Backbone.js

Backbone.Events

Events is a module that can be mixed in to any object, giving the object the ability to bind and trigger custom named events. Events do not have to be declared before they are bound, and may take passed arguments. For example:

var object = {};

_.extend(object, Backbone.Events);

object.on("alert", function(msg) {
  alert("Triggered " + msg);
});

object.trigger("alert", "an event");

For example, to make a handy event dispatcher that can coordinate events among different areas of your application: var dispatcher = _.clone(Backbone.Events)

onobject.on(event, callback, [context])Alias: bind
Bind a callback function to an object. The callback will be invoked whenever the event is fired. If you have a large number of different events on a page, the convention is to use colons to namespace them: "poll:start", or "change:selection". The event string may also be a space-delimited list of several events...

book.on("change:title change:author", ...);

Callbacks bound to the special "all" event will be triggered when any event occurs, and are passed the name of the event as the first argument. For example, to proxy all events from one object to another:

proxy.on("all", function(eventName) {
  object.trigger(eventName);
});

All Backbone event methods also support an event map syntax, as an alternative to positional arguments:

book.on({
  "change:author": authorPane.update,
  "change:title change:subtitle": titleView.update,
  "destroy": bookView.remove
});

To supply a context value for this when the callback is invoked, pass the optional last argument: model.on('change', this.render, this) or model.on({change: this.render}, this).

offobject.off([event], [callback], [context])Alias: unbind
Remove a previously-bound callback function from an object. If no context is specified, all of the versions of the callback with different contexts will be removed. If no callback is specified, all callbacks for the event will be removed. If no event is specified, callbacks for all events will be removed.

// Removes just the `onChange` callback.
object.off("change", onChange);

// Removes all "change" callbacks.
object.off("change");

// Removes the `onChange` callback for all events.
object.off(null, onChange);

// Removes all callbacks for `context` for all events.
object.off(null, null, context);

// Removes all callbacks on `object`.
object.off();

Note that calling model.off(), for example, will indeed remove all events on the model — including events that Backbone uses for internal bookkeeping.

triggerobject.trigger(event, [*args])
Trigger callbacks for the given event, or space-delimited list of events. Subsequent arguments to trigger will be passed along to the event callbacks.

onceobject.once(event, callback, [context])
Just like on, but causes the bound callback to fire only once before being removed. Handy for saying "the next time that X happens, do this". When multiple events are passed in using the space separated syntax, the event will fire once for every event you passed in, not once for a combination of all events

listenToobject.listenTo(other, event, callback)
Tell an object to listen to a particular event on an other object. The advantage of using this form, instead of other.on(event, callback, object), is that listenTo allows the object to keep track of the events, and they can be removed all at once later on. The callback will always be called with object as context.

view.listenTo(model, 'change', view.render);

stopListeningobject.stopListening([other], [event], [callback])
Tell an object to stop listening to events. Either call stopListening with no arguments to have the object remove all of its registered callbacks ... or be more precise by telling it to remove just the events it's listening to on a specific object, or a specific event, or just a specific callback.

view.stopListening();

view.stopListening(model);

listenToOnceobject.listenToOnce(other, event, callback)
Just like listenTo, but causes the bound callback to fire only once before being removed.

Catalog of Events
Here's the complete list of built-in Backbone events, with arguments. You're also free to trigger your own events on Models, Collections and Views as you see fit. The Backbone object itself mixes in Events, and can be used to emit any global events that your application needs.

"add" (model, collection, options) — when a model is added to a collection.
"remove" (model, collection, options) — when a model is removed from a collection.
"update" (collection, options) — single event triggered after any number of models have been added, removed or changed in a collection.
"reset" (collection, options) — when the collection's entire contents have been reset.
"sort" (collection, options) — when the collection has been re-sorted.
"change" (model, options) — when a model's attributes have changed.
"change:[attribute]" (model, value, options) — when a specific attribute has been updated.
"destroy" (model, collection, options) — when a model is destroyed.
"request" (model_or_collection, xhr, options) — when a model or collection has started a request to the server.
"sync" (model_or_collection, response, options) — when a model or collection has been successfully synced with the server.
"error" (model_or_collection, xhr, options) — when a model's or collection's request to the server has failed.
"invalid" (model, error, options) — when a model's validation fails on the client.
"route:[name]" (params) — Fired by the router when a specific route is matched.
"route" (route, params) — Fired by the router when any route has been matched.
"route" (router, route, params) — Fired by history when any route has been matched.
"all" — this special event fires for any triggered event, passing the event name as the first argument followed by all trigger arguments.

Generally speaking, when calling a function that emits an event (model.set, collection.add, and so on...), if you'd like to prevent the event from being triggered, you may pass {silent: true} as an option. Note that this is rarely, perhaps even never, a good idea. Passing through a specific flag in the options for your event callback to look at, and choose to ignore, will usually work out better.

Backbone.Model

Models are the heart of any JavaScript application, containing the interactive data as well as a large part of the logic surrounding it: conversions, validations, computed properties, and access control. You extend Backbone.Model with your domain-specific methods, and Model provides a basic set of functionality for managing changes.

The following is a contrived example, but it demonstrates defining a model with a custom method, setting an attribute, and firing an event keyed to changes in that specific attribute. After running this code once, sidebar will be available in your browser's console, so you can play around with it.

var Sidebar = Backbone.Model.extend({
  promptColor: function() {
    var cssColor = prompt("Please enter a CSS color:");
    this.set({color: cssColor});
  }
});

window.sidebar = new Sidebar;

sidebar.on('change:color', function(model, color) {
  $('#sidebar').css({background: color});
});

sidebar.set({color: 'white'});

sidebar.promptColor();

extendBackbone.Model.extend(properties, [classProperties])
To create a Model class of your own, you extend Backbone.Model and provide instance properties, as well as optional classProperties to be attached directly to the constructor function.

extend correctly sets up the prototype chain, so subclasses created with extend can be further extended and subclassed as far as you like.

var Note = Backbone.Model.extend({

  initialize: function() { ... },

  author: function() { ... },

  coordinates: function() { ... },

  allowedToEdit: function(account) {
    return true;
  }

});

var PrivateNote = Note.extend({

  allowedToEdit: function(account) {
    return account.owns(this);
  }

});

