let counter = -1

  while (counter++ < input.length - 1){
    if (found){
      postFound.push(input[ counter ])
    } else if (predicate(input[ counter ])){
      postFound.push(input[ counter ])
      found = true
    } else {
      preFound.push(input[ counter ])
    }
  }

  return [ preFound, postFound ]
}

import { splitWhen as splitWhenRamda } from 'ramda'

import { equals } from './equals.js'
import { splitWhen } from './splitWhen.js'

const list = [ 1, 2, 1, 2 ]

test('happy', () => {
  const result = splitWhen(equals(2), list)
  expect(result).toEqual([ [ 1 ], [ 2, 1, 2 ] ])
})

test('when predicate returns false', () => {
  const result = splitWhen(equals(3))(list)
  expect(result).toEqual([ list, [] ])
})

const badInputs = [ 1, true, /foo/g, {} ]
const throwingBadInputs = [ null, undefined ]

test('with bad inputs', () => {
  throwingBadInputs.forEach(badInput => {
    expect(() => splitWhen(equals(2), badInput)).toThrowWithMessage(TypeError,
      `Cannot read property 'length' of ${ badInput }`)
    expect(() => splitWhenRamda(equals(2), badInput)).toThrowWithMessage(TypeError,
      `Cannot read properties of ${ badInput } (reading 'length')`)
  })

  badInputs.forEach(badInput => {
    const result = splitWhen(equals(2), badInput)
    const ramdaResult = splitWhenRamda(equals(2), badInput)
    expect(result).toEqual(ramdaResult)
  })
})

import {splitWhen} from 'rambda'

const list = [1, 2, 1, 2]
const predicate = (x: number) => x === 2

describe('R.splitWhen', () => {
  it('happy', () => {
    const result = splitWhen(predicate, list)

    result // $ExpectType number[][]
  })
  it('curried', () => {
    const result = splitWhen(predicate)(list)

    result // $ExpectType number[][]
  })
})

startsWith


startsWith<T extends string>(question: T, input: string): boolean

When iterable is a string, then it behaves as String.prototype.startsWith. When iterable is a list, then it uses R.equals to determine if the target list starts in the same way as the given target.

Try this R.startsWith example in Rambda REPL

startsWith<T extends string>(question: T, input: string): boolean;
startsWith<T extends string>(question: T): (input: string) => boolean;
startsWith<T>(question: T[], input: T[]): boolean;
startsWith<T>(question: T[]): (input: T[]) => boolean;

import { isArray } from './_internals/isArray.js'
import { equals } from './equals.js'

export function startsWith(question, iterable){
  if (arguments.length === 1)
    return _iterable => startsWith(question, _iterable)

  if (typeof iterable === 'string'){
    return iterable.startsWith(question)
  }
  if (!isArray(question)) return false

  let correct = true
  const filtered = question.filter((x, index) => {
    if (!correct) return false
    const result = equals(x, iterable[ index ])
    if (!result) correct = false

    return result
  })

  return filtered.length === question.length
}

import { startsWith as startsWithRamda } from 'ramda'

import { compareCombinations } from './_internals/testUtils.js'
import { possibleIterables, possibleTargets } from './endsWith.spec.js'
import { startsWith } from './startsWith.js'

test('with string', () => {
  expect(startsWith('foo', 'foo-bar')).toBeTrue()
  expect(startsWith('baz')('foo-bar')).toBeFalse()
})

test('use R.equals with array', () => {
  const list = [ { a : 1 }, { a : 2 }, { a : 3 } ]
  expect(startsWith({ a : 1 }, list)).toBeFalse()
  expect(startsWith([ { a : 1 } ], list)).toBeTrue()
  expect(startsWith([ { a : 1 }, { a : 2 } ], list)).toBeTrue()
  expect(startsWith(list, list)).toBeTrue()
  expect(startsWith([ { a : 2 } ], list)).toBeFalse()
})

describe('brute force', () => {
  compareCombinations({
    fn          : startsWith,
    fnRamda     : startsWithRamda,
    firstInput  : possibleTargets,
    secondInput : possibleIterables,
    callback    : errorsCounters => {
      expect(errorsCounters).toMatchInlineSnapshot(`
        {
          "ERRORS_MESSAGE_MISMATCH": 0,
          "ERRORS_TYPE_MISMATCH": 0,
          "RESULTS_MISMATCH": 0,
          "SHOULD_NOT_THROW": 0,
          "SHOULD_THROW": 0,
          "TOTAL_TESTS": 32,
        }
      `)
    },
  })
})

import {startsWith} from 'rambda'

describe('R.startsWith - array', () => {
  const question = [{a: 1}]
  const iterable = [{a: 1}, {a: 2}]
  it('happy', () => {
    const result = startsWith(question, iterable)
    result // $ExpectType boolean
  })
  it('curried', () => {
    const result = startsWith(question)(iterable)
    result // $ExpectType boolean
  })
})

describe('R.startsWith - string', () => {
  const question = 'foo'
  const iterable = 'foo bar'
  it('happy', () => {
    const result = startsWith(question, iterable)
    result // $ExpectType boolean
  })
  it('curried', () => {
    const result = startsWith(question)(iterable)
    result // $ExpectType boolean
  })
})

subtract

Curried version of x - y

Try this R.subtract example in Rambda REPL

sum


sum(list: number[]): number

Try this R.sum example in Rambda REPL

sum(list: number[]): number;

export function sum(list){
  return list.reduce((prev, current) => prev + current, 0)
}

import { sum } from './sum.js'

test('happy', () => {
  expect(sum([ 1, 2, 3, 4, 5 ])).toBe(15)
})

swap

Try this R.swap example in Rambda REPL

symmetricDifference


symmetricDifference<T>(x: T[], y: T[]): T[]

It returns a merged list of x and y with all equal elements removed.

R.equals is used to determine equality.

Try this R.symmetricDifference example in Rambda REPL

symmetricDifference<T>(x: T[], y: T[]): T[];
symmetricDifference<T>(x: T[]): <T>(y: T[]) => T[];

import { concat } from './concat.js'
import { filter } from './filter.js'
import { includes } from './includes.js'

export function symmetricDifference(x, y){
  if (arguments.length === 1){
    return _y => symmetricDifference(x, _y)
  }

  return concat(filter(value => !includes(value, y), x),
    filter(value => !includes(value, x), y))
}

import { symmetricDifference } from './symmetricDifference.js'

test('symmetricDifference', () => {
  const list1 = [ 1, 2, 3, 4 ]
  const list2 = [ 3, 4, 5, 6 ]
  expect(symmetricDifference(list1)(list2)).toEqual([ 1, 2, 5, 6 ])

  expect(symmetricDifference([], [])).toEqual([])
})

test('symmetricDifference with objects', () => {
  const list1 = [ { id : 1 }, { id : 2 }, { id : 3 }, { id : 4 } ]
  const list2 = [ { id : 3 }, { id : 4 }, { id : 5 }, { id : 6 } ]
  expect(symmetricDifference(list1)(list2)).toEqual([
    { id : 1 },
    { id : 2 },
    { id : 5 },
    { id : 6 },
  ])
})

import {symmetricDifference} from 'rambda'

describe('R.symmetricDifference', () => {
  it('happy', () => {
    const list1 = [1, 2, 3, 4]
    const list2 = [3, 4, 5, 6]
    const result = symmetricDifference(list1, list2)

    result // $ExpectType number[]
  })

  it('curried', () => {
    const list1 = [{id: 1}, {id: 2}, {id: 3}, {id: 4}]
    const list2 = [{id: 3}, {id: 4}, {id: 5}, {id: 6}]
    const result = symmetricDifference(list1)(list2)

    result // $ExpectType { id: number; }[]
  })
})

T


T(): boolean

Try this R.T example in Rambda REPL

T(): boolean;

export function T(){
  return true
}

tail


tail<T extends unknown[]>(input: T): T extends [any, ...infer U] ? U : [...T]

It returns all but the first element of input.

Try this R.tail example in Rambda REPL

tail<T extends unknown[]>(input: T): T extends [any, ...infer U] ? U : [...T];
tail(input: string): string;

import { drop } from './drop.js'

export function tail(listOrString){
  return drop(1, listOrString)
}

import { tail } from './tail.js'

test('tail', () => {
  expect(tail([ 1, 2, 3 ])).toEqual([ 2, 3 ])
  expect(tail([ 1, 2 ])).toEqual([ 2 ])
  expect(tail([ 1 ])).toEqual([])
  expect(tail([])).toEqual([])

  expect(tail('abc')).toBe('bc')
  expect(tail('ab')).toBe('b')
  expect(tail('a')).toBe('')
  expect(tail('')).toBe('')
})

import {tail} from 'rambda'

describe('R.tail', () => {
  it('with string', () => {
    const result = tail('foo')

    result // $ExpectType string
  })
  it('with list - one type', () => {
    const result = tail([1, 2, 3])

    result // $ExpectType number[]
  })
  it('with list - mixed types', () => {
    const result = tail(['foo', 'bar', 1, 2, 3])

    result // $ExpectType (string | number)[]
  })
})

take


take<T>(howMany: number, input: T[]): T[]

It returns the first howMany elements of input.

