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Backbone.js

Backbone.js (1.6.0)

- » GitHub Repository
- » Annotated Source

Getting Started

- \- Introduction
- – Models and Views
- – Collections
- – API Integration
- – Rendering
- – Routing

Events

- – on
- – off
- – trigger
- – once
- – listenTo
- – stopListening
- – listenToOnce
- \- **Catalog of Built-in Events**

Model

- – extend
- – preinitialize
- – constructor / initialize
- – get
- – set
- – escape
- – has
- – unset
- – clear
- – id
- – idAttribute
- – cid
- – cidPrefix
- – attributes
- – changed
- – defaults
- – toJSON
- – sync
- – fetch
- – save
- – destroy
- – **Underscore Methods (9)**
- – validate
- – validationError
- – isValid
- – url
- – urlRoot
- – parse
- – clone
- – isNew
- – hasChanged
- – changedAttributes
- – previous
- – previousAttributes

Collection

- – extend
- – model
- – modelId
- – preinitialize
- – constructor / initialize
- – models
- – toJSON
- – sync
- – **Underscore Methods (46)**
- – add
- – remove
- – reset
- – set
- – get
- – at
- – push
- – pop
- – unshift
- – shift
- – slice
- – length
- – comparator
- – sort
- – pluck
- – where
- – findWhere
- – url
- – parse
- – clone
- – fetch
- – create
- – mixin

Router

- – extend
- – routes
- – preinitialize
- – constructor / initialize
- – route
- – navigate
- – execute

History

- – start

Sync

- – Backbone.sync
- – Backbone.ajax
- – Backbone.emulateHTTP
- – Backbone.emulateJSON

View

- – extend
- – preinitialize
- – constructor / initialize
- – el
- – $el
- – setElement
- – attributes
- – $ (jQuery)
- – template
- – render
- – remove
- – events
- – delegateEvents
- – undelegateEvents

Utility

- – Backbone.noConflict
- – Backbone.$
- – debugInfo

F.A.Q.

- – Why Backbone?
- – More Than One Way To Do It
- – Nested Models & Collections
- – Loading Bootstrapped Models
- – Extending Backbone
- – Traditional MVC
- – Binding "this"
- – Working with Rails

Examples

- – Todos
- – DocumentCloud
- – USA Today
- – Rdio
- – Hulu
- – Quartz
- – Earth
- – Vox
- – Gawker Media
- – Flow
- – Gilt Groupe
- – Enigma
- – NewsBlur
- – WordPress.com
- – Foursquare
- – Bitbucket
- – Disqus
- – Delicious
- – Khan Academy
- – IRCCloud
- – Pitchfork
- – Spin
- – ZocDoc
- – Walmart Mobile
- – Groupon Now!
- – Basecamp
- – Slavery Footprint
- – Stripe
- – Airbnb
- – SoundCloud Mobile
- \- Art.sy
- – Pandora
- – Inkling
- – Code School
- – CloudApp
- – SeatGeek
- – Easel
- \- Jolicloud
- – Salon.io
- – TileMill
- – Blossom
- – Trello
- – Tzigla

Change Log

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, or add pages to the wiki.

*Backbone is an open-source component of DocumentCloud.*

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

Development Version (1.6.0)

*72kb, Full source, tons of comments*

Production Version (1.6.0)

*7.9kb, Packed and gzipped*
(Source Map)

Edge Version (master)

*Unreleased, use at your own risk*

Backbone's only hard dependency is Underscore.js ( >= 1.8.3). For RESTful persistence and DOM manipulation with Backbone.View, include **jQuery** ( >= 1.11.0). *(Mimics of the Underscore and jQuery APIs, such as Lodash and Zepto, will also tend to work, with varying degrees of compatibility.)*

## Getting Started

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.

Philosophically, Backbone is an attempt to discover the minimal set of data-structuring (models and collections) and user interface (views and URLs) primitives that are generally useful when building web applications with JavaScript. In an ecosystem where overarching, decides-everything-for-you frameworks are commonplace, and many libraries require your site to be reorganized to suit their look, feel, and default behavior — Backbone should continue to be a tool that gives you the *freedom* to design the full experience of your web application.

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

Many of the code examples in this documentation are runnable, because Backbone is included on this page. Click the *play* button to execute them.

