Lazily evaluates a getter on an object and caches the returned value
LGPL-3.0 License
Getter decorator that memoises the return value
npm install lazy-get-decorator
import {LazyGetter} from 'lazy-get-decorator';
class MyClass {
@LazyGetter(/* optional config */)
get foo(): number {
// ...
}
@LazyGetter(/* optional config */)
static get bar(): string {
// ...
}
}
All options are optional
Name | Type | Default | Description |
---|---|---|---|
global |
boolean |
false |
If set to true, the lazy getter triggering on one class instance will end up saving the returned value on all class instances, current and future. Has no effect on static getters. |
select |
<T, R>(this: T, output: R, self: T) => any |
A function to determine whether we should save the results (returning a truthy value) or continue calling the original getter (returning a falsy value). The default behaviour is to always save the 1st result. |
The following example will save the value only if the counter is 10
or above. The selector executes after the getter
function, hence the offset of 1: the current value of 9 is returned and passed on to the result selector, but the
counter value is already incremented at this point.
class MyClass {
#counter = 0;
@LazyGetter({select: v => v === 9})
get timesAccessed(): number {
return this.#counter++;
}
}
The library's only goal is to be compatible with Typescript 5 decorators which, at the time of writing, use the 2022-03 stage 3 decorators proposal. If you need experimental TS decorators or can't use a suitable Babel transform just stick to v2 - there are no new features in this release.
Typescript has further gotchas depending on the compiler target you've set.
ES2022 and higher allows you to use a class' method as a result selector:
class MyClass {
static shouldMemoiseStatic = false;
shouldMemoiseInstance = true;
@LazyGetter({select: MyClass.bar})
static get foo() {}
@LazyGetter({select: MyClass.prototype.bar2})
get foo2() {}
static bar() {
return this.shouldMemoiseStatic;
}
bar2() {
return this.shouldMemoiseInstance;
}
}
Attempting to do this on ES2021 or lower will result in a runtime error as of Typescript 5.2.
makeNonConfigurable
option removedsetProto
option renamed to global