Try this R.take example in Rambda REPL

take<T>(howMany: number, input: T[]): T[];
take(howMany: number, input: string): string;
take<T>(howMany: number): {
  <T>(input: T[]): T[];
  (input: string): string;
};

import baseSlice from './_internals/baseSlice.js'

export function take(howMany, listOrString){
  if (arguments.length === 1)
    return _listOrString => take(howMany, _listOrString)
  if (howMany < 0) return listOrString.slice()
  if (typeof listOrString === 'string') return listOrString.slice(0, howMany)

  return baseSlice(
    listOrString, 0, howMany
  )
}

import { take } from './take.js'

test('happy', () => {
  const arr = [ 'foo', 'bar', 'baz' ]

  expect(take(1, arr)).toEqual([ 'foo' ])

  expect(arr).toEqual([ 'foo', 'bar', 'baz' ])

  expect(take(2)([ 'foo', 'bar', 'baz' ])).toEqual([ 'foo', 'bar' ])
  expect(take(3, [ 'foo', 'bar', 'baz' ])).toEqual([ 'foo', 'bar', 'baz' ])
  expect(take(4, [ 'foo', 'bar', 'baz' ])).toEqual([ 'foo', 'bar', 'baz' ])
  expect(take(3)('rambda')).toBe('ram')
})

test('with negative index', () => {
  expect(take(-1, [ 1, 2, 3 ])).toEqual([ 1, 2, 3 ])
  expect(take(-Infinity, [ 1, 2, 3 ])).toEqual([ 1, 2, 3 ])
})

test('with zero index', () => {
  expect(take(0, [ 1, 2, 3 ])).toEqual([])
})

import {take} from 'rambda'

const list = [1, 2, 3, 4]
const str = 'foobar'
const howMany = 2

describe('R.take - array', () => {
  it('happy', () => {
    const result = take(howMany, list)

    result // $ExpectType number[]
  })
  it('curried', () => {
    const result = take(howMany)(list)

    result // $ExpectType number[]
  })
})

describe('R.take - string', () => {
  it('happy', () => {
    const result = take(howMany, str)

    result // $ExpectType string
  })
  it('curried', () => {
    const result = take(howMany)(str)

    result // $ExpectType string
  })
})

takeLast


takeLast<T>(howMany: number, input: T[]): T[]

It returns the last howMany elements of input.

Try this R.takeLast example in Rambda REPL

takeLast<T>(howMany: number, input: T[]): T[];
takeLast(howMany: number, input: string): string;
takeLast<T>(howMany: number): {
  <T>(input: T[]): T[];
  (input: string): string;
};

import baseSlice from './_internals/baseSlice.js'

export function takeLast(howMany, listOrString){
  if (arguments.length === 1)
    return _listOrString => takeLast(howMany, _listOrString)

  const len = listOrString.length
  if (howMany < 0) return listOrString.slice()
  let numValue = howMany > len ? len : howMany

  if (typeof listOrString === 'string')
    return listOrString.slice(len - numValue)

  numValue = len - numValue

  return baseSlice(
    listOrString, numValue, len
  )
}

import { takeLast } from './takeLast.js'

test('with arrays', () => {
  expect(takeLast(1, [ 'foo', 'bar', 'baz' ])).toEqual([ 'baz' ])

  expect(takeLast(2)([ 'foo', 'bar', 'baz' ])).toEqual([ 'bar', 'baz' ])

  expect(takeLast(3, [ 'foo', 'bar', 'baz' ])).toEqual([ 'foo', 'bar', 'baz' ])

  expect(takeLast(4, [ 'foo', 'bar', 'baz' ])).toEqual([ 'foo', 'bar', 'baz' ])

  expect(takeLast(10, [ 'foo', 'bar', 'baz' ])).toEqual([ 'foo', 'bar', 'baz' ])
})

test('with strings', () => {
  expect(takeLast(3, 'rambda')).toBe('bda')

  expect(takeLast(7, 'rambda')).toBe('rambda')
})

test('with negative index', () => {
  expect(takeLast(-1, [ 1, 2, 3 ])).toEqual([ 1, 2, 3 ])
  expect(takeLast(-Infinity, [ 1, 2, 3 ])).toEqual([ 1, 2, 3 ])
})

import {takeLast} from 'rambda'

const list = [1, 2, 3, 4]
const str = 'foobar'
const howMany = 2

describe('R.takeLast - array', () => {
  it('happy', () => {
    const result = takeLast(howMany, list)

    result // $ExpectType number[]
  })
  it('curried', () => {
    const result = takeLast(howMany)(list)

    result // $ExpectType number[]
  })
})

describe('R.takeLast - string', () => {
  it('happy', () => {
    const result = takeLast(howMany, str)

    result // $ExpectType string
  })
  it('curried', () => {
    const result = takeLast(howMany)(str)

    result // $ExpectType string
  })
})

takeLastWhile


takeLastWhile(predicate: (x: string) => boolean, input: string): string

Try this R.takeLastWhile example in Rambda REPL

takeLastWhile(predicate: (x: string) => boolean, input: string): string;
takeLastWhile(predicate: (x: string) => boolean): (input: string) => string;
takeLastWhile<T>(predicate: (x: T) => boolean, input: T[]): T[];
takeLastWhile<T>(predicate: (x: T) => boolean): <T>(input: T[]) => T[];

import { isArray } from './_internals/isArray.js'

export function takeLastWhile(predicate, input){
  if (arguments.length === 1){
    return _input => takeLastWhile(predicate, _input)
  }
  if (input.length === 0) return input

  const toReturn = []
  let counter = input.length

  while (counter){
    const item = input[ --counter ]
    if (!predicate(item)){
      break
    }
    toReturn.push(item)
  }

  return isArray(input) ? toReturn.reverse() : toReturn.reverse().join('')
}

import { takeLastWhile } from './takeLastWhile.js'
const assert = require('assert')

const list = [ 1, 2, 3, 4 ]

test('happy', () => {
  const predicate = x => x > 2
  const result = takeLastWhile(predicate, list)
  expect(result).toEqual([ 3, 4 ])
})

test('predicate is always true', () => {
  const predicate = () => true
  const result = takeLastWhile(predicate)(list)
  expect(result).toEqual(list)
})

test('predicate is always false', () => {
  const predicate = () => false
  const result = takeLastWhile(predicate, list)
  expect(result).toEqual([])
})

test('with string', () => {
  const result = takeLastWhile(x => x !== 'F', 'FOOBAR')
  expect(result).toBe('OOBAR')
})

import {takeLastWhile} from 'rambda'

const list = [1, 2, 3]
const str = 'FOO'

describe('R.takeLastWhile', () => {
  it('with array', () => {
    const result = takeLastWhile(x => x > 1, list)

    result // $ExpectType number[]
  })
  it('with array - curried', () => {
    const result = takeLastWhile(x => x > 1, list)

    result // $ExpectType number[]
  })
  it('with string', () => {
    const result = takeLastWhile(x => x !== 'F', str)

    result // $ExpectType string
  })
  it('with string - curried', () => {
    const result = takeLastWhile(x => x !== 'F')(str)

    result // $ExpectType string
  })
})

takeWhile

Try this R.takeWhile example in Rambda REPL

tap


tap<T>(fn: (x: T) => void, input: T): T

It applies function fn to input x and returns x.

One use case is debugging in the middle of R.compose.

Try this R.tap example in Rambda REPL

tap<T>(fn: (x: T) => void, input: T): T;
tap<T>(fn: (x: T) => void): (input: T) => T;

export function tap(fn, x){
  if (arguments.length === 1) return _x => tap(fn, _x)

  fn(x)

  return x
}

import { tap } from './tap.js'

test('tap', () => {
  let a = 1
  const sayX = x => a = x

  expect(tap(sayX, 100)).toBe(100)
  expect(tap(sayX)(100)).toBe(100)
  expect(a).toBe(100)
})

import {tap, pipe} from 'rambda'

describe('R.tap', () => {
  it('happy', () => {
    pipe(
      tap(x => {
        x // $ExpectType number[]
      }),
      (x: number[]) => x.length
    )([1, 2])
  })
})

test


test(regExpression: RegExp): (str: string) => boolean

It determines whether str matches regExpression.

