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Backbone.js

Backbone.js gives structure to web applications by providing models with key-value binding and custom events, collections with a rich API of enumerable functions,views with declarative event handling, and connects it all to your existing API over a RESTful JSON interface.

The project is hosted on GitHub, and the annotated source code is available, as well as an online test suite, an example application, a list of tutorials and a long list of real-world projects that use Backbone. Backbone is available for use under the MIT software license.

You can report bugs and discuss features on the GitHub issues page, on Freenode IRC in the #documentcloud channel, post questions to the Google Group, add pages to the wiki or send tweets to @documentcloud.

Backbone is an open-source component of DocumentCloud.

Downloads & Dependencies (Right-click, and use "Save As")

Development Version (1.0.0) 58kb, Full source, tons of comments
Production Version (1.0.0) 6.3kb, Packed and gzipped
(Source Map)
Edge Version (master) Unreleased, use at your own risk

Backbone's only hard dependency is Underscore.js ( >= 1.4.3). For RESTful persistence, history support via Backbone.Router and DOM manipulation with Backbone.View, include json2.js, and either jQuery ( >= 1.7.0) or Zepto.

Introduction

When working on a web application that involves a lot of JavaScript, one of the first things you learn is to stop tying your data to the DOM. It's all too easy to create JavaScript applications that end up as tangled piles of jQuery selectors and callbacks, all trying frantically to keep data in sync between the HTML UI, your JavaScript logic, and the database on your server. For rich client-side applications, a more structured approach is often helpful.

With Backbone, you represent your data as Models, which can be created, validated, destroyed, and saved to the server. Whenever a UI action causes an attribute of a model to change, the model triggers a "change" event; all the Views that display the model's state can be notified of the change, so that they are able to respond accordingly, re-rendering themselves with the new information. In a finished Backbone app, you don't have to write the glue code that looks into the DOM to find an element with a specific id, and update the HTML manually — when the model changes, the views simply update themselves.

If you're new here, and aren't yet quite sure what Backbone is for, start by browsing thelist of Backbone-based projects.

Many of the examples that follow are runnable. Click the play button to execute them.

Upgrading to 1.0

Backbone 1.0 should be a fairly painless upgrade from the 0.9 series. If you're upgrading from an older version, be sure to check out the change log. In brief, a few of the larger breaking changes are:

  • If you want to smartly update the contents of a Collection, adding new models, removing missing ones, and merging those already present, you now call set (previously named "update"), a similar operation to calling set on a Model. This is now the default when you callfetch on a collection. To get the old behavior, pass {reset: true}.
  • If you have characters in your URL segments that require URL encoding, Backbone will now decode them for you (normalizing the behavior cross-browser) before your route handlers receive them as arguments.
  • In 0.9.x, Backbone events gained two new methods: listenTo and stopListening, which make it easier to create Views that have all of their observers unbound when you want to remove the view.
  • Model validation is now only enforced by default in save — not in set unless the{validate:true} option is passed. Model validation now fires an "invalid" event instead of "error".

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 eventis 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", ...);

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

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:title": titleView.update,
  "change:author": authorPane.update,
  "destroy": bookView.remove
});

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 only fire once before being removed. Handy for saying "the next time that X happens, do this".

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), is that listenTo allows theobject to keep track of the events, and they can be removed all at once later on.

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 only fire 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. TheBackbone 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.
  • "reset" (collection, options) — when the collection's entire contents have been replaced.
  • "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, xhr, options) — when a model (or collection) has started a request to the server.
  • "sync" (model, resp, options) — when a model (or collection) has been successfully synced with the server.
  • "error" (model, xhr, options) — when a model's save call fails on the server.
  • "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" (router, route, params) — Fired by history (or router) when any route has been matched.
  • "all" — this special event fires for any triggered event, passing the event name as the first argument.

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, orsave, 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);
    ...
  }
});

constructor / initializenew Model([attributes], [options]) 
When creating an instance of a model, you can pass in the initial values of theattributes, 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 collectionproperty 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 otherwise added automatically when you first add a model to a collection.