## Models and Views

The single most important thing that Backbone can help you with is keeping your business logic separate from your user interface. When the two are entangled, change is hard; when logic doesn't depend on UI, your interface becomes easier to work with.

**Model**

- Orchestrates data and business logic.
- Loads and saves data from the server.
- Emits events when data changes.

**View**

- Listens for changes and renders UI.
- Handles user input and interactivity.
- Sends captured input to the model.

A **Model** manages an internal table of data attributes, and triggers "change" events when any of its data is modified. Models handle syncing data with a persistence layer — usually a REST API with a backing database. Design your models as the atomic reusable objects containing all of the helpful functions for manipulating their particular bit of data. Models should be able to be passed around throughout your app, and used anywhere that bit of data is needed.

A **View** is an atomic chunk of user interface. It often renders the data from a specific model, or number of models — but views can also be data-less chunks of UI that stand alone. Models should be generally unaware of views. Instead, views listen to the model "change" events, and react or re-render themselves appropriately.

## Collections

A **Collection** helps you deal with a group of related models, handling the loading and saving of new models to the server and providing helper functions for performing aggregations or computations against a list of models. Aside from their own events, collections also proxy through all of the events that occur to models within them, allowing you to listen in one place for any change that might happen to any model in the collection.

## API Integration

Backbone is pre-configured to sync with a RESTful API. Simply create a new Collection with the url of your resource endpoint:

var Books = Backbone.Collection.extend({
url: '/books'
});

The **Collection** and **Model** components together form a direct mapping of REST resources using the following methods:

GET  /books/ .... collection.fetch();
POST /books/ .... collection.create();
GET  /books/1 ... model.fetch();
PUT  /books/1 ... model.save();
DEL  /books/1 ... model.destroy();

When fetching raw JSON data from an API, a **Collection** will automatically populate itself with data formatted as an array, while a **Model** will automatically populate itself with data formatted as an object:

\[{"id": 1}\] ..... populates a Collection with one model.
{"id": 1} ....... populates a Model with one attribute.

However, it's fairly common to encounter APIs that return data in a different format than what Backbone expects. For example, consider fetching a **Collection** from an API that returns the real data array wrapped in metadata:

{
"page": 1,
"limit": 10,
"total": 2,
"books": \[
{"id": 1, "title": "Pride and Prejudice"},
{"id": 4, "title": "The Great Gatsby"}
\]
}

In the above example data, a **Collection** should populate using the "books" array rather than the root object structure. This difference is easily reconciled using a parse method that returns (or transforms) the desired portion of API data:

var Books = Backbone.Collection.extend({
url: '/books',
parse: function(data) {
return data.books;
}
});

## View Rendering

Each **View** manages the rendering and user interaction within its own DOM element. If you're strict about not allowing views to reach outside of themselves, it helps keep your interface flexible — allowing views to be rendered in isolation in any place where they might be needed.

Backbone remains unopinionated about the process used to render **View** objects and their subviews into UI: you define how your models get translated into HTML (or SVG, or Canvas, or something even more exotic). It could be as prosaic as a simple Underscore template, or as fancy as the React virtual DOM. Some basic approaches to rendering views can be found in the Backbone primer.

## Routing with URLs

In rich web applications, we still want to provide linkable, bookmarkable, and shareable URLs to meaningful locations within an app. Use the **Router** to update the browser URL whenever the user reaches a new "place" in your app that they might want to bookmark or share. Conversely, the **Router** detects changes to the URL — say, pressing the "Back" button — and can tell your application exactly where you are now.

## 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)

**on**`object.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).

**off**`object.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.

**trigger**`object.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.

**once**`object.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

**listenTo**`object.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);

**stopListening**`object.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);

**listenToOnce**`object.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.
- **"changeId"** (model, previousId, options) — when the model's id has been updated.
- **"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.
- **"notfound"** () — Fired by history when *no* route could be 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();

**extend**`Backbone.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);
...
}
});

**preinitialize**`new 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 / initialize**`new 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.

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

**set**`model.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");

**escape**`model.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'));

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

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

**unset**`model.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.

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

**id**`model.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.

**idAttribute**`model.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. If you set idAttribute, you may also want to override cidPrefix.