Try this R.test example in Rambda REPL

test(regExpression: RegExp): (str: string) => boolean;
test(regExpression: RegExp, str: string): boolean;

export function test(pattern, str){
  if (arguments.length === 1) return _str => test(pattern, _str)

  if (typeof pattern === 'string'){
    throw new TypeError(`R.test requires a value of type RegExp as its first argument; received "${ pattern }"`)
  }

  return str.search(pattern) !== -1
}

import { test as testMethod } from './test.js'

test('happy', () => {
  expect(testMethod(/^x/, 'xyz')).toBeTrue()

  expect(testMethod(/^y/)('xyz')).toBeFalse()
})

test('throws if first argument is not regex', () => {
  expect(() => testMethod('foo', 'bar')).toThrowErrorMatchingInlineSnapshot('"R.test requires a value of type RegExp as its first argument; received "foo""')
})

import {test} from 'rambda'

const input = 'foo   '
const regex = /foo/

describe('R.test', () => {
  it('happy', () => {
    const result = test(regex, input)

    result // $ExpectType boolean
  })
  it('curried', () => {
    const result = test(regex)(input)

    result // $ExpectType boolean
  })
})

times


times<T>(fn: (i: number) => T, howMany: number): T[]

It returns the result of applying function fn over members of range array.

The range array includes numbers between 0 and howMany(exclusive).

Try this R.times example in Rambda REPL

times<T>(fn: (i: number) => T, howMany: number): T[];
times<T>(fn: (i: number) => T): (howMany: number) => T[];

import { isInteger } from './_internals/isInteger.js'
import { map } from './map.js'
import { range } from './range.js'

export function times(fn, howMany){
  if (arguments.length === 1) return _howMany => times(fn, _howMany)
  if (!isInteger(howMany) || howMany < 0){
    throw new RangeError('n must be an integer')
  }

  return map(fn, range(0, howMany))
}

import assert from 'assert'

import { identity } from './identity.js'
import { times } from './times.js'

test('happy', () => {
  const result = times(identity, 5)

  expect(result).toEqual([ 0, 1, 2, 3, 4 ])
})

test('with bad input', () => {
  assert.throws(() => {
    times(3)('cheers!')
  }, RangeError)
  assert.throws(() => {
    times(identity, -1)
  }, RangeError)
})

test('curry', () => {
  const result = times(identity)(5)

  expect(result).toEqual([ 0, 1, 2, 3, 4 ])
})

import {times, identity} from 'rambda'

describe('R.times', () => {
  it('happy', () => {
    const result = times(identity, 5)
    result // $ExpectType number[]
  })
})

toLower


toLower<S extends string>(str: S): Lowercase<S>

Try this R.toLower example in Rambda REPL

toLower<S extends string>(str: S): Lowercase<S>;
toLower(str: string): string;

export function toLower(str){
  return str.toLowerCase()
}

import { toLower } from './toLower.js'

test('toLower', () => {
  expect(toLower('FOO|BAR|BAZ')).toBe('foo|bar|baz')
})

toPairs


toPairs<O extends object, K extends Extract<keyof O, string | number>>(obj: O): Array<{ [key in K]: [`${key}`, O[key]] }[K]>

It transforms an object to a list.

Try this R.toPairs example in Rambda REPL

toPairs<O extends object, K extends Extract<keyof O, string | number>>(obj: O): Array<{ [key in K]: [`${key}`, O[key]] }[K]>;
toPairs<S>(obj: Record<string | number, S>): Array<[string, S]>;

export function toPairs(obj){
  return Object.entries(obj)
}

import { toPairs } from './toPairs.js'

const obj = {
  a : 1,
  b : 2,
  c : [ 3, 4 ],
}
const expected = [
  [ 'a', 1 ],
  [ 'b', 2 ],
  [ 'c', [ 3, 4 ] ],
]

test('happy', () => {
  expect(toPairs(obj)).toEqual(expected)
})

toString


toString(x: unknown): string

Try this R.toString example in Rambda REPL

toString(x: unknown): string;

export function toString(x){
  return x.toString()
}

import { toString } from './toString.js'

test('happy', () => {
  expect(toString([ 1, 2, 3 ])).toBe('1,2,3')
})

toUpper


toUpper<S extends string>(str: S): Uppercase<S>

Try this R.toUpper example in Rambda REPL

toUpper<S extends string>(str: S): Uppercase<S>;
toUpper(str: string): string;

export function toUpper(str){
  return str.toUpperCase()
}

import { toUpper } from './toUpper.js'

test('toUpper', () => {
  expect(toUpper('foo|bar|baz')).toBe('FOO|BAR|BAZ')
})

transpose


transpose<T>(list: (T[])[]): (T[])[]

Try this R.transpose example in Rambda REPL

transpose<T>(list: (T[])[]): (T[])[];

import { isArray } from './_internals/isArray.js'

export function transpose(array){
  return array.reduce((acc, el) => {
    el.forEach((nestedEl, i) =>
      isArray(acc[ i ]) ? acc[ i ].push(nestedEl) : acc.push([ nestedEl ]))

    return acc
  }, [])
}

import { transpose } from './transpose.js'

test('happy', () => {
  const input = [
    [ 'a', 1 ],
    [ 'b', 2 ],
    [ 'c', 3 ],
  ]

  expect(transpose(input)).toEqual([
    [ 'a', 'b', 'c' ],
    [ 1, 2, 3 ],
  ])
})

test('when rows are shorter', () => {
  const actual = transpose([ [ 10, 11 ], [ 20 ], [], [ 30, 31, 32 ] ])
  const expected = [ [ 10, 20, 30 ], [ 11, 31 ], [ 32 ] ]
  expect(actual).toEqual(expected)
})

test('with empty array', () => {
  expect(transpose([])).toEqual([])
})

test('array with falsy values', () => {
  const actual = transpose([
    [ true, false, undefined, null ],
    [ null, undefined, false, true ],
  ])
  const expected = [
    [ true, null ],
    [ false, undefined ],
    [ undefined, false ],
    [ null, true ],
  ]
  expect(actual).toEqual(expected)
})

import {transpose} from 'rambda'

const input = [
  ['a', 1],
  ['b', 2],
  ['c', 3],
]

describe('R.transpose', () => {
  it('happy', () => {
    const result = transpose(input)

    result // $ExpectType (string | number)[][]
  })
})

trim


trim(str: string): string

Try this R.trim example in Rambda REPL

trim(str: string): string;

export function trim(str){
  return str.trim()
}

import { trim } from './trim.js'

test('trim', () => {
  expect(trim(' foo ')).toBe('foo')
})

tryCatch

It returns function that runs fn in try/catch block. If there was an error, then fallback is used to return the result. Note that fn can be value or asynchronous/synchronous function(unlike Ramda where fallback can only be a synchronous function).

Try this R.tryCatch example in Rambda REPL

type

It accepts any input and it returns its type.

Try this R.type example in Rambda REPL

unapply


unapply<T = any>(fn: (args: any[]) => T): (...args: any[]) => T

It calls a function fn with the list of values of the returned function.

R.unapply is the opposite of R.apply method.