Brief aside on super: JavaScript does not provide a simple way to call super — the function of the same name defined higher on the prototype chain. If you override a core function like set, or save, and you want to invoke the parent object's implementation, you'll have to explicitly call it, along these lines:

var Note = Backbone.Model.extend({
  set: function(attributes, options) {
    Backbone.Model.prototype.set.apply(this, arguments);
    ...
  }
});

preinitializenew Model([attributes], [options])
For use with models as ES classes. If you define a preinitialize method, it will be invoked when the Model is first created, before any instantiation logic is run for the Model.

class Country extends Backbone.Model {
    preinitialize({countryCode}) {
      this.name = COUNTRY_NAMES[countryCode];
    }

    initialize() { ... }
}

constructor / initializenew Model([attributes], [options])
When creating an instance of a model, you can pass in the initial values of the attributes, which will be set on the model. If you define an initialize function, it will be invoked when the model is created.

new Book({
  title: "One Thousand and One Nights",
  author: "Scheherazade"
});

In rare cases, if you're looking to get fancy, you may want to override constructor, which allows you to replace the actual constructor function for your model.

var Library = Backbone.Model.extend({
  constructor: function() {
    this.books = new Books();
    Backbone.Model.apply(this, arguments);
  },
  parse: function(data, options) {
    this.books.reset(data.books);
    return data.library;
  }
});

If you pass a {collection: ...} as the options, the model gains a collection property that will be used to indicate which collection the model belongs to, and is used to help compute the model's url. The model.collection property is normally created automatically when you first add a model to a collection. Note that the reverse is not true, as passing this option to the constructor will not automatically add the model to the collection. Useful, sometimes.

If {parse: true} is passed as an option, the attributes will first be converted by parse before being set on the model.

getmodel.get(attribute)
Get the current value of an attribute from the model. For example: note.get("title")

setmodel.set(attributes, [options])
Set a hash of attributes (one or many) on the model. If any of the attributes change the model's state, a "change" event will be triggered on the model. Change events for specific attributes are also triggered, and you can bind to those as well, for example: change:title, and change:content. You may also pass individual keys and values.

note.set({title: "March 20", content: "In his eyes she eclipses..."});

book.set("title", "A Scandal in Bohemia");

escapemodel.escape(attribute)
Similar to get, but returns the HTML-escaped version of a model's attribute. If you're interpolating data from the model into HTML, using escape to retrieve attributes will prevent XSS attacks.

var hacker = new Backbone.Model({
  name: "<script>alert('xss')</script>"
});

alert(hacker.escape('name'));

hasmodel.has(attribute)
Returns true if the attribute is set to a non-null or non-undefined value.

if (note.has("title")) {
  ...
}

unsetmodel.unset(attribute, [options])
Remove an attribute by deleting it from the internal attributes hash. Fires a "change" event unless silent is passed as an option.

clearmodel.clear([options])
Removes all attributes from the model, including the id attribute. Fires a "change" event unless silent is passed as an option.

idmodel.id
A special property of models, the id is an arbitrary string (integer id or UUID). If you set the id in the attributes hash, it will be copied onto the model as a direct property. model.id should not be manipulated directly, it should be modified only via model.set('id', …). Models can be retrieved by id from collections, and the id is used to generate model URLs by default.

idAttributemodel.idAttribute
A model's unique identifier is stored under the id attribute. If you're directly communicating with a backend (CouchDB, MongoDB) that uses a different unique key, you may set a Model's idAttribute to transparently map from that key to id.

var Meal = Backbone.Model.extend({
  idAttribute: "_id"
});

var cake = new Meal({ _id: 1, name: "Cake" });
alert("Cake id: " + cake.id);

cidmodel.cid
A special property of models, the cid or client id is a unique identifier automatically assigned to all models when they're first created. Client ids are handy when the model has not yet been saved to the server, and does not yet have its eventual true id, but already needs to be visible in the UI.

attributesmodel.attributes
The attributes property is the internal hash containing the model's state — usually (but not necessarily) a form of the JSON object representing the model data on the server. It's often a straightforward serialization of a row from the database, but it could also be client-side computed state.

Please use set to update the attributes instead of modifying them directly. If you'd like to retrieve and munge a copy of the model's attributes, use _.clone(model.attributes) instead.

Due to the fact that Events accepts space separated lists of events, attribute names should not include spaces.

changedmodel.changed
The changed property is the internal hash containing all the attributes that have changed since its last set. Please do not update changed directly since its state is internally maintained by set. A copy of changed can be acquired from changedAttributes.

defaultsmodel.defaults or model.defaults()
The defaults hash (or function) can be used to specify the default attributes for your model. When creating an instance of the model, any unspecified attributes will be set to their default value.

var Meal = Backbone.Model.extend({
  defaults: {
    "appetizer":  "caesar salad",
    "entree":     "ravioli",
    "dessert":    "cheesecake"
  }
});

alert("Dessert will be " + (new Meal).get('dessert'));

Remember that in JavaScript, objects are passed by reference, so if you include an object as a default value, it will be shared among all instances. Instead, define defaults as a function.

toJSONmodel.toJSON([options])
Return a shallow copy of the model's attributes for JSON stringification. This can be used for persistence, serialization, or for augmentation before being sent 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 artist = new Backbone.Model({
  firstName: "Wassily",
  lastName: "Kandinsky"
});

artist.set({birthday: "December 16, 1866"});

alert(JSON.stringify(artist));

syncmodel.sync(method, model, [options])
Uses Backbone.sync to persist the state of a model to the server. Can be overridden for custom behavior.

fetchmodel.fetch([options])
Merges the model's state with attributes fetched from the server by delegating to Backbone.sync. Returns a jqXHR. Useful if the model has never been populated with data, or if you'd like to ensure that you have the latest server state. Triggers a "change" event if the server's state differs from the current attributes. fetch accepts success and error callbacks in the options hash, which are both passed (model, response, options) as arguments.

