2.0.2 • Public • Published


A way to store/manage objects or models.

Unlike other tools this makes no assumptions about how it's going to be used or what type of models it is going to contain. This makes it a very flexible/useful tool for modeling all kinds of stuff.

It does not require underscore or jQuery, but instead makes it easy to extend with those methods if you'd like.

Part of the Ampersand.js toolkit for building clientside applications.


npm i ampersand-collection

massive flexibility

The collection is a fairly low-level tool, in that it's useful for any time you want to be able to store JS objects in an array.

In many ways it's simply an observable array of objects.

It emits events when models are added, removed, sorted and more. It also allows for merging in a set of objects into an existing collection and emitting change events appropriately. For a detailed overview of the events that are emitted by ampersand-collection, please refer to the Event Catalog on the AmpersandJS learn page.

If you extend it with a .model property that contains a constructor, the collection will ensure that objects that don't match that constructor are instantiated before being added to the collection.

For example:

var Collection = require('ampersand-collection');
// can just store plain objects
var basicCollection = new Collection([
    {name: 'larry'},
    {name: 'curly'},
    {name: 'moe'}

Adding ampersand-collection-rest-mixin and ampersand-collection-underscore-mixin.

var Collection = require('ampersand-collection');
var restMixin = require('ampersand-collection-rest-mixin');
var underscoreMixin = require('ampersand-collection-underscore-mixin');
// or we can extend it with underscore and REST methods
// to turn it into something similar to a Backbone Collection
var RestfulCollection = Collection.extend(underscoreMixin, restMixin, {
    url: '/mystuff'
var collection = new RestfulCollection();
// does ajax request

A quick note about instanceof checks

Because of module deps in npm and browserify, sometimes it’s possible to end up in a situation where the same collection constructor wasn't used to build a collection object. As a result, instanceof checks will fail.

To deal with this (because sometimes this is a legitimate scenario), collection simply creates a read-only isCollection property on all collection objects. You can use it to check whether or a not a given object is, in fact, a collection object—no matter what its constructor was.

API Reference

extend AmpersandCollection.extend([attributes])

Create a collection class of your own by extending AmpersandCollection, providing the required instance properties to be attached instances of your class.

Typically you will specify a model constructor (if you are storing ampersand-state or ampersand-model objects).

model collection.model

Override this property to specify the model class that the collection contains. If defined, you can pass raw attributes objects (and arrays) to add and reset, and the attributes will be converted into a model of the proper type.

var Library = AmpersandCollection.extend({
    model: Book

A collection can also contain polymorphic models by overriding this property with a function that returns a model.

Please note that if you do this, you'll also want to override the isModel method with your own, and describe the logic used to determine whether an object is already an instantiated model or not.

var Library = AmpersandCollection.extend({
  model: function(attrs, options) {
    if (condition) {
      return new PublicDocument(attrs, options);
    } else {
      return new PrivateDocument(attrs, options);
  isModel: function (model) {
    return model instanceof PublicDocument || model instanceof PrivateDocument;

constructor/initialize new AmpersandCollection([models [, options]])

When creating an AmpersandCollection, you may choose to pass in the initial array of models. The collection's comparator may be included as an option. If you define an initialize function, it will be invoked when the collection is created, with models and options as arguments. There are a couple of options that, if provided, are attached to the collection directly: model, comparator and parent.

var people = new AmpersandCollection([{ name: 'phil' }, { name: 'bob' }, { name: 'jane' }], {
    model: Person

mainIndex collection.mainIndex

Specify which property the collection should use as the main index (and unique identifier) for the models/objects it holds. This is the property that get uses to retrieve models, and what add, set, and remove uses to determine whether a collection already contains a model or not.

If you specify a model property in the collection, and the model specifies an idAttribute, the collection will use that as the mainIndex unless you explicitly set it to something else.

If no mainIndex or model is specified "id" is used as the default mainIndex.

This means, that most of the time you don't need to set mainIndex and things will still Just Work™. If you wish to index on a derived property, your derived fn must be a pure function, and will be bound to the object passed into the collection on .add()/.remove()/.set() etc.