Try this R.unapply example in Rambda REPL

unapply<T = any>(fn: (args: any[]) => T): (...args: any[]) => T;

export function unapply(fn){
  return function (...args){
    return fn.call(this, args)
  }
}

import { apply } from './apply.js'
import { converge } from './converge.js'
import { identity } from './identity.js'
import { prop } from './prop.js'
import { sum } from './sum.js'
import { unapply } from './unapply.js'

test('happy', () => {
  const fn = unapply(identity)
  expect(fn(
    1, 2, 3
  )).toEqual([ 1, 2, 3 ])
  expect(fn()).toEqual([])
})

test('returns a function which is always passed one argument', () => {
  const fn = unapply(function (){
    return arguments.length
  })
  expect(fn('x')).toBe(1)
  expect(fn('x', 'y')).toBe(1)
  expect(fn(
    'x', 'y', 'z'
  )).toBe(1)
})

test('forwards arguments to decorated function as an array', () => {
  const fn = unapply(xs => '[' + xs + ']')
  expect(fn(2)).toBe('[2]')
  expect(fn(2, 4)).toBe('[2,4]')
  expect(fn(
    2, 4, 6
  )).toBe('[2,4,6]')
})

test('returns a function with length 0', () => {
  const fn = unapply(identity)
  expect(fn).toHaveLength(0)
})

test('is the inverse of R.apply', () => {
  let a, b, c, d, e, f, g, n
  const rand = function (){
    return Math.floor(200 * Math.random()) - 100
  }

  f = Math.max
  g = unapply(apply(f))
  n = 1
  while (n <= 100){
    a = rand()
    b = rand()
    c = rand()
    d = rand()
    e = rand()
    expect(f(
      a, b, c, d, e
    )).toEqual(g(
      a, b, c, d, e
    ))
    n += 1
  }

  f = function (xs){
    return '[' + xs + ']'
  }
  g = apply(unapply(f))
  n = 1
  while (n <= 100){
    a = rand()
    b = rand()
    c = rand()
    d = rand()
    e = rand()
    expect(f([ a, b, c, d, e ])).toEqual(g([ a, b, c, d, e ]))
    n += 1
  }
})

test('it works with converge', () => {
  const fn = unapply(sum)
  const convergeFn = converge(fn, [ prop('a'), prop('b'), prop('c') ])
  const obj = {
    a : 1337,
    b : 42,
    c : 1,
  }
  const expected = 1337 + 42 + 1
  expect(convergeFn(obj)).toEqual(expected)
})

import {join, unapply, sum} from 'rambda'

describe('R.unapply', () => {
  it('happy', () => {
    const fn = unapply(sum)

    fn(1, 2, 3) // $ExpectType number
  })

  it('joins a string', () => {
    const fn = unapply(join(''))

    fn('s', 't', 'r', 'i', 'n', 'g') // $ExpectType string
  })
})

union


union<T>(x: T[], y: T[]): T[]

It takes two lists and return a new list containing a merger of both list with removed duplicates.

R.equals is used to compare for duplication.

Try this R.union example in Rambda REPL

union<T>(x: T[], y: T[]): T[];
union<T>(x: T[]): (y: T[]) => T[];

import { cloneList } from './_internals/cloneList.js'
import { includes } from './includes.js'

export function union(x, y){
  if (arguments.length === 1) return _y => union(x, _y)

  const toReturn = cloneList(x)

  y.forEach(yInstance => {
    if (!includes(yInstance, x)) toReturn.push(yInstance)
  })

  return toReturn
}

import { union } from './union.js'

test('happy', () => {
  expect(union([ 1, 2 ], [ 2, 3 ])).toEqual([ 1, 2, 3 ])
})

test('with list of objects', () => {
  const list1 = [ { a : 1 }, { a : 2 } ]
  const list2 = [ { a : 2 }, { a : 3 } ]
  const result = union(list1)(list2)
})

import {union} from 'rambda'

describe('R.union', () => {
  it('happy', () => {
    const result = union([1, 2], [2, 3])

    result // $ExpectType number[]
  })
  it('with array of objects - case 1', () => {
    const list1 = [{a: 1}, {a: 2}]
    const list2 = [{a: 2}, {a: 3}]
    const result = union(list1, list2)
    result // $ExpectType { a: number; }[]
  })
  it('with array of objects - case 2', () => {
    const list1 = [{a: 1, b: 1}, {a: 2}]
    const list2 = [{a: 2}, {a: 3, b: 3}]
    const result = union(list1, list2)
    result[0].a // $ExpectType number
    result[0].b // $ExpectType number | undefined
  })
})

describe('R.union - curried', () => {
  it('happy', () => {
    const result = union([1, 2])([2, 3])

    result // $ExpectType number[]
  })
  it('with array of objects - case 1', () => {
    const list1 = [{a: 1}, {a: 2}]
    const list2 = [{a: 2}, {a: 3}]
    const result = union(list1)(list2)
    result // $ExpectType { a: number; }[]
  })
  it('with array of objects - case 2', () => {
    const list1 = [{a: 1, b: 1}, {a: 2}]
    const list2 = [{a: 2}, {a: 3, b: 3}]
    const result = union(list1)(list2)
    result[0].a // $ExpectType number
    result[0].b // $ExpectType number | undefined
  })
})

uniq


uniq<T>(list: T[]): T[]

It returns a new array containing only one copy of each element of list.

R.equals is used to determine equality.

Try this R.uniq example in Rambda REPL

uniq<T>(list: T[]): T[];

import { _Set } from './_internals/set.js'

export function uniq(list){
  const set = new _Set()
  const willReturn = []
  list.forEach(item => {
    if (set.checkUniqueness(item)){
      willReturn.push(item)
    }
  })

  return willReturn
}

import { uniq } from './uniq.js'

test('happy', () => {
  const list = [ 1, 2, 3, 3, 3, 1, 2, 0 ]
  expect(uniq(list)).toEqual([ 1, 2, 3, 0 ])
})

test('with object', () => {
  const list = [ { a : 1 }, { a : 2 }, { a : 1 }, { a : 2 } ]
  expect(uniq(list)).toEqual([ { a : 1 }, { a : 2 } ])
})

test('with nested array', () => {
  expect(uniq([ [ 42 ], [ 42 ] ])).toEqual([ [ 42 ] ])
})

test('with booleans', () => {
  expect(uniq([ [ false ], [ false ], [ true ] ])).toEqual([ [ false ], [ true ] ])
})

test('with falsy values', () => {
  expect(uniq([ undefined, null ])).toEqual([ undefined, null ])
})

test('can distinct between string and number', () => {
  expect(uniq([ 1, '1' ])).toEqual([ 1, '1' ])
})

import {uniq} from 'rambda'

describe('R.uniq', () => {
  it('happy', () => {
    const result = uniq([1, 2, 3, 3, 3, 1, 2, 0])
    result // $ExpectType number[]
  })
})

uniqBy

It applies uniqueness to input list based on function that defines what to be used for comparison between elements.

R.equals is used to determine equality.

Try this R.uniqBy example in Rambda REPL

uniqWith


uniqWith<T, U>(predicate: (x: T, y: T) => boolean, list: T[]): T[]

It returns a new array containing only one copy of each element in list according to predicate function.

This predicate should return true, if two elements are equal.

Try this R.uniqWith example in Rambda REPL

uniqWith<T, U>(predicate: (x: T, y: T) => boolean, list: T[]): T[];
uniqWith<T, U>(predicate: (x: T, y: T) => boolean): (list: T[]) => T[];

function includesWith(
  predicate, target, list
){
  let willReturn = false
  let index = -1

  while (++index < list.length && !willReturn){
    const value = list[ index ]

    if (predicate(target, value)){
      willReturn = true
    }
  }

  return willReturn
}

export function uniqWith(predicate, list){
  if (arguments.length === 1) return _list => uniqWith(predicate, _list)

  let index = -1
  const willReturn = []

  while (++index < list.length){
    const value = list[ index ]

    if (!includesWith(
      predicate, value, willReturn
    )){
      willReturn.push(value)
    }
  }

  return willReturn
}

import { uniqWith as uniqWithRamda } from 'ramda'

import { uniqWith } from './uniqWith.js'

const list = [ { a : 1 }, { a : 1 } ]

test('happy', () => {
  const fn = (x, y) => x.a === y.a

  const result = uniqWith(fn, list)
  expect(result).toEqual([ { a : 1 } ])
})

test('with list of strings', () => {
  const fn = (x, y) => x.length === y.length
  const list = [ '0', '11', '222', '33', '4', '55' ]
  const result = uniqWith(fn)(list)
  const resultRamda = uniqWithRamda(fn, list)
  expect(result).toEqual([ '0', '11', '222' ])
  expect(resultRamda).toEqual([ '0', '11', '222' ])
})

import {uniqWith} from 'rambda'

describe('R.uniqWith', () => {
  it('happy', () => {
    const list = [{a: 1}, {a: 1}]

    const fn = (x: any, y: any) => x.a === y.a

    const result = uniqWith(fn, list)
    result // $ExpectType { a: number; }[]
  })
})

unless


unless<T, U>(predicate: (x: T) => boolean, whenFalseFn: (x: T) => U, x: T): T | U

The method returns function that will be called with argument input.

If predicate(input) returns false, then the end result will be the outcome of whenFalse(input).

In the other case, the final output will be the input itself.