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

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

**cid**`model.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.

**cidPrefix**`model.cidPrefix`
If your model has an id that is anything other than an integer or a UUID, there is the possibility that it might collide with its cid. To prevent this, you can override the prefix that cids start with.

// If both lengths are 2, refresh the page before running this example.
var clashy = new Backbone.Collection(\[
{id: 'c2'},
{id: 'c1'},
\]);
alert('clashy length: ' + clashy.length);

var ClashFree = Backbone.Model.extend({cidPrefix: 'm'});
var clashless = new Backbone.Collection(\[
{id: 'c3'},
{id: 'c2'},
\], {model: ClashFree});
alert('clashless length: ' + clashless.length);

**attributes**`model.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.

**changed**`model.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.

**defaults**`model.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.

If you set a value for the model’s idAttribute, you should define the defaults as a function that returns a different, universally unique id on every invocation. Not doing so would likely prevent an instance of Backbone.Collection from correctly identifying model hashes and is almost certainly a mistake, unless you never add instances of the model class to a collection.

**toJSON**`model.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));

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

**fetch**`model.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);

**save**`model.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(){ ... }});

**destroy**`model.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…

- keys
- values
- pairs
- invert
- pick
- omit
- chain
- isEmpty

user.pick('first\_name', 'last\_name', 'email');

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

**validate**`model.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.

**validationError**`model.validationError`
The value returned by validate during the last failed validation.

**isValid**`model.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);
}

**url**`model.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"

**urlRoot**`model.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());

**parse**`model.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

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

**isNew**`model.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.

**hasChanged**`model.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")) {
...
}
});

**changedAttributes**`model.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.

**previous**`model.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"});

**previousAttributes**`model.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", ...)

**extend**`Backbone.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.

**model**`collection.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);
}
}

});

**modelId**`collection.modelId(attrs, idAttribute)`
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 given idAttribute within the attrs, or failing that, id. If your collection uses a model factory and the id ranges of those models might collide, 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);

**preinitialize**`new 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 / initialize**`new 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
});

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

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

**toJSON**`collection.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));

**sync**`collection.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.

- forEach (each)
- map (collect)
- reduce (foldl, inject)
- reduceRight (foldr)
- find (detect)
- findIndex
- findLastIndex
- filter (select)
- reject
- every (all)
- some (any)
- contains (includes)
- invoke
- max
- min
- sortBy
- groupBy
- shuffle
- toArray
- size
- first (head, take)
- initial
- rest (tail, drop)
- last
- without
- indexOf
- lastIndexOf
- isEmpty
- chain
- difference
- sample
- partition
- countBy
- indexBy

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);

**add**`collection.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. This is a variant of set with the same options and return value, but it always adds and never removes. 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.

**remove**`collection.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.

**reset**`collection.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.

**set**`collection.set(models, [options])`
The **set** method performs a "smart" update of the collection with the passed list of models. If a model in the list isn't 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, with a single "update" event at the end. Returns the touched models in the collection. If you'd like to customize this behavior, you can change it with options: {add: false}, {remove: false}, or {merge: false}.

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. If you set a comparator, the collection will automatically sort itself and trigger a "sort" event, unless you pass {sort: false} or use the {at: index} option. Pass {at: index} to splice the model(s) into the collection at the specified index.

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.

**get**`collection.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);

**at**`collection.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.

**push**`collection.push(model, [options])`
Like add, but always adds a model at the end of the collection and never sorts.

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

**unshift**`collection.unshift(model, [options])`
Like add, but always adds a model at the beginning of the collection and never sorts.

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

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

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

**comparator**`collection.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.

**sort**`collection.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.

**pluck**`collection.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));

**where**`collection.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);

**findWhere**`collection.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.

**url**`collection.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';
}
});

**parse**`collection.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;
}
});

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

**fetch**`collection.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.

**create**`collection.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"
});

**mixin**`Backbone.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.

**extend**`Backbone.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) {
...
}

});

**routes**`router.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) {
...
});

**preinitialize**`new 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 / initialize**`new 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.

**route**`router.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) { ... }

**navigate**`router.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});

**execute**`router.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. It forwards the "route" and "route\[name\]" events of the matching router, or "notfound" when no route in any router matches the current URL. 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.