You may set it explicitly while extending AmpersandCollection like so:

var People = AmpersandCollection.extend({
    mainIndex: '_id'

indexes collections.indexes

Specify an optional array of keys to serve as additional indexes for the models in your collection (in addition to mainIndex). This allows you to quickly retrieve models by specifying the key to use with get.

Note that get will only ever return a single model, so the values of these indexes should be unique across the models in the collection:

var People = AmpersandCollection.extend({
    mainIndex: '_id',
    indexes: ['otherId']
var people = new People([
    { _id: 1, otherId: 'a', name: 'Phil' },
    { _id: 2, otherId: 'b', name: 'Julie' },
    { _id: 3, otherId: 'c', name: 'Henrik' },
    { _id: 4, otherId: 'd', name: 'Jenn' }
people.get(1) //=> { _id: 1, otherId: 'a', name: 'Phil' }
people.get('b', 'otherId') //=> { _id: 2, otherId: 'b', name: 'Julie' },

length collection.length

Returns the length of the underlying array.

isCollection/instanceof collection.isCollection

Because of module deps in npm and browserify, sometimes it’s possible to end up in a situation where the same collection constructor wasn't used to build a collection object. As a result, instanceof checks will fail.

To deal with this (because sometimes this is a legitimate scenario), collection simply creates a read-only isCollection property on all collection objects. You can use it to check whether or a not a given object is, in fact, a collection object—no matter what its constructor was.

add collection.add(modelOrObject, [options])

Add a model (or an array of models) to the collection, firing an "add" event. If a model property is defined, you may also pass raw attributes objects, and have them be vivified as instances of the model. Returns the added models (or preexisting models, if already contained).


  • Pass {at: index} to splice the model into the collection at the specified index.
  • If you're adding models to the collection that it already contains, they'll be ignored, unless you pass {merge: true}, in which case their attributes will be merged into the corresponding models, firing any appropriate "change" events.
var ships = new AmpersandCollection();
ships.on("add", function(ship) {
  console.log("Ahoy " + + "!");
  {name: "Flying Dutchman"},
  {name: "Black Pearl"}
//- "Ahoy Flying Dutchman!"
//- "Ahoy Black Pearl!"

Note that adding the same model (a model with the same id) to a collection more than once is a no-op.

serialize collection.serialize()

Serialize the collection into a plain javascript array, ready for sending to the server (typically called via toJSON). Also calls serialize() on each model in the collection.

toJSON collection.toJSON()

Returns a plain javascript array of the models in the collection (which are also serialized), ready for sending to the server. The name of this method is a bit confusing, as it doesn't actually return a JSON string — but I'm afraid that it's the way that the JavaScript API for JSON.stringify() works.

var collection = new AmpersandCollection([
    {name: "Tim", age: 5},
    {name: "Ida", age: 26},
    {name: "Rob", age: 55}
//=> "[{\"name\":\"Tim\",\"age\":5},{\"name\":\"Ida\",\"age\":26},{\"name\":\"Rob\",\"age\":55}]"

parse collection.parse(data, [options])

The parse method gets called if the {parse: true} option is passed when calling collection.set method. By default, parse simply returns the data it was passed, but can be overwritten through .extend to provide any additional parsing logic to extract the array of data that should be stored in the collection. This is most commonly used when processing data coming back from an ajax request. The response from an API may look like this:

  "limit": 100,
  "offset": 0,
  "data": [
    {"name": "larry"},
    {"name": "curly"},
    {"name": "moe"}

To extract data you'd define a parse method on the collection as follows, to return the array of data to be stored.

var MyCollection = Collection.extend({
    parse: function (response) {

If you're using ampersand-rest-collection's fetch() method, the parse method will be called with the response by default. Also, the options object passed to set() gets passed through as a second argument to allow for conditional parsing logic.

set collection.set(models, [options])

The set method performs a "smart" update of the collection with the passed list of models:

  • If a model in the list isn't in the collection, it will be added.
  • If a model in the list is in the collection already, its attributes will be merged.
  • If the collection contains any models that aren't in the list, they'll be removed.