Try this R.unless example in Rambda REPL

unless<T, U>(predicate: (x: T) => boolean, whenFalseFn: (x: T) => U, x: T): T | U;
unless<T, U>(predicate: (x: T) => boolean, whenFalseFn: (x: T) => U): (x: T) => T | U;
unless<T>(predicate: (x: T) => boolean, whenFalseFn: (x: T) => T, x: T): T;
unless<T>(predicate: (x: T) => boolean, whenFalseFn: (x: T) => T): (x: T) => T;

import { curry } from './curry.js'

function unlessFn(
  predicate, whenFalseFn, input
){
  if (predicate(input)) return input

  return whenFalseFn(input)
}

export const unless = curry(unlessFn)

import { inc } from './inc.js'
import { isNil } from './isNil.js'
import { unless } from './unless.js'

test('happy', () => {
  const safeInc = unless(isNil, inc)
  expect(safeInc(null)).toBeNull()
  expect(safeInc(1)).toBe(2)
})

test('curried', () => {
  const safeIncCurried = unless(isNil)(inc)
  expect(safeIncCurried(null)).toBeNull()
})

test('with 3 inputs', () => {
  let result = unless(x => x.startsWith('/'), x=> x.concat('/'), '/api')
  expect(result).toBe('/api')
})

import {unless, inc} from 'rambda'

describe('R.unless', () => {
  it('happy', () => {
    const fn = unless(x => x > 5, inc)
    const result = fn(1)
    result // $ExpectType number
  })
  it('with one explicit type', () => {
    const result = unless(
      x => {
        x // $ExpectType number
        return x > 5
      },
      x => {
        x // $ExpectType number
        return x + 1
      },
      1
    )
    result // $ExpectType number
  })
  it('with two different explicit types', () => {
    const result = unless(
      x => {
        x // $ExpectType number
        return x > 5
      },
      x => {
        x // $ExpectType number
        return `${x}-foo`
      },
      1
    )
    result // $ExpectType string | number
  })
})

describe('R.unless - curried', () => {
  it('happy', () => {
    const fn = unless(x => x > 5, inc)
    const result = fn(1)
    result // $ExpectType number
  })
  it('with one explicit type', () => {
    const fn = unless<number>(
      x => {
        x // $ExpectType number
        return x > 5
      },
      x => {
        x // $ExpectType number
        return x + 1
      }
    )
    const result = fn(1)
    result // $ExpectType number
  })
  it('with two different explicit types', () => {
    const fn = unless<number, string>(
      x => {
        x // $ExpectType number
        return x > 5
      },
      x => {
        x // $ExpectType number
        return `${x}-foo`
      }
    )
    const result = fn(1)
    result // $ExpectType string | number
  })
})

unnest

Try this R.unnest example in Rambda REPL

unwind

Try this R.unwind example in Rambda REPL

update


update<T>(index: number, newValue: T, list: T[]): T[]

It returns a copy of list with updated element at index with newValue.

Try this R.update example in Rambda REPL

update<T>(index: number, newValue: T, list: T[]): T[];
update<T>(index: number, newValue: T): (list: T[]) => T[];

import { cloneList } from './_internals/cloneList.js'
import { curry } from './curry.js'

export function updateFn(
  index, newValue, list
){
  const clone = cloneList(list)
  if (index === -1) return clone.fill(newValue, index)

  return clone.fill(
    newValue, index, index + 1
  )
}

export const update = curry(updateFn)

import { update } from './update.js'

const list = [ 1, 2, 3 ]

test('happy', () => {
  const newValue = 8
  const index = 1
  const result = update(
    index, newValue, list
  )
  const curriedResult = update(index, newValue)(list)
  const tripleCurriedResult = update(index)(newValue)(list)

  const expected = [ 1, 8, 3 ]
  expect(result).toEqual(expected)
  expect(curriedResult).toEqual(expected)
  expect(tripleCurriedResult).toEqual(expected)
})

test('list has no such index', () => {
  const newValue = 8
  const index = 10
  const result = update(
    index, newValue, list
  )

  expect(result).toEqual(list)
})

test('with negative index', () => {
  expect(update(
    -1, 10, [ 1 ]
  )).toEqual([ 10 ])
  expect(update(
    -1, 10, []
  )).toEqual([])
  expect(update(
    -1, 10, list
  )).toEqual([ 1, 2, 10 ])
  expect(update(
    -2, 10, list
  )).toEqual([ 1, 10, 3 ])
  expect(update(
    -3, 10, list
  )).toEqual([ 10, 2, 3 ])
})

import {update} from 'rambda'

describe('R.update', () => {
  it('happy', () => {
    const result = update(1, 0, [1, 2, 3])
    result // $ExpectType number[]
  })
})

values


values<T extends object, K extends keyof T>(obj: T): T[K][]

With correct input, this is nothing more than Object.values(Record<string, unknown>). If obj is not an object, then it returns an empty array.

Try this R.values example in Rambda REPL

values<T extends object, K extends keyof T>(obj: T): T[K][];

import { type } from './type.js'

export function values(obj){
  if (type(obj) !== 'Object') return []
  return Object.values(obj)
}

import { values } from './values.js'

test('happy', () => {
  expect(values({
    a : 1,
    b : 2,
    c : 3,
  })).toEqual([ 1, 2, 3 ])
})

test('with bad input', () => {
  expect(values(null)).toEqual([])
  expect(values(undefined)).toEqual([])
  expect(values(55)).toEqual([])
  expect(values('foo')).toEqual([])
  expect(values(true)).toEqual([])
  expect(values(false)).toEqual([])
  expect(values(NaN)).toEqual([])
  expect(values(Infinity)).toEqual([])
  expect(values([])).toEqual([])
})

import {values} from 'rambda'

describe('R.values', () => {
  it('happy', () => {
    const result = values({
      a: 1,
      b: 2,
      c: 3,
    })
    result // $ExpectType number[]
  })
})

view


view<S, A>(lens: Lens<S, A>): (obj: S) => A

It returns the value of lens focus over target object.

Try this R.view example in Rambda REPL

view<S, A>(lens: Lens<S, A>): (obj: S) => A;
view<S, A>(lens: Lens<S, A>, obj: S): A;

const Const = x => ({
  x,
  map : fn => Const(x),
})

export function view(lens, target){
  if (arguments.length === 1) return _target => view(lens, _target)

  return lens(Const)(target).x
}

import { assoc } from './assoc.js'
import { lens } from './lens.js'
import { prop } from './prop.js'
import { view } from './view.js'

const testObject = { foo : 'Led Zeppelin' }
const assocLens = lens(prop('foo'), assoc('foo'))

test('happy', () => {
  expect(view(assocLens, testObject)).toBe('Led Zeppelin')
})

when


when<T, U>(predicate: (x: T) => boolean, whenTrueFn: (a: T) => U, input: T): T | U

It pass input to predicate function and if the result is true, it will return the result of whenTrueFn(input). If the predicate returns false, then it will simply return input.

Try this R.when example in Rambda REPL

when<T, U>(predicate: (x: T) => boolean, whenTrueFn: (a: T) => U, input: T): T | U;
when<T, U>(predicate: (x: T) => boolean, whenTrueFn: (a: T) => U): (input: T) => T | U;
when<T, U>(predicate: (x: T) => boolean): ((whenTrueFn: (a: T) => U) => (input: T) => T | U);

import { curry } from './curry.js'

function whenFn(
  predicate, whenTrueFn, input
){
  if (!predicate(input)) return input

  return whenTrueFn(input)
}

export const when = curry(whenFn)

import { add } from './add.js'
import { when } from './when.js'

const predicate = x => typeof x === 'number'

test('happy', () => {
  const fn = when(predicate, add(11))
  expect(fn(11)).toBe(22)
  expect(fn('foo')).toBe('foo')
})

import {when} from 'rambda'

const predicate = (x: number) => x > 2
const whenTrueFn = (x: number) => String(x)

describe('R.when', () => {
  it('happy', () => {
    const result = when(predicate, whenTrueFn, 1)
    result // $ExpectType string | 1
  })

  it('curry 1', () => {
    const fn = when(predicate, whenTrueFn)
    const result = fn(1)
    result // $ExpectType string | number
  })

  it('curry 2 require explicit types', () => {
    const fn = when<number, string>(predicate)(whenTrueFn)
    const result = fn(1)
    result // $ExpectType string | number
  })
})

where


where<T, U>(conditions: T, input: U): boolean

It returns true if all each property in conditions returns true when applied to corresponding property in input object.