**start**`Backbone.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/"}).

The value provided for root will be normalized to include a leading and trailing slash. When navigating to a route the default behavior is to exclude the trailing slash from the URL (e.g., /public/search?query=...). If you prefer to include the trailing slash (e.g., /public/search/?query=...) use Backbone.history.start({trailingSlash: true}). URLs will always contain a leading slash. When root is / URLs will look like /?query=... regardless of the value of trailingSlash.

When called, if a route succeeds with a match for the current URL, Backbone.history.start() returns true and the "route" and "route\[name\]" events are triggered. If no defined route matches the current URL, it returns false and "notfound" is triggered instead.

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

**ajax**`Backbone.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.

**emulateHTTP**`Backbone.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.

**emulateJSON**`Backbone.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.

**extend**`Backbone.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.

**preinitialize**`new 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 / initialize**`new 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
});

**el**`view.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);

**$el**`view.$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);

**setElement**`view.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.

**attributes**`view.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()
};
}
});

**template**`view.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(...)
});

**render**`view.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.

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

**events**`view.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()});
}
}
});

**delegateEvents**`delegateEvents([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});
},

...

});

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

## Utility

**Backbone.noConflict**`var 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');

**debugInfo**`debugInfo();`
In the unfortunate event that you need to submit a bug report, this function makes it easier to provide detailed information about your setup. It prints a JSON object with version information about Backbone and its dependencies through console.debug. It also returns this object in case you want to inspect it in code.

debugInfo comes in a separate module that ships with the edge version and releases later than 1.5.0. It is available in UMD format under the same prefix as backbone.js, but with debug-info.js as the file name. It is also experimentally available in ES module format under backbone/modules/.

<!-- browser embeds -->
<script src="some-path-or-url/backbone.js"></script>
<script src="some-path-or-url/debug-info.js"></script>
<script>
Backbone.debugInfo();
</script>

// CommonJS
require('backbone/debug-info.js')();

// ESM
import debugInfo from 'backbone/modules/debug-info.js';
debugInfo();

## F.A.Q.

**Why use Backbone, not \[other framework X\]?**
If your eye hasn't already been caught by the adaptability and elan on display in the above list of examples, we can get more specific: Backbone.js aims to provide the common foundation that data-rich web applications with ambitious interfaces require — while very deliberately avoiding painting you into a corner by making any decisions that you're better equipped to make yourself.

- The focus is on supplying you with helpful methods to manipulate and query your data, not on HTML widgets or reinventing the JavaScript object model.
- Backbone does not force you to use a single template engine. Views can bind to HTML constructed in your favorite way.
- It's smaller. There are fewer kilobytes for your browser or phone to download, and less *conceptual* surface area. You can read and understand the source in an afternoon.
- It doesn't depend on stuffing application logic into your HTML. There's no embedded JavaScript, template logic, or binding hookup code in data- or ng- attributes, and no need to invent your own HTML tags.
- Synchronous events are used as the fundamental building block, not a difficult-to-reason-about run loop, or by constantly polling and traversing your data structures to hunt for changes. And if you want a specific event to be asynchronous and aggregated, no problem.
- Backbone scales well, from embedded widgets to massive apps.
- Backbone is a library, not a framework, and plays well with others. You can embed Backbone widgets in Dojo apps without trouble, or use Backbone models as the data backing for D3 visualizations (to pick two entirely random examples).
- "Two-way data-binding" is avoided. While it certainly makes for a nifty demo, and works for the most basic CRUD, it doesn't tend to be terribly useful in your real-world app. Sometimes you want to update on every keypress, sometimes on blur, sometimes when the panel is closed, and sometimes when the "save" button is clicked. In almost all cases, simply serializing the form to JSON is faster and easier. All that aside, if your heart is set, go for it.
- There's no built-in performance penalty for choosing to structure your code with Backbone. And if you do want to optimize further, thin models and templates with flexible granularity make it easy to squeeze every last drop of potential performance out of, say, IE8.

**There's More Than One Way To Do It**
It's common for folks just getting started to treat the examples listed on this page as some sort of gospel truth. In fact, Backbone.js is intended to be fairly agnostic about many common patterns in client-side code. For example...