// Poll every 10 seconds to keep the channel model up-to-date.
setInterval(function() {
  channel.fetch();
}, 10000);

savemodel.save([attributes], [options])
Save a model to your database (or alternative persistence layer), by delegating to Backbone.sync. Returns a jqXHR if validation is successful and false otherwise. The attributes hash (as in set) should contain the attributes you'd like to change — keys that aren't mentioned won't be altered — but, a complete representation of the resource will be sent to the server. As with set, you may pass individual keys and values instead of a hash. If the model has a validate method, and validation fails, the model will not be saved. If the model isNew, the save will be a "create" (HTTP POST), if the model already exists on the server, the save will be an "update" (HTTP PUT).

If instead, you'd only like the changed attributes to be sent to the server, call model.save(attrs, {patch: true}). You'll get an HTTP PATCH request to the server with just the passed-in attributes.

Calling save with new attributes will cause a "change" event immediately, a "request" event as the Ajax request begins to go to the server, and a "sync" event after the server has acknowledged the successful change. Pass {wait: true} if you'd like to wait for the server before setting the new attributes on the model.

In the following example, notice how our overridden version of Backbone.sync receives a "create" request the first time the model is saved and an "update" request the second time.

Backbone.sync = function(method, model) {
  alert(method + ": " + JSON.stringify(model));
  model.set('id', 1);
};

var book = new Backbone.Model({
  title: "The Rough Riders",
  author: "Theodore Roosevelt"
});

book.save();

book.save({author: "Teddy"});

save accepts success and error callbacks in the options hash, which will be passed the arguments (model, response, options). If a server-side validation fails, return a non-200 HTTP response code, along with an error response in text or JSON.

book.save("author", "F.D.R.", {error: function(){ ... }});

destroymodel.destroy([options])
Destroys the model on the server by delegating an HTTP DELETE request to Backbone.sync. Returns a jqXHR object, or false if the model isNew. Accepts success and error callbacks in the options hash, which will be passed (model, response, options). Triggers a "destroy" event on the model, which will bubble up through any collections that contain it, a "request" event as it begins the Ajax request to the server, and a "sync" event, after the server has successfully acknowledged the model's deletion. Pass {wait: true} if you'd like to wait for the server to respond before removing the model from the collection.

book.destroy({success: function(model, response) {
  ...
}});

Underscore Methods (9)
Backbone proxies to Underscore.js to provide 9 object functions on Backbone.Model. They aren't all documented here, but you can take a look at the Underscore documentation for the full details…

user.pick('first_name', 'last_name', 'email');

chapters.keys().join(', ');

validatemodel.validate(attributes, options)
This method is left undefined and you're encouraged to override it with any custom validation logic you have that can be performed in JavaScript. If the attributes are valid, don't return anything from validate; if they are invalid return an error of your choosing. It can be as simple as a string error message to be displayed, or a complete error object that describes the error programmatically.

By default save checks validate before setting any attributes but you may also tell set to validate the new attributes by passing {validate: true} as an option. The validate method receives the model attributes as well as any options passed to set or save, if validate returns an error, save does not continue, the model attributes are not modified on the server, an "invalid" event is triggered, and the validationError property is set on the model with the value returned by this method.

var Chapter = Backbone.Model.extend({
  validate: function(attrs, options) {
    if (attrs.end < attrs.start) {
      return "can't end before it starts";
    }
  }
});

var one = new Chapter({
  title : "Chapter One: The Beginning"
});

one.on("invalid", function(model, error) {
  alert(model.get("title") + " " + error);
});

one.save({
  start: 15,
  end:   10
});

"invalid" events are useful for providing coarse-grained error messages at the model or collection level.

validationErrormodel.validationError
The value returned by validate during the last failed validation.

isValidmodel.isValid(options)
Run validate to check the model state.

The validate method receives the model attributes as well as any options passed to isValid, if validate returns an error an "invalid" event is triggered, and the error is set on the model in the validationError property.

var Chapter = Backbone.Model.extend({
  validate: function(attrs, options) {
    if (attrs.end < attrs.start) {
      return "can't end before it starts";
    }
  }
});

var one = new Chapter({
  title : "Chapter One: The Beginning"
});

one.set({
  start: 15,
  end:   10
});

if (!one.isValid()) {
  alert(one.get("title") + " " + one.validationError);
}

urlmodel.url()
Returns the relative URL where the model's resource would be located on the server. If your models are located somewhere else, override this method with the correct logic. Generates URLs of the form: "[collection.url]/[id]" by default, but you may override by specifying an explicit urlRoot if the model's collection shouldn't be taken into account.

Delegates to Collection#url to generate the URL, so make sure that you have it defined, or a urlRoot property, if all models of this class share a common root URL. A model with an id of 101, stored in a Backbone.Collection with a url of "/documents/7/notes", would have this URL: "/documents/7/notes/101"

urlRootmodel.urlRoot or model.urlRoot()
Specify a urlRoot if you're using a model outside of a collection, to enable the default url function to generate URLs based on the model id. "[urlRoot]/id"
Normally, you won't need to define this. Note that urlRoot may also be a function.

var Book = Backbone.Model.extend({urlRoot : '/books'});

var solaris = new Book({id: "1083-lem-solaris"});

alert(solaris.url());

parsemodel.parse(response, options)
parse is called whenever a model's data is returned by the server, in fetch, and save. The function is passed the raw response object, and should return the attributes hash to be set on the model. The default implementation is a no-op, simply passing through the JSON response. Override this if you need to work with a preexisting API, or better namespace your responses.

If you're working with a Rails backend that has a version prior to 3.1, you'll notice that its default to_json implementation includes a model's attributes under a namespace. To disable this behavior for seamless Backbone integration, set:

ActiveRecord::Base.include_root_in_json = false

clonemodel.clone()
Returns a new instance of the model with identical attributes.

isNewmodel.isNew()
Has this model been saved to the server yet? If the model does not yet have an id, it is considered to be new.

hasChangedmodel.hasChanged([attribute])
Has the model changed since its last set? If an attribute is passed, returns true if that specific attribute has changed.