Try this R.where example in Rambda REPL

where<T, U>(conditions: T, input: U): boolean;
where<T>(conditions: T): <U>(input: U) => boolean;
where<ObjFunc2, U>(conditions: ObjFunc2, input: U): boolean;
where<ObjFunc2>(conditions: ObjFunc2): <U>(input: U) => boolean;

export function where(conditions, input){
  if (input === undefined){
    return _input => where(conditions, _input)
  }
  let flag = true
  for (const prop in conditions){
    if (!flag) continue
    const result = conditions[ prop ](input[ prop ])
    if (flag && result === false){
      flag = false
    }
  }

  return flag
}

import { equals } from './equals.js'
import { where } from './where.js'

test('when true', () => {
  const result = where({
    a : equals('foo'),
    b : equals('bar'),
  },
  {
    a : 'foo',
    b : 'bar',
    x : 11,
    y : 19,
  })

  expect(result).toBeTrue()
})

test('when false | early exit', () => {
  let counter = 0
  const equalsFn = expected => input => {
    console.log(expected, 'expected')
    counter++

    return input === expected
  }
  const predicate = where({
    a : equalsFn('foo'),
    b : equalsFn('baz'),
  })
  expect(predicate({
    a : 'notfoo',
    b : 'notbar',
  })).toBeFalse()
  expect(counter).toBe(1)
})

import {where, equals} from 'rambda'

describe('R.where', () => {
  it('happy', () => {
    const input = {
      a: 'foo',
      b: 'bar',
      x: 11,
      y: 19,
    }
    const conditions = {
      a: equals('foo'),
      b: equals('bar'),
    }
    const result = where(conditions, input)
    const curriedResult = where(conditions)(input)
    result // $ExpectType boolean
    curriedResult // $ExpectType boolean
  })
})

whereAny

Same as R.where, but it will return true if at least one condition check returns true.

Try this R.whereAny example in Rambda REPL

whereEq


whereEq<T, U>(condition: T, input: U): boolean

It will return true if all of input object fully or partially include rule object.

R.equals is used to determine equality.

Try this R.whereEq example in Rambda REPL

whereEq<T, U>(condition: T, input: U): boolean;
whereEq<T>(condition: T): <U>(input: U) => boolean;

import { equals } from './equals.js'
import { filter } from './filter.js'

export function whereEq(condition, input){
  if (arguments.length === 1){
    return _input => whereEq(condition, _input)
  }

  const result = filter((conditionValue, conditionProp) =>
    equals(conditionValue, input[ conditionProp ]),
  condition)

  return Object.keys(result).length === Object.keys(condition).length
}

import { whereEq } from './whereEq.js'

test('when true', () => {
  const condition = { a : 1 }
  const input = {
    a : 1,
    b : 2,
  }

  const result = whereEq(condition, input)
  const expectedResult = true

  expect(result).toEqual(expectedResult)
})

test('when false', () => {
  const condition = { a : 1 }
  const input = { b : 2 }

  const result = whereEq(condition, input)
  const expectedResult = false

  expect(result).toEqual(expectedResult)
})

test('with nested object', () => {
  const condition = { a : { b : 1 } }
  const input = {
    a : { b : 1 },
    c : 2,
  }

  const result = whereEq(condition)(input)
  const expectedResult = true

  expect(result).toEqual(expectedResult)
})

test('with wrong input', () => {
  const condition = { a : { b : 1 } }

  expect(() => whereEq(condition, null)).toThrowErrorMatchingInlineSnapshot('"Cannot read properties of null (reading \'a\')"')
})

import {whereEq} from 'rambda'

describe('R.whereEq', () => {
  it('happy', () => {
    const result = whereEq({a: {b: 2}}, {b: 2})
    const curriedResult = whereEq({a: {b: 2}})({b: 2})
    result // $ExpectType boolean
    curriedResult // $ExpectType boolean
  })
})

without


without<T>(matchAgainst: T[], source: T[]): T[]

It will return a new array, based on all members of source list that are not part of matchAgainst list.

R.equals is used to determine equality.

Try this R.without example in Rambda REPL

without<T>(matchAgainst: T[], source: T[]): T[];
without<T>(matchAgainst: T[]): (source: T[]) => T[];

import { _indexOf } from './equals.js'
import { reduce } from './reduce.js'

export function without(matchAgainst, source){
  if (source === undefined){
    return _source => without(matchAgainst, _source)
  }

  return reduce(
    (prev, current) =>
      _indexOf(current, matchAgainst) > -1 ? prev : prev.concat(current),
    [],
    source
  )
}

import { without as withoutRamda } from 'ramda'

import { without } from './without.js'

test('should return a new list without values in the first argument', () => {
  const itemsToOmit = [ 'A', 'B', 'C' ]
  const collection = [ 'A', 'B', 'C', 'D', 'E', 'F' ]

  expect(without(itemsToOmit, collection)).toEqual([ 'D', 'E', 'F' ])
  expect(without(itemsToOmit)(collection)).toEqual([ 'D', 'E', 'F' ])
})

test('with list of objects', () => {
  const itemsToOmit = [ { a : 1 }, { c : 3 } ]
  const collection = [ { a : 1 }, { b : 2 }, { c : 3 }, { d : 4 } ]
  const expected = [ { b : 2 }, { d : 4 } ]

  expect(without(itemsToOmit, collection)).toEqual(expected)
  expect(withoutRamda(itemsToOmit, collection)).toEqual(expected)
})

test('ramda accepts string as target input while rambda throws', () => {
  expect(withoutRamda('0:1', [ '0', '0:1' ])).toEqual([ '0:1' ])
  expect(() =>
    without('0:1', [ '0', '0:1' ])).toThrowErrorMatchingInlineSnapshot('"Cannot read property \'indexOf\' of 0:1"')
  expect(without([ '0:1' ], [ '0', '0:1' ])).toEqual([ '0' ])
})

test('ramda test', () => {
  expect(without([ 1, 2 ])([ 1, 2, 1, 3, 4 ])).toEqual([ 3, 4 ])
})

import {without} from 'rambda'

const itemsToOmit = ['A', 'B', 'C']
const collection = ['A', 'B', 'C', 'D', 'E', 'F']

describe('R.without', () => {
  it('happy', () => {
    const result = without(itemsToOmit, collection)

    result // $ExpectType string[]
  })
  it('curried', () => {
    const result = without(itemsToOmit)(collection)

    result // $ExpectType string[]
  })
})

xor


xor(x: boolean, y: boolean): boolean

Logical XOR

Try this R.xor example in Rambda REPL

xor(x: boolean, y: boolean): boolean;
xor(y: boolean): (y: boolean) => boolean;

export function xor(a, b){
  if (arguments.length === 1) return _b => xor(a, _b)

  return Boolean(a) && !b || Boolean(b) && !a
}

import { xor } from './xor.js'

test('compares two values with exclusive or', () => {
  expect(xor(true, true)).toBeFalse()
  expect(xor(true, false)).toBeTrue()
  expect(xor(false, true)).toBeTrue()
  expect(xor(false, false)).toBeFalse()
})

test('when both values are truthy, it should return false', () => {
  expect(xor(true, 'foo')).toBeFalse()
  expect(xor(42, true)).toBeFalse()
  expect(xor('foo', 42)).toBeFalse()
  expect(xor({}, true)).toBeFalse()
  expect(xor(true, [])).toBeFalse()
  expect(xor([], {})).toBeFalse()
  expect(xor(new Date(), true)).toBeFalse()
  expect(xor(true, Infinity)).toBeFalse()
  expect(xor(Infinity, new Date())).toBeFalse()
})

test('when both values are falsy, it should return false', () => {
  expect(xor(null, false)).toBeFalse()
  expect(xor(false, undefined)).toBeFalse()
  expect(xor(undefined, null)).toBeFalse()
  expect(xor(0, false)).toBeFalse()
  expect(xor(false, NaN)).toBeFalse()
  expect(xor(NaN, 0)).toBeFalse()
  expect(xor('', false)).toBeFalse()
})

test('when one argument is truthy and the other is falsy, it should return true', () => {
  expect(xor('foo', null)).toBeTrue()
  expect(xor(null, 'foo')).toBeTrue()
  expect(xor(undefined, 42)).toBeTrue()
  expect(xor(42, undefined)).toBeTrue()
  expect(xor(Infinity, NaN)).toBeTrue()
  expect(xor(NaN, Infinity)).toBeTrue()
  expect(xor({}, '')).toBeTrue()
  expect(xor('', {})).toBeTrue()
  expect(xor(new Date(), 0)).toBeTrue()
  expect(xor(0, new Date())).toBeTrue()
  expect(xor([], null)).toBeTrue()
  expect(xor(undefined, [])).toBeTrue()
})

import {xor} from 'rambda'

describe('R.xor', () => {
  it('happy', () => {
    xor(true, false) // $ExpectType boolean
  })
  it('curry', () => {
    xor(true)(false) // $ExpectType boolean
  })
})

zip


zip<K, V>(x: K[], y: V[]): KeyValuePair<K, V>[]

It will return a new array containing tuples of equally positions items from both x and y lists.