{url: "..."} and/or {urlRoot: "..."} options may be passed when creating a new model that needs to have a custom one-off URL endpoint.

If {parse: true} is passed as an option, the attributes will first be converted byparse 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: ""
});

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. 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 the last "change" event was triggered. Please do not update changeddirectly 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() 
Return a 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]) 
Resets the model's state from the server by delegating to Backbone.sync. Returns ajqXHR. Useful if the model has never been populated with data, or if you'd like to ensure that you have the latest server state. A "change" event will be triggered if the server's state differs from the current attributes. Accepts success and errorcallbacks 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 toBackbone.sync. Returns a jqXHR if validation is successful and false otherwise. Theattributes 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, callmodel.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.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 are passed(model, response, options) and (model, xhr, options) as arguments, respectively. 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 toBackbone.sync. Returns a jqXHR object, or false if the model isNew. Acceptssuccess and error callbacks in the options hash, which are passed (model, response, options) and (model, xhr, options) as arguments, respectively. 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 (6) 
Backbone proxies to Underscore.js to provide 6 object functions onBackbone.Model. They aren't all documented here, but you can take a look at the Underscore documentation for the full details…

  • keys
  • values
  • pairs
  • invert
  • pick
  • omit
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 your custom validation logic, if you have any that can be performed in JavaScript. By defaultvalidate is called before save, but can also be called before set if {validate:true}is passed. The validate method is passed the model attributes, as well as the options from set or save. 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. If validate returns an error, save will not continue, and the model attributes will not be modified on the server. Failed validations trigger an "invalid"event, and set the validationError property 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 
Run validate to check the model state.

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. You can also pass in the model's url as an option when instantiating it.

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

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

A collection can also contain polymorphic models by overriding this property with a function 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);
    }
  }

});

constructor / initializenew 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 several options that, if provided, are attached to the collection directly: url, model and comparator.

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

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() 
Return an array containing the attributes hash of each model 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 (28) 
Backbone proxies to Underscore.js to provide 28 iteration functions onBackbone.Collection. They aren't all documented here, but you can take a look at the Underscore documentation for the full details…

  • forEach (each)
  • map (collect)
  • reduce (foldl, inject)
  • reduceRight (foldr)
  • find (detect)
  • filter (select)
  • reject
  • every (all)
  • some (any)
  • contains (include)
  • invoke
  • max
  • min
  • sortBy
  • groupBy
  • sortedIndex
  • shuffle
  • toArray
  • size
  • first (head, take)
  • initial
  • rest (tail)
  • last
  • without
  • indexOf
  • lastIndexOf
  • isEmpty
  • chain
books.each(function(book) {
  book.publish();
});

var titles = books.map(function(book) {
  return book.get("title");
});

var publishedBooks = books.filter(function(book) {
  return book.get("published") === true;
});

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

addcollection.add(models, [options]) 
Add a model (or an array of models) to the collection, firing an "add" event. If a modelproperty is defined, you may also pass raw attributes objects, and have them be vivified as instances of the model. 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. Fires a "remove" event, which you can use silent to suppress. 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. Usereset 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.

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

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. If you'd like to customize the behavior, you can disable it with options: {add: false}, {remove: false}, or{merge: false}.

var vanHalen = new 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.

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 asremove.

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 asremove.

slicecollection.slice(begin, end) 
Return a shallow copy of this collection's models, using the same options as nativeArray#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 maintain the collection in sorted order. This means that as models are added, they are inserted at the correct index in collection.models. 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 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 = function(chapter) {
  return chapter.get("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. 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 disable sorting when adding a model, pass {sort: false} to add. Callingsort 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.

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 createmethod can accept either an attributes hash 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"
});

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 actions 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.

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

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/uploadingwill 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) {
  ...
});

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.

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, callnavigate in order to update the URL. If you wish to also call the route function, set thetrigger 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});

Backbone.history

History serves as a global router (per frame) to handle hashchange events orpushState, 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.

To indicate that you'd like to use HTML5 pushState support in your application, useBackbone.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