Note that this method, and the following change-related ones, are only useful during the course of a "change" event.

book.on("change", function() {
  if (book.hasChanged("title")) {
    ...
  }
});

changedAttributesmodel.changedAttributes([attributes])
Retrieve a hash of only the model's attributes that have changed since the last set, or false if there are none. Optionally, an external attributes hash can be passed in, returning the attributes in that hash which differ from the model. This can be used to figure out which portions of a view should be updated, or what calls need to be made to sync the changes to the server.

previousmodel.previous(attribute)
During a "change" event, this method can be used to get the previous value of a changed attribute.

var bill = new Backbone.Model({
  name: "Bill Smith"
});

bill.on("change:name", function(model, name) {
  alert("Changed name from " + bill.previous("name") + " to " + name);
});

bill.set({name : "Bill Jones"});

previousAttributesmodel.previousAttributes()
Return a copy of the model's previous attributes. Useful for getting a diff between versions of a model, or getting back to a valid state after an error occurs.

Backbone.Collection

Collections are ordered sets of models. You can bind "change" events to be notified when any model in the collection has been modified, listen for "add" and "remove" events, fetch the collection from the server, and use a full suite of Underscore.js methods.

Any event that is triggered on a model in a collection will also be triggered on the collection directly, for convenience. This allows you to listen for changes to specific attributes in any model in a collection, for example: documents.on("change:selected", ...)

extendBackbone.Collection.extend(properties, [classProperties])
To create a Collection class of your own, extend Backbone.Collection, providing instance properties, as well as optional classProperties to be attached directly to the collection's constructor function.

modelcollection.model([attrs], [options])
Override this property to specify the model class that the collection contains. If defined, you can pass raw attributes objects (and arrays) and options to add, create, and reset, and the attributes will be converted into a model of the proper type using the provided options, if any.

var Library = Backbone.Collection.extend({
  model: Book
});

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

var Library = Backbone.Collection.extend({

  model: function(attrs, options) {
    if (condition) {
      return new PublicDocument(attrs, options);
    } else {
      return new PrivateDocument(attrs, options);
    }
  }

});

modelIdcollection.modelId(attrs)
Override this method to return the value the collection will use to identify a model given its attributes. Useful for combining models from multiple tables with different idAttribute values into a single collection.

By default returns the value of the attributes' idAttribute from the collection's model class or failing that, id. If your collection uses a model factory and those models have an idAttribute other than id you must override this method.

var Library = Backbone.Collection.extend({
  modelId: function(attrs) {
    return attrs.type + attrs.id;
  }
});

var library = new Library([
  {type: 'dvd', id: 1},
  {type: 'vhs', id: 1}
]);

var dvdId = library.get('dvd1').id;
var vhsId = library.get('vhs1').id;
alert('dvd: ' + dvdId + ', vhs: ' + vhsId);

preinitializenew Backbone.Collection([models], [options])
For use with collections as ES classes. If you define a preinitialize method, it will be invoked when the Collection is first created and before any instantiation logic is run for the Collection.

class Library extends Backbone.Collection {
  preinitialize() {
    this.on("add", function() {
      console.log("Add model event got fired!");
    };
  }
}

constructor / initializenew Backbone.Collection([models], [options])
When creating a Collection, you may choose to pass in the initial array of models. The collection's comparator may be included as an option. Passing false as the comparator option will prevent sorting. If you define an initialize function, it will be invoked when the collection is created. There are a couple of options that, if provided, are attached to the collection directly: model and comparator.
Pass null for models to create an empty Collection with options.

var tabs = new TabSet([tab1, tab2, tab3]);
var spaces = new Backbone.Collection(null, {
  model: Space
});

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

toJSONcollection.toJSON([options])
Return an array containing the attributes hash of each model (via toJSON) in the collection. This can be used to serialize and persist the collection as a whole. The name of this method is a bit confusing, because it conforms to JavaScript's JSON API.

var collection = new Backbone.Collection([
  {name: "Tim", age: 5},
  {name: "Ida", age: 26},
  {name: "Rob", age: 55}
]);

alert(JSON.stringify(collection));

synccollection.sync(method, collection, [options])
Uses Backbone.sync to persist the state of a collection to the server. Can be overridden for custom behavior.

Underscore Methods (46)
Backbone proxies to Underscore.js to provide 46 iteration functions on Backbone.Collection. They aren't all documented here, but you can take a look at the Underscore documentation for the full details…

Most methods can take an object or string to support model-attribute-style predicates or a function that receives the model instance as an argument.

books.each(function(book) {
  book.publish();
});

var titles = books.map("title");

var publishedBooks = books.filter({published: true});

var alphabetical = books.sortBy(function(book) {
  return book.author.get("name").toLowerCase();
});

var randomThree = books.sample(3);

addcollection.add(models, [options])
Add a model (or an array of models) to the collection, firing an "add" event for each model, and an "update" event afterwards. If a model property is defined, you may also pass raw attributes objects and options, and have them be vivified as instances of the model using the provided options. Returns the added (or preexisting, if duplicate) models. Pass {at: index} to splice the model into the collection at the specified index. If you're adding models to the collection that are already in the collection, 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 Backbone.Collection;

ships.on("add", function(ship) {
  alert("Ahoy " + ship.get("name") + "!");
});

ships.add([
  {name: "Flying Dutchman"},
  {name: "Black Pearl"}
]);

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

removecollection.remove(models, [options])
Remove a model (or an array of models) from the collection, and return them. Each model can be a Model instance, an id string or a JS object, any value acceptable as the id argument of collection.get. Fires a "remove" event for each model, and a single "update" event afterwards, unless {silent: true} is passed. The model's index before removal is available to listeners as options.index.

resetcollection.reset([models], [options])
Adding and removing models one at a time is all well and good, but sometimes you have 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 on completion, and without triggering any add or remove events on any models. Returns the newly-set models. For convenience, within a "reset" event, the list of any previous models is available as options.previousModels.
Pass null for models to empty your Collection with options.