The returned list will be truncated to match the length of the shortest supplied list.

Try this R.zip example in Rambda REPL

zip<K, V>(x: K[], y: V[]): KeyValuePair<K, V>[];
zip<K>(x: K[]): <V>(y: V[]) => KeyValuePair<K, V>[];

export function zip(left, right){
  if (arguments.length === 1) return _right => zip(left, _right)

  const result = []
  const length = Math.min(left.length, right.length)

  for (let i = 0; i < length; i++){
    result[ i ] = [ left[ i ], right[ i ] ]
  }

  return result
}

import { zip } from './zip.js'

const array1 = [ 1, 2, 3 ]
const array2 = [ 'A', 'B', 'C' ]

test('should return an array', () => {
  const actual = zip(array1)(array2)
  expect(actual).toBeInstanceOf(Array)
})

test('should return and array or tuples', () => {
  const expected = [
    [ 1, 'A' ],
    [ 2, 'B' ],
    [ 3, 'C' ],
  ]
  const actual = zip(array1, array2)
  expect(actual).toEqual(expected)
})

test('should truncate result to length of shorted input list', () => {
  const expectedA = [
    [ 1, 'A' ],
    [ 2, 'B' ],
  ]
  const actualA = zip([ 1, 2 ], array2)
  expect(actualA).toEqual(expectedA)

  const expectedB = [
    [ 1, 'A' ],
    [ 2, 'B' ],
  ]
  const actualB = zip(array1, [ 'A', 'B' ])
  expect(actualB).toEqual(expectedB)
})

import {zip} from 'rambda'

describe('R.zip', () => {
  it('happy', () => {
    const array1 = [1, 2, 3]
    const array2 = ['A', 'B', 'C']

    const result = zip(array1)(array2)
    result // $ExpectType KeyValuePair<number, string>[]
  })
})

zipObj


zipObj<T, K extends string>(keys: K[], values: T[]): { [P in K]: T }

It will return a new object with keys of keys array and values of values array.

Try this R.zipObj example in Rambda REPL

zipObj<T, K extends string>(keys: K[], values: T[]): { [P in K]: T };
zipObj<K extends string>(keys: K[]): <T>(values: T[]) => { [P in K]: T };
zipObj<T, K extends number>(keys: K[], values: T[]): { [P in K]: T };
zipObj<K extends number>(keys: K[]): <T>(values: T[]) => { [P in K]: T };

import { take } from './take.js'

export function zipObj(keys, values){
  if (arguments.length === 1) return yHolder => zipObj(keys, yHolder)

  return take(values.length, keys).reduce((
    prev, xInstance, i
  ) => {
    prev[ xInstance ] = values[ i ]

    return prev
  }, {})
}

import { equals } from './equals.js'
import { zipObj } from './zipObj.js'

test('zipObj', () => {
  expect(zipObj([ 'a', 'b', 'c' ], [ 1, 2, 3 ])).toEqual({
    a : 1,
    b : 2,
    c : 3,
  })
})

test('0', () => {
  expect(zipObj([ 'a', 'b' ])([ 1, 2, 3 ])).toEqual({
    a : 1,
    b : 2,
  })
})

test('1', () => {
  expect(zipObj([ 'a', 'b', 'c' ])([ 1, 2 ])).toEqual({
    a : 1,
    b : 2,
  })
})

test('ignore extra keys', () => {
  const result = zipObj([ 'a', 'b', 'c', 'd', 'e', 'f' ], [ 1, 2, 3 ])
  const expected = {
    a : 1,
    b : 2,
    c : 3,
  }

  expect(equals(result, expected)).toBeTrue()
})

import {zipObj} from 'rambda'

describe('R.zipObj', () => {
  it('happy', () => {
    // this is wrong since 24.10.2020 `@types/ramda` changes
    const result = zipObj(['a', 'b', 'c', 'd'], [1, 2, 3])
    ;[result.a, result.b, result.c, result.d] // $ExpectType number[]
  })
  it('imported from @types/ramda', () => {
    const result = zipObj(['a', 'b', 'c'], [1, 2, 3])
    const curriedResult = zipObj(['a', 'b', 'c'])([1, 2, 3])
    ;[result.a, result.b, result.c] // $ExpectType number[]
    ;[curriedResult.a, curriedResult.b, curriedResult.c] // $ExpectType number[]
  })
})

zipWith


zipWith<T, U, TResult>(fn: (x: T, y: U) => TResult, list1: T[], list2: U[]): TResult[]

Try this R.zipWith example in Rambda REPL

zipWith<T, U, TResult>(fn: (x: T, y: U) => TResult, list1: T[], list2: U[]): TResult[];
zipWith<T, U, TResult>(fn: (x: T, y: U) => TResult, list1: T[]): (list2: U[]) => TResult[];
zipWith<T, U, TResult>(fn: (x: T, y: U) => TResult): (list1: T[], list2: U[]) => TResult[];

import { curry } from './curry.js'
import { take } from './take.js'

function zipWithFn(
  fn, x, y
){
  return take(x.length > y.length ? y.length : x.length, x).map((xInstance, i) => fn(xInstance, y[ i ]))
}

export const zipWith = curry(zipWithFn)

import { add } from './add.js'
import { zipWith } from './zipWith.js'

const list1 = [ 1, 2, 3 ]
const list2 = [ 10, 20, 30, 40 ]
const list3 = [ 100, 200 ]

test('when second list is shorter', () => {
  const result = zipWith(
    add, list1, list3
  )
  expect(result).toEqual([ 101, 202 ])
})

test('when second list is longer', () => {
  const result = zipWith(
    add, list1, list2
  )
  expect(result).toEqual([ 11, 22, 33 ])
})

import {zipWith} from 'rambda'

const list1 = [1, 2]
const list2 = [10, 20, 30]

describe('R.zipWith', () => {
  it('happy', () => {
    const result = zipWith(
      (x, y) => {
        x // $ExpectType number
        y // $ExpectType number
        return `${x}-${y}`
      },
      list1,
      list2
    )

    result // $ExpectType string[]
  })
  it('curried', () => {
    const result = zipWith((x, y) => {
      x // $ExpectType unknown
      y // $ExpectType unknown
      return `${x}-${y}`
    })(list1, list2)

    result // $ExpectType string[]
  })
})

CHANGELOG

9.3.0

Breaking change in relation to TS typings of R.assoc, R.dissoc and R.modify - https://github.com/ramda/types/pull/37
Add R.isNotEmpty as it is new method in Ramda
Fix R.head/R.last TS definition - It returns undefined if array has length of 0. Before

9.2.1

Broken Deno build - Issue #731

9.2.0

R.once TS type definition miss to context argument and its type - Issue #728
Fix implementation of R.unless function - https://github.com/selfrefactor/rambda/pull/726

9.1.1

Faster R.equals with Object.is short circuit - https://github.com/selfrefactor/rambda/pull/725
Fix R.cond transform is unary - https://github.com/selfrefactor/rambda/issues/720

9.1.0

Add these methods

insert
insertAll
lt
lte
isNotNil
pickBy
pathSatisfies
swap
mergeDeepLeft

9.0.1

Fix bad TS typings, due to missing declaration - Issue #716

9.0.0

Breaking change in TS definitions of lenses as now they are synced to Ramda types.

Add R.sortWith - Issue #707
Add R.innerJoin, R.gt, R.gte, R.reduceBy, R.hasIn

8.6.0

Wrong typing for R.dissocPath - Issue #709
Update build dependencies

8.5.0

Revert changes in R.anyPass introduced in 8.4.0 release. The reason is that the change was breaking the library older than 5.2.0 TypeScript.
Wrong R.partial TS definition - Issue #705
Add R.dropRepeatsBy
Add R.empty
Add R.eqBy
Add R.forEachObjIndexed

8.4.0

Add R.dissocPath
Fix TS definitions of R.head/R.last and add missing handle of empty string
Add R.removeIndex - method was before only in Rambdax, but now since R.dissocPath is using it, it is added to main library.
Allow R.omit to pass numbers as part of properties to omit, i.e. R.omit(['a', 1], {a: {1: 1, 2: 2}})
R.keys always returns strings - MR #700
Improve R.prepend/R.append type interference - MR #699
Change R.reduce TS definitions so index is always received - MR #696
Functions as a type guard in R.anyPass TS definitions - MR #695
Fix R.append's curried type - MR #694
Fix cannot compare errors in Deno with R.equals - Issue #704.
Fix cannot compare BigInt with R.equals

