Backbone Filters

Recycleable filters for Backbone collections. Create, bind, chain, and recycle your own!

// A collection
var myCollection = new MyCollection([
    { name: 'Cathcart' },
    { name: 'Yossarian' },
    { name: 'Peckem' },
    { name: 'Dreedle' }
]);

// A filter
var nameFilter = new Backbone.Filters.select(function (model) {
    var names = ['Cathcart', 'Peckem', 'Dreedle'];
    return names.indexOf(model.get('name')) > -1;
});

// Everyone but Yossarian
var results = myCollection.filter(nameFilter);

Or apply a list of filters in sequence!

var orderByNameFilter = new Backbone.Filters.sortBy(function (model) {
        return model.get('name');
    }),
    limit2 = new Backbone.Filters.first(2);

// Applying a filter chain
var filters = [
        nameFilter,        // Remove Yossarian
        orderByNameFilter, // Sort by name
        limit2             // Pick first two names
    ];
    
 var firstTwo = myCollection.filter(filters);

Using built-in filters

To create a filter based on one of the provided filter classes, just create new instances of filter with appropriate arguments. Passing the filter to a collection's filter method will return a new collection containing the filter's results. In this case, the first three items of the collection will be returned:

var random = new Backbone.Filters.shuffle,
    limit3 = new Backbone.Filters.first(3);

var first3 = myCollection.filter(limit3);
var entropized = myCollection.filter(random)

They can also be chained using array notation:

var random3 = myCollection.filter([random,limit3]);

Writing filter classes

Filters are derived from Backbone.Filter. They'll need to include a run method that accepts a single Backbone.Collection arguments, but the details of their implementation are left intentionally vague:

var MyFilterClass = Backbone.Filter.extend({
  run: function (collection) {
    // filter+return
  }
});

Filter chaining

Filters that don't reduce to a single value (e.g. the included Stats filters) will probably want to return an instance of the same Collection class that they received. As long as each filter in a chain returns a result that the next filter can understand, however, chains of filters will run to completion.

Included filters

To get things started, Backbone.Filter provides filter classes for many of the underscore methods. The ones attached to Backbone.Filters straight out of the box are:

filter
first
invoke
last
reject
select
shuffle
sortBy
without

A few other filters provide really basic statistical utilities for the attributes of models in a collection. By default, they're also attached to Backbone.Filters