Here's an example using reset to bootstrap a collection during initial page load, in a Rails application:

<script>
  var accounts = new Backbone.Collection;
  accounts.reset(<%= @accounts.to_json %>);
</script>

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

setcollection.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 yet in the collection it will be added; if the model is already in the collection its attributes will be merged; and if the collection contains any models that aren't present in the list, they'll be removed. All of the appropriate "add", "remove", and "change" events are fired as this happens. Returns the touched models in the collection. If you'd like to customize the behavior, you can disable it with options: {add: false}, {remove: false}, or {merge: false}.

var vanHalen = new Backbone.Collection([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.

getcollection.get(id)
Get a model from a collection, specified by an id, a cid, or by passing in a model.

var book = library.get(110);

atcollection.at(index)
Get a model from a collection, specified by index. Useful if your collection is sorted, and if your collection isn't sorted, at will still retrieve models in insertion order. When passed a negative index, it will retrieve the model from the back of the collection.

pushcollection.push(model, [options])
Add a model at the end of a collection. Takes the same options as add.

popcollection.pop([options])
Remove and return the last model from a collection. Takes the same options as remove.

unshiftcollection.unshift(model, [options])
Add a model at the beginning of a collection. Takes the same options as add.

shiftcollection.shift([options])
Remove and return the first model from a collection. Takes the same options as remove.

slicecollection.slice(begin, end)
Return a shallow copy of this collection's models, using the same options as native Array#slice.

lengthcollection.length
Like an array, a Collection maintains a length property, counting the number of models it contains.

comparatorcollection.comparator
By default there is no comparator for a collection. If you define a comparator, it will be used to sort the collection any time a model is added. A comparator can be defined as a sortBy (pass a function that takes a single argument), as a sort (pass a comparator function that expects two arguments), or as a string indicating the attribute to sort by.

"sortBy" comparator functions take a model and return a numeric or string value by which the model should be ordered relative to others. "sort" comparator functions take two models, and return -1 if the first model should come before the second, 0 if they are of the same rank and 1 if the first model should come after. Note that Backbone depends on the arity of your comparator function to determine between the two styles, so be careful if your comparator function is bound.

Note how even though all of the chapters in this example are added backwards, they come out in the proper order:

var Chapter  = Backbone.Model;
var chapters = new Backbone.Collection;

chapters.comparator = 'page';

chapters.add(new Chapter({page: 9, title: "The End"}));
chapters.add(new Chapter({page: 5, title: "The Middle"}));
chapters.add(new Chapter({page: 1, title: "The Beginning"}));

alert(chapters.pluck('title'));

Collections with a comparator will not automatically re-sort if you later change model attributes, so you may wish to call sort after changing model attributes that would affect the order.

sortcollection.sort([options])
Force a collection to re-sort itself. Note that a collection with a comparator will sort itself automatically whenever a model is added. To disable sorting when adding a model, pass {sort: false} to add. Calling sort triggers a "sort" event on the collection.

pluckcollection.pluck(attribute)
Pluck an attribute from each model in the collection. Equivalent to calling map and returning a single attribute from the iterator.

var stooges = new Backbone.Collection([
  {name: "Curly"},
  {name: "Larry"},
  {name: "Moe"}
]);

var names = stooges.pluck("name");

alert(JSON.stringify(names));

wherecollection.where(attributes)
Return an array of all the models in a collection that match the passed attributes. Useful for simple cases of filter.

var friends = new Backbone.Collection([
  {name: "Athos",      job: "Musketeer"},
  {name: "Porthos",    job: "Musketeer"},
  {name: "Aramis",     job: "Musketeer"},
  {name: "d'Artagnan", job: "Guard"},
]);

var musketeers = friends.where({job: "Musketeer"});

alert(musketeers.length);

findWherecollection.findWhere(attributes)
Just like where, but directly returns only the first model in the collection that matches the passed attributes. If no model matches returns undefined.

urlcollection.url or collection.url()
Set the url property (or function) on a collection to reference its location on the server. Models within the collection will use url to construct URLs of their own.

var Notes = Backbone.Collection.extend({
  url: '/notes'
});

// Or, something more sophisticated:

var Notes = Backbone.Collection.extend({
  url: function() {
    return this.document.url() + '/notes';
  }
});

parsecollection.parse(response, options)
parse is called by Backbone whenever a collection's models are returned by the server, in fetch. The function is passed the raw response object, and should return the array of model attributes to be added to the collection. The default implementation is a no-op, simply passing through the JSON response. Override this if you need to work with a preexisting API, or better namespace your responses.

var Tweets = Backbone.Collection.extend({
  // The Twitter Search API returns tweets under "results".
  parse: function(response) {
    return response.results;
  }
});

clonecollection.clone()
Returns a new instance of the collection with an identical list of models.

fetchcollection.fetch([options])
Fetch the default set of models for this collection from the server, setting them on the collection when they arrive. The options hash takes success and error callbacks which will both be passed (collection, response, options) as arguments. When the model data returns from the server, it uses set to (intelligently) merge the fetched models, unless you pass {reset: true}, in which case the collection will be (efficiently) reset. Delegates to Backbone.sync under the covers for custom persistence strategies and returns a jqXHR. The server handler for fetch requests should return a JSON array of models.

Backbone.sync = function(method, model) {
  alert(method + ": " + model.url);
};

var accounts = new Backbone.Collection;
accounts.url = '/accounts';

accounts.fetch();

The behavior of fetch can be customized by using the available set options. For example, to fetch a collection, getting an "add" event for every new model, and a "change" event for every changed existing model, without removing anything: collection.fetch({remove: false})

jQuery.ajax options can also be passed directly as fetch options, so to fetch a specific page of a paginated collection: Documents.fetch({data: {page: 3}})

Note that fetch should not be used to populate collections on page load — all models needed at load time should already be bootstrapped in to place. fetch is intended for lazily-loading models for interfaces that are not needed immediately: for example, documents with collections of notes that may be toggled open and closed.

createcollection.create(attributes, [options])
Convenience to create a new instance of a model within a collection. Equivalent to instantiating a model with a hash of attributes, saving the model to the server, and adding the model to the set after being successfully created. Returns the new model. If client-side validation failed, the model will be unsaved, with validation errors. In order for this to work, you should set the model property of the collection. The create method can accept either an attributes hash and options to be passed down during model instantiation or an existing, unsaved model object.