8.3.0

Add the following methods:

binary
call
collectBy
comparator
composeWith

8.2.0

Add the following methods:

addIndex
addIndexRight
ap
aperture
applyTo
ascend
descend

8.1.0

Fix input order of TS definitions for R.propEq method - Issue #688. The issue was due to 8.0.0 was shipped with TS definitions of 7.5.0 release.
Add R.differenceWith method - Issue #91

8.0.0

handle falsy values in merge methods - https://github.com/ramda/ramda/pull/3222
R.head/R.last don't return undefined for non-empty arrays
R.type supports dates in TS definition - Rambda already did support dates in JS.
Improve typings of R.endsWith/startsWith with regard to string input. - PR #622
Handle list as falsy value in R.reduce - Ramda MR
R.nop is removed - it will be moved to Rambdax as R.noop
R.includes is no longer using string literal in TypeScript definitions

Reason for breaking change - synchronize with Ramda 0.29.0 release:

change order of R.propEq - Ramda MR

7.5.0

IMPORTANT: Remove export property in package.json in order to allow Rambda support for projects with "type": "module" in package.json - Issue #667
Add R.unnest - Rambdax issue 89
R.uniq is not using R.equals as Ramda does - Issue #88
Fix R.path(['non','existing','path'], obj) TS definition as 7.4.0 release caused TS errors - Issue #668

7.4.0

Synchronize with @types/ramda - R.prop, R.path, R.pickAll
Remove esm Rollup output due to tree-shaking issues.
Upgrade all dev dependencies.

7.3.0

Important - changing import declaration in package.json in order to fix tree-shaking issue - Issue #647
Add R.modify
Allow multiple inputs in TypeScript versions of R.anyPass and R.allPass - Issue #642
Using wrong clone of object in R.mergeDeepRight - Issue #650
Missing early return in R.where - Issue #648
R.allPass doesn't accept more than 1 parameters for function predicates- Issue #604

7.2.1

Remove bad typings of R.propIs which caused the library to cannot be build with TypeScript.
Drop support for Wallaby as per https://github.com/wallabyjs/public/issues/3037

7.2.0

Wrong R.update if index is -1 - PR #593
Wrong curried typings in R.anyPass - Issue #642
R.modifyPath not exported - Issue #640
Add new method R.uniqBy. Implementation is coming from Ramda MR#2641
Apply the following changes from @types/rambda:

-- [https://github.com/DefinitelyTyped/DefinitelyTyped/commit/bab47272d52fc7bb81e85da36dbe9c905a04d067](add AnyFunction and AnyConstructor)

-- Improve R.ifElse typings - https://github.com/DefinitelyTyped/DefinitelyTyped/pull/59291

-- Make R.propEq safe for null/undefined arguments - https://github.com/ramda/ramda/pull/2594/files

7.1.4

R.mergeRight not found on Deno import - Issue #633

7.1.0

Add R.mergeRight - introduced by Ramda's latest release. While Ramda renames R.merge, Rambda will keep R.merge.
Rambda's pipe/compose doesn't return proper length of composed function which leads to issue with R.applySpec. It was fixed by using Ramda's pipe/compose logic - Issue #627
Replace Async with Promise as return type of R.type.
Add new types as TypeScript output for R.type - "Map", "WeakMap", "Generator", "GeneratorFunction", "BigInt", "ArrayBuffer"
Add R.juxt method
Add R.propSatisfies method
Add new methods after Ramda version upgrade to 0.28.0:

-- R.count -- R.modifyPath -- R.on -- R.whereAny -- R.partialObject

7.0.3

Rambda.none has wrong logic introduced in version 7.0.0 - Issue #625

7.0.2

Rambda doesn't work with pnpm due to wrong export configuration - Issue #619

7.0.1

Wrong ESM export configuration in package.json - Issue #614

7.0.0

Breaking change - sync R.compose/R.pipe with @types/ramda. That is significant change so as safeguard, it will lead a major bump. Important - this lead to raising required TypeScript version to 4.2.2. In other words, to use Rambda you'll need TypeScript version 4.2.2 or newer.

There are several other changes in @types/ramda as stated in this comment. This leads to change of typings for the following methods in Rambda:

-- R.unless

-- R.toString

-- R.ifElse

-- R.always

-- R.complement

-- R.cond

-- R.is

-- R.sortBy

-- R.dissoc

-- R.toPairs

-- R.assoc

-- R.toLower

-- R.toUpper

One more reason for the breaking change is changing of export declarations in package.json based on this blog post and this merged Ramda's PR. This also led to renaming of babel.config.js to babel.config.cjs.
Add R.apply, R.bind and R.unapply
R.startsWith/R.endsWith now support lists as inputs. This way, it matches current Ramda behavior.
Remove unused typing for R.chain.
R.map/R.filter no longer accept bad inputs as iterable. This way, Rambda behaves more like Ramda, which also throws.
Make R.lastIndexOf follow the logic of R.indexOf.
Change R.type logic to Ramda logic. This way, R.type can return Error and Set as results.
Add missing logic in R.equals to compare sets - Issue #599
Improve list cloning - Issue #595
Handle multiple inputs with R.allPass and R.anyPass - Issue #604
Fix R.length wrong logic with inputs as {length: 123} - Issue #606.
Improve non-curry typings of R.merge by using types from mobily/ts-belt.
Improve performance of R.uniqWith.
Wrong R.update if index is -1 - PR #593
Make R.eqProps safe for falsy inputs - based on this opened Ramda PR.
Incorrect benchmarks for R.pipe/R.compose - Issue #608
Fix R.last/R.head typings - Issue #609

6.9.0

Fix slow R.uniq methods - Issue #581

Fixing R.uniq was done by improving R.indexOf which has performance implication to all methods importing R.indexOf:

R.includes
R.intersection
R.difference
R.excludes
R.symmetricDifference
R.union
R.without no longer support the following case - without('0:1', ['0', '0:1']) // => ['0']. Now it throws as the first argument should be a list, not a string. Ramda, on the other hand, returns an empty list - https://github.com/ramda/ramda/issues/3086.

6.8.3

Fix TypeScript build process with rambda/immutable - Issue #572
Add R.objOf method
Add R.mapObjIndexed method
Publish shorter README.md version to NPM

6.8.0

R.has use Object.prototype.hasOwnProperty- Issue #572
Expose immutable.ts typings which are Rambda typings with readonly statements - Issue #565
Fix R.intersection wrong order compared to Ramda.
R.path wrong return of null instead of undefined when path value is null - PR #577

6.7.0

Remove ts-toolbelt types from TypeScript definitions. Most affected are the following methods, which lose one of its curried definitions:

R.maxBy
R.minBy
R.pathEq
R.viewOr
R.when
R.merge
R.mergeDeepRight
R.mergeLeft

6.6.0

Change R.piped typings to mimic that of R.pipe. Main difference is that R.pipe is focused on unary functions.
Fix wrong logic when R.without use R.includes while it should use array version of R.includes.
Use uglify plugin for UMD bundle.
Remove dist folder from .gitignore in order to fix Deno broken package. Issue #570
Improve R.fromPairs typings - Issue #567

6.5.3

Wrong logic where R.without use R.includes while it should use the array version of R.includes

This is Ramda bug, that Rambda also has before this release - https://github.com/ramda/ramda/issues/3086

6.5.2

Wrong R.defaultTo typings - changes introduced in v6.5.0 are missing their TS equivalent.
Update dependencies

6.5.1

Fix wrong versions in changelog

6.5.0

R.defaultTo no longer accepts infinite inputs, thus it follows Ramda implementation.
R.equals supports equality of functions.
R.pipe doesn't use R.compose.
Close Issue #561 - export several internal TS interfaces and types
Close Issue #559 - improve R.propOr typings
Add CHANGELOG.md file in release files list

This is only part of the changelog. You can read the full text in CHANGELOG.md file.

Additional info

Most influential contributors(in alphabetical order)

@farwayer - improving performance in R.find, R.filter; give the idea how to make benchmarks more reliable;
@thejohnfreeman - add R.assoc, R.chain;
@peeja - add several methods and fix mutiple issues; provides great MR documentation
@helmuthdu - add R.clone; help improve code style;
@jpgorman - add R.zip, R.reject, R.without, R.addIndex;
@ku8ar - add R.slice, R.propOr, R.identical, R.propIs and several math related methods; introduce the idea to display missing Ramda methods;
@romgrk - add R.groupBy, R.indexBy, R.findLast, R.findLastIndex;
@squidfunk - add R.assocPath, R.symmetricDifference, R.difference, R.intersperse;
@synthet1c - add all lenses methods; add R.applySpec, R.converge;
@vlad-zhukov - help with configuring Rollup, Babel; change export file to use ES module exports;