All of the appropriate "add", "remove", and "change" events are fired as this happens. If you'd like to customize the behavior, you can disable it with options: {add: false}, {remove: false}, or {merge: false}.

Returns the touched models in the collection.

var vanHalen = new AmpersandCollection([eddie, alex, stone, roth]);
vanHalen.set([eddie, alex, stone, hagar]);
// Fires a "remove" event for roth, and an "add" event for "hagar".
// Updates any of stone, alex, and eddie's attributes that may have
// changed over the years.

get collection.get(query, [indexName])

Retrieve a model from the collection by index.

If called without indexName (collection.get(123)), retrieves the model by its mainIndex attribute.

Alternatively, specify an indexName to retrieve a model by any of the other listed indexes.

var People = AmpersandCollection.extend({
    mainIndex: '_id',
    indexes: ['otherId']
var people = new People.add([
    { _id: 1, otherId: 'a', name: 'Phil' },
    { _id: 2, otherId: 'b', name: 'Julie' },
    { _id: 3, otherId: 'c', name: 'Henrik' },
    { _id: 4, otherId: 'd', name: 'Jenn' }
people.get(1) //=> { _id: 1, otherId: 'a', name: 'Phil' }
people.get('b', 'otherId') //=> { _id: 2, otherId: 'b', name: 'Julie' },


Get a model from a collection, specified by index. Useful if your collection is sorted.

If your collection isn't sorted, at() will still retrieve models in insertion order; e.g., returns the first model in the collection.

remove collection.remove(models, [options])

Remove a model (or an array of models) from the collection, and returns them. Fires a "remove" event, which you can use the option { silent: true } to suppress. The model's index before removal is available to listeners as options.index.

The models object/array can be references to actual models, or just a list of ids to remove.

reset collection.reset(models, [options])

Adding and removing models one at a time is all well and good, but sometimes there are so many models to change that you'd rather just update the collection in bulk. Use reset() to replace a collection with a new list of models (or attribute hashes), triggering a single "reset" event at the end. For convenience, within a "reset" event, the list of any previous models is available as options.previousModels.

Returns the newly-set models.

Calling collection.reset() without passing any models as arguments will empty the entire collection.

sort collection.sort([options])

Force a collection to re-sort itself. Triggers a "sort" event on the collection.

You don't need to call this under normal circumstances, as a collection with a comparator will sort itself whenever a model is added. To prevent this when adding a model, pass a {sort: false} option to add().

models collection.models

Raw access to the JavaScript array of models inside of the collection. Usually you'll want to use get, at, or the proxied array methods to access model objects, but occasionally a direct reference to the array is desired.


The comparator option lets you define how models in a collection are sorted. There's a few ways to declare comparator:

  • Passing false prevents sorting
  • Passing string sorts the collection by a specific model attribute
  • Passing function will use native array sort function; which you can define with either 1 argument (each model one by one), or multiple arguments (which lets you write custom compare functions with next 2 models as arguments).

proxied ES5 array methods (9)

The base AmpersandCollection proxies some basic ES5 methods to the underlying model array. Further documentation of these methods is available at MDN

  • indexOf
  • lastIndexOf
  • every
  • some
  • forEach
  • each (alias for forEach)
  • map
  • filter
  • reduce
  • reduceRight

Unlike Backbone collections, it does not include Underscore and all of its array methods. But if you want more functions than those built into modern browsers, you can mixin ampersand-collection-underscore-mixin to get them.

var people = People([
    { name: 'Phil', hatColor: 'red' },
    { name: 'Jenn', hatColor: 'green' },
    { name: 'Henrik', hatColor: 'blue' },
    { name: 'Julie', hatColor: 'yellow' }
]); (person) { return; }) //=> ['Phil', 'Jenn', 'Henrik', 'Julie']
people.filter(function (person) {
    return[0] === 'J';
}) //=> ['Jenn', 'Julie']


Created by @HenrikJoreteg, but many ideas and some code (especially for set()) should be credited to Jeremy Ashkenas and the rest of the Backbone.js authors.




  • 1.5.0 - add ability to index on a derived property



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