Creating a model will cause an immediate "add" event to be triggered on the collection, a "request" event as the new model is sent to the server, as well as a "sync" event, once the server has responded with the successful creation of the model. Pass {wait: true} if you'd like to wait for the server before adding the new model to the collection.

var Library = Backbone.Collection.extend({
  model: Book
});

var nypl = new Library;

var othello = nypl.create({
  title: "Othello",
  author: "William Shakespeare"
});

mixinBackbone.Collection.mixin(properties)
mixin provides a way to enhance the base Backbone.Collection and any collections which extend it. This can be used to add generic methods (e.g. additional Underscore Methods).

Backbone.Collection.mixin({
  sum: function(models, iteratee) {
    return _.reduce(models, function(s, m) {
      return s + iteratee(m);
    }, 0);
  }
});

var cart = new Backbone.Collection([
  {price: 16, name: 'monopoly'},
  {price: 5, name: 'deck of cards'},
  {price: 20, name: 'chess'}
]);

var cost = cart.sum('price');

Backbone.Router

Web applications often provide linkable, bookmarkable, shareable URLs for important locations in the app. Until recently, hash fragments (#page) were used to provide these permalinks, but with the arrival of the History API, it's now possible to use standard URLs (/page). Backbone.Router provides methods for routing client-side pages, and connecting them to actions and events. For browsers which don't yet support the History API, the Router handles graceful fallback and transparent translation to the fragment version of the URL.

During page load, after your application has finished creating all of its routers, be sure to call Backbone.history.start() or Backbone.history.start({pushState: true}) to route the initial URL.

extendBackbone.Router.extend(properties, [classProperties])
Get started by creating a custom router class. Define action functions that are triggered when certain URL fragments are matched, and provide a routes hash that pairs routes to actions. Note that you'll want to avoid using a leading slash in your route definitions:

var Workspace = Backbone.Router.extend({

  routes: {
    "help":                 "help",    // #help
    "search/:query":        "search",  // #search/kiwis
    "search/:query/p:page": "search"   // #search/kiwis/p7
  },

  help: function() {
    ...
  },

  search: function(query, page) {
    ...
  }

});

routesrouter.routes
The routes hash maps URLs with parameters to functions on your router (or just direct function definitions, if you prefer), similar to the View's events hash. Routes can contain parameter parts, :param, which match a single URL component between slashes; and splat parts *splat, which can match any number of URL components. Part of a route can be made optional by surrounding it in parentheses (/:optional).

For example, a route of "search/:query/p:page" will match a fragment of #search/obama/p2, passing "obama" and "2" to the action as positional arguments.

A route of "file/*path" will match #file/folder/file.txt, passing "folder/file.txt" to the action.

A route of "docs/:section(/:subsection)" will match #docs/faq and #docs/faq/installing, passing "faq" to the action in the first case, and passing "faq" and "installing" to the action in the second.

A nested optional route of "docs(/:section)(/:subsection)" will match #docs, #docs/faq, and #docs/faq/installing, passing "faq" to the action in the second case, and passing "faq" and "installing" to the action in the third.

Trailing slashes are treated as part of the URL, and (correctly) treated as a unique route when accessed. docs and docs/ will fire different callbacks. If you can't avoid generating both types of URLs, you can define a "docs(/)" matcher to capture both cases.

When the visitor presses the back button, or enters a URL, and a particular route is matched, the name of the action will be fired as an event, so that other objects can listen to the router, and be notified. In the following example, visiting #help/uploading will fire a route:help event from the router.

routes: {
  "help/:page":         "help",
  "download/*path":     "download",
  "folder/:name":       "openFolder",
  "folder/:name-:mode": "openFolder"
}

router.on("route:help", function(page) {
  ...
});

preinitializenew Backbone.Router([options])
For use with routers as ES classes. If you define a preinitialize method, it will be invoked when the Router is first created and before any instantiation logic is run for the Router.

class Router extends Backbone.Router {
  preinitialize() {
    // Override execute method
    this.execute = function(callback, args, name) {
      if (!loggedIn) {
        goToLogin();
        return false;
      }
      args.push(parseQueryString(args.pop()));
      if (callback) callback.apply(this, args);
    }
  }
}

constructor / initializenew Router([options])
When creating a new router, you may pass its routes hash directly as an option, if you choose. All options will also be passed to your initialize function, if defined.

routerouter.route(route, name, [callback])
Manually create a route for the router, The route argument may be a routing string or regular expression. Each matching capture from the route or regular expression will be passed as an argument to the callback. The name argument will be triggered as a "route:name" event whenever the route is matched. If the callback argument is omitted router[name] will be used instead. Routes added later may override previously declared routes.

initialize: function(options) {

  // Matches #page/10, passing "10"
  this.route("page/:number", "page", function(number){ ... });

  // Matches /117-a/b/c/open, passing "117-a/b/c" to this.open
  this.route(/^(.*?)\/open$/, "open");

},

open: function(id) { ... }

navigaterouter.navigate(fragment, [options])
Whenever you reach a point in your application that you'd like to save as a URL, call navigate in order to update the URL. If you also wish to call the route function, set the trigger option to true. To update the URL without creating an entry in the browser's history, set the replace option to true.

openPage: function(pageNumber) {
  this.document.pages.at(pageNumber).open();
  this.navigate("page/" + pageNumber);
}

# Or ...

app.navigate("help/troubleshooting", {trigger: true});

# Or ...

app.navigate("help/troubleshooting", {trigger: true, replace: true});

executerouter.execute(callback, args, name)
This method is called internally within the router, whenever a route matches and its corresponding callback is about to be executed. Return false from execute to cancel the current transition. Override it to perform custom parsing or wrapping of your routes, for example, to parse query strings before handing them to your route callback, like so:

var Router = Backbone.Router.extend({
  execute: function(callback, args, name) {
    if (!loggedIn) {
      goToLogin();
      return false;
    }
    args.push(parseQueryString(args.pop()));
    if (callback) callback.apply(this, args);
  }
});

Backbone.history

History serves as a global router (per frame) to handle hashchange events or pushState, match the appropriate route, and trigger callbacks. You shouldn't ever have to create one of these yourself since Backbone.history already contains one.

pushState support exists on a purely opt-in basis in Backbone. Older browsers that don't support pushState will continue to use hash-based URL fragments, and if a hash URL is visited by a pushState-capable browser, it will be transparently upgraded to the true URL. Note that using real URLs requires your web server to be able to correctly render those pages, so back-end changes are required as well. For example, if you have a route of /documents/100, your web server must be able to serve that page, if the browser visits that URL directly. For full search-engine crawlability, it's best to have the server generate the complete HTML for the page ... but if it's a web application, just rendering the same content you would have for the root URL, and filling in the rest with Backbone Views and JavaScript works fine.

startBackbone.history.start([options])
When all of your Routers have been created, and all of the routes are set up properly, call Backbone.history.start() to begin monitoring hashchange events, and dispatching routes. Subsequent calls to Backbone.history.start() will throw an error, and Backbone.History.started is a boolean value indicating whether it has already been called.

To indicate that you'd like to use HTML5 pushState support in your application, use Backbone.history.start({pushState: true}). If you'd like to use pushState, but have browsers that don't support it natively use full page refreshes instead, you can add {hashChange: false} to the options.

If your application is not being served from the root url / of your domain, be sure to tell History where the root really is, as an option: Backbone.history.start({pushState: true, root: "/public/search/"})

When called, if a route succeeds with a match for the current URL, Backbone.history.start() returns true. If no defined route matches the current URL, it returns false.

If the server has already rendered the entire page, and you don't want the initial route to trigger when starting History, pass silent: true.

Because hash-based history in Internet Explorer relies on an <iframe>, be sure to call start() only after the DOM is ready.

$(function(){
  new WorkspaceRouter();
  new HelpPaneRouter();
  Backbone.history.start({pushState: true});
});

Backbone.sync

Backbone.sync is the function that Backbone calls every time it attempts to read or save a model to the server. By default, it uses jQuery.ajax to make a RESTful JSON request and returns a jqXHR. You can override it in order to use a different persistence strategy, such as WebSockets, XML transport, or Local Storage.

The method signature of Backbone.sync is sync(method, model, [options])

method – the CRUD method ("create", "read", "update", or "delete")
model – the model to be saved (or collection to be read)
options – success and error callbacks, and all other jQuery request options

With the default implementation, when Backbone.sync sends up a request to save a model, its attributes will be passed, serialized as JSON, and sent in the HTTP body with content-type application/json. When returning a JSON response, send down the attributes of the model that have been changed by the server, and need to be updated on the client. When responding to a "read" request from a collection (Collection#fetch), send down an array of model attribute objects.

Whenever a model or collection begins a sync with the server, a "request" event is emitted. If the request completes successfully you'll get a "sync" event, and an "error" event if not.

The sync function may be overridden globally as Backbone.sync, or at a finer-grained level, by adding a sync function to a Backbone collection or to an individual model.

The default sync handler maps CRUD to REST like so:

create → POST /collection
read → GET /collection[/id]
update → PUT /collection/id
patch → PATCH /collection/id
delete → DELETE /collection/id

As an example, a Rails 4 handler responding to an "update" call from Backbone might look like this:

def update
  account = Account.find params[:id]
  permitted = params.require(:account).permit(:name, :otherparam)
  account.update_attributes permitted
  render :json => account
end

One more tip for integrating Rails versions prior to 3.1 is to disable the default namespacing for to_json calls on models by setting ActiveRecord::Base.include_root_in_json = false

ajaxBackbone.ajax = function(request) { ... };
If you want to use a custom AJAX function, or your endpoint doesn't support the jQuery.ajax API and you need to tweak things, you can do so by setting Backbone.ajax.

emulateHTTPBackbone.emulateHTTP = true
If you want to work with a legacy web server that doesn't support Backbone's default REST/HTTP approach, you may choose to turn on Backbone.emulateHTTP. Setting this option will fake PUT, PATCH and DELETE requests with a HTTP POST, setting the X-HTTP-Method-Override header with the true method. If emulateJSON is also on, the true method will be passed as an additional _method parameter.

Backbone.emulateHTTP = true;

model.save();  // POST to "/collection/id", with "_method=PUT" + header.

emulateJSONBackbone.emulateJSON = true
If you're working with a legacy web server that can't handle requests encoded as application/json, setting Backbone.emulateJSON = true; will cause the JSON to be serialized under a model parameter, and the request to be made with a application/x-www-form-urlencoded MIME type, as if from an HTML form.

Backbone.View

Backbone views are almost more convention than they are code — they don't determine anything about your HTML or CSS for you, and can be used with any JavaScript templating library. The general idea is to organize your interface into logical views, backed by models, each of which can be updated independently when the model changes, without having to redraw the page. Instead of digging into a JSON object, looking up an element in the DOM, and updating the HTML by hand, you can bind your view's render function to the model's "change" event — and now everywhere that model data is displayed in the UI, it is always immediately up to date.

extendBackbone.View.extend(properties, [classProperties])
Get started with views by creating a custom view class. You'll want to override the render function, specify your declarative events, and perhaps the tagName, className, or id of the View's root element.

var DocumentRow = Backbone.View.extend({

  tagName: "li",

  className: "document-row",

  events: {
    "click .icon":          "open",
    "click .button.edit":   "openEditDialog",
    "click .button.delete": "destroy"
  },

  initialize: function() {
    this.listenTo(this.model, "change", this.render);
  },

  render: function() {
    ...
  }

});

Properties like tagName, id, className, el, and events may also be defined as a function, if you want to wait to define them until runtime.

preinitializenew View([options])
For use with views as ES classes. If you define a preinitialize method, it will be invoked when the view is first created, before any instantiation logic is run.

class Document extends Backbone.View {
  preinitialize({autoRender}) {
    this.autoRender = autoRender;
  }

  initialize() {
    if (this.autoRender) {
      this.listenTo(this.model, "change", this.render);
    }
  }
}

constructor / initializenew View([options])
There are several special options that, if passed, will be attached directly to the view: model, collection, el, id, className, tagName, attributes and events. If the view defines an initialize function, it will be called when the view is first created. If you'd like to create a view that references an element already in the DOM, pass in the element as an option: new View({el: existingElement})

var doc = documents.first();

new DocumentRow({
  model: doc,
  id: "document-row-" + doc.id
});

elview.el
All views have a DOM element at all times (the el property), whether they've already been inserted into the page or not. In this fashion, views can be rendered at any time, and inserted into the DOM all at once, in order to get high-performance UI rendering with as few reflows and repaints as possible.

this.el can be resolved from a DOM selector string or an Element; otherwise it will be created from the view's tagName, className, id and attributes properties. If none are set, this.el is an empty div, which is often just fine. An el reference may also be passed in to the view's constructor.

var ItemView = Backbone.View.extend({
  tagName: 'li'
});

var BodyView = Backbone.View.extend({
  el: 'body'
});

var item = new ItemView();
var body = new BodyView();

alert(item.el + ' ' + body.el);

$elview.$el
A cached jQuery object for the view's element. A handy reference instead of re-wrapping the DOM element all the time.

view.$el.show();

listView.$el.append(itemView.el);

setElementview.setElement(element)
If you'd like to apply a Backbone view to a different DOM element, use setElement, which will also create the cached $el reference and move the view's delegated events from the old element to the new one.

attributesview.attributes
A hash of attributes that will be set as HTML DOM element attributes on the view's el (id, class, data-properties, etc.), or a function that returns such a hash.

$ (jQuery)view.$(selector)
If jQuery is included on the page, each view has a $ function that runs queries scoped within the view's element. If you use this scoped jQuery function, you don't have to use model ids as part of your query to pull out specific elements in a list, and can rely much more on HTML class attributes. It's equivalent to running: view.$el.find(selector)

ui.Chapter = Backbone.View.extend({
  serialize : function() {
    return {
      title: this.$(".title").text(),
      start: this.$(".start-page").text(),
      end:   this.$(".end-page").text()
    };
  }
});

templateview.template([data])
While templating for a view isn't a function provided directly by Backbone, it's often a nice convention to define a template function on your views. In this way, when rendering your view, you have convenient access to instance data. For example, using Underscore templates:

var LibraryView = Backbone.View.extend({
  template: _.template(...)
});

renderview.render()
The default implementation of render is a no-op. Override this function with your code that renders the view template from model data, and updates this.el with the new HTML. A good convention is to return this at the end of render to enable chained calls.

var Bookmark = Backbone.View.extend({
  template: _.template(...),
  render: function() {
    this.$el.html(this.template(this.model.attributes));
    return this;
  }
});

Backbone is agnostic with respect to your preferred method of HTML templating. Your render function could even munge together an HTML string, or use document.createElement to generate a DOM tree. However, we suggest choosing a nice JavaScript templating library. Mustache.js, Haml-js, and Eco are all fine alternatives. Because Underscore.js is already on the page, _.template is available, and is an excellent choice if you prefer simple interpolated-JavaScript style templates.

Whatever templating strategy you end up with, it's nice if you never have to put strings of HTML in your JavaScript. At DocumentCloud, we use Jammit in order to package up JavaScript templates stored in /app/views as part of our main core.js asset package.

removeview.remove()
Removes a view and its el from the DOM, and calls stopListening to remove any bound events that the view has listenTo'd.

eventsview.events or view.events()
The events hash (or method) can be used to specify a set of DOM events that will be bound to methods on your View through delegateEvents.

Backbone will automatically attach the event listeners at instantiation time, right before invoking initialize.

var ENTER_KEY = 13;
var InputView = Backbone.View.extend({

  tagName: 'input',

  events: {
    "keydown" : "keyAction",
  },

  render: function() { ... },

  keyAction: function(e) {
    if (e.which === ENTER_KEY) {
      this.collection.add({text: this.$el.val()});
    }
  }
});

delegateEventsdelegateEvents([events])
Uses jQuery's on function to provide declarative callbacks for DOM events within a view. If an events hash is not passed directly, uses this.events as the source. Events are written in the format {"event selector": "callback"}. The callback may be either the name of a method on the view, or a direct function body. Omitting the selector causes the event to be bound to the view's root element (this.el). By default, delegateEvents is called within the View's constructor for you, so if you have a simple events hash, all of your DOM events will always already be connected, and you will never have to call this function yourself.

The events property may also be defined as a function that returns an events hash, to make it easier to programmatically define your events, as well as inherit them from parent views.

Using delegateEvents provides a number of advantages over manually using jQuery to bind events to child elements during render. All attached callbacks are bound to the view before being handed off to jQuery, so when the callbacks are invoked, this continues to refer to the view object. When delegateEvents is run again, perhaps with a different events hash, all callbacks are removed and delegated afresh — useful for views which need to behave differently when in different modes.

A single-event version of delegateEvents is available as delegate. In fact, delegateEvents is simply a multi-event wrapper around delegate. A counterpart to undelegateEvents is available as undelegate.

A view that displays a document in a search result might look something like this:

var DocumentView = Backbone.View.extend({

  events: {
    "dblclick"                : "open",
    "click .icon.doc"         : "select",
    "contextmenu .icon.doc"   : "showMenu",
    "click .show_notes"       : "toggleNotes",
    "click .title .lock"      : "editAccessLevel",
    "mouseover .title .date"  : "showTooltip"
  },

  render: function() {
    this.$el.html(this.template(this.model.attributes));
    return this;
  },

  open: function() {
    window.open(this.model.get("viewer_url"));
  },

  select: function() {
    this.model.set({selected: true});
  },

  ...

});

undelegateEventsundelegateEvents()
Removes all of the view's delegated events. Useful if you want to disable or remove a view from the DOM temporarily.

Utility

Backbone.noConflictvar backbone = Backbone.noConflict();
Returns the Backbone object back to its original value. You can use the return value of Backbone.noConflict() to keep a local reference to Backbone. Useful for embedding Backbone on third-party websites, where you don't want to clobber the existing Backbone.

var localBackbone = Backbone.noConflict();
var model = localBackbone.Model.extend(...);

Backbone.$Backbone.$ = $;
If you have multiple copies of jQuery on the page, or simply want to tell Backbone to use a particular object as its DOM / Ajax library, this is the property for you.

Backbone.$ = require('jquery');