**References between Models and Views** can be handled several ways. Some people like to have direct pointers, where views correspond 1:1 with models (model.view and view.model). Others prefer to have intermediate "controller" objects that orchestrate the creation and organization of views into a hierarchy. Others still prefer the evented approach, and always fire events instead of calling methods directly. All of these styles work well.

**Batch operations** on Models are common, but often best handled differently depending on your server-side setup. Some folks don't mind making individual Ajax requests. Others create explicit resources for RESTful batch operations: /notes/batch/destroy?ids=1,2,3,4. Others tunnel REST over JSON, with the creation of "changeset" requests:

{
"create":  \[array of models to create\]
"update":  \[array of models to update\]
"destroy": \[array of model ids to destroy\]
}

**Feel free to define your own events.** Backbone.Events is designed so that you can mix it in to any JavaScript object or prototype. Since you can use any string as an event, it's often handy to bind and trigger your own custom events: model.on("selected:true") or model.on("editing")

**Render the UI** as you see fit. Backbone is agnostic as to whether you use Underscore templates, Mustache.js, direct DOM manipulation, server-side rendered snippets of HTML, or jQuery UI in your render function. Sometimes you'll create a view for each model ... sometimes you'll have a view that renders thousands of models at once, in a tight loop. Both can be appropriate in the same app, depending on the quantity of data involved, and the complexity of the UI.

**Nested Models & Collections**
It's common to nest collections inside of models with Backbone. For example, consider a Mailbox model that contains many Message models. One nice pattern for handling this is have a this.messages collection for each mailbox, enabling the lazy-loading of messages, when the mailbox is first opened ... perhaps with MessageList views listening for "add" and "remove" events.

var Mailbox = Backbone.Model.extend({

initialize: function() {
this.messages = new Messages;
this.messages.url = '/mailbox/' + this.id + '/messages';
this.messages.on("reset", this.updateCounts);
},

...

});

var inbox = new Mailbox;

// And then, when the Inbox is opened:

inbox.messages.fetch({reset: true});

If you're looking for something more opinionated, there are a number of Backbone plugins that add sophisticated associations among models, available on the wiki.

Backbone doesn't include direct support for nested models and collections or "has many" associations because there are a number of good patterns for modeling structured data on the client side, and *Backbone should provide the foundation for implementing any of them.* You may want to…

- Mirror an SQL database's structure, or the structure of a NoSQL database.
- Use models with arrays of "foreign key" ids, and join to top level collections (a-la tables).
- For associations that are numerous, use a range of ids instead of an explicit list.
- Avoid ids, and use direct references, creating a partial object graph representing your data set.
- Lazily load joined models from the server, or lazily deserialize nested models from JSON documents.

**Loading Bootstrapped Models**
When your app first loads, it's common to have a set of initial models that you know you're going to need, in order to render the page. Instead of firing an extra AJAX request to fetch them, a nicer pattern is to have their data already bootstrapped into the page. You can then use reset to populate your collections with the initial data. At DocumentCloud, in the ERB template for the workspace, we do something along these lines:

<script>
var accounts = new Backbone.Collection;
accounts.reset(<%= @accounts.to\_json %>);
var projects = new Backbone.Collection;
projects.reset(<%= @projects.to\_json(:collaborators => true) %>);
</script>

You have to escape </ within the JSON string, to prevent JavaScript injection attacks.

**Extending Backbone**
Many JavaScript libraries are meant to be insular and self-enclosed, where you interact with them by calling their public API, but never peek inside at the guts. Backbone.js is *not* that kind of library.

Because it serves as a foundation for your application, you're meant to extend and enhance it in the ways you see fit — the entire source code is annotated to make this easier for you. You'll find that there's very little there apart from core functions, and most of those can be overridden or augmented should you find the need. If you catch yourself adding methods to Backbone.Model.prototype, or creating your own base subclass, don't worry — that's how things are supposed to work.

**How does Backbone relate to "traditional" MVC?**
Different implementations of the Model-View-Controller pattern tend to disagree about the definition of a controller. If it helps any, in Backbone, the View class can also be thought of as a kind of controller, dispatching events that originate from the UI, with the HTML template serving as the true view. We call it a View because it represents a logical chunk of UI, responsible for the contents of a single DOM element.

Comparing the overall structure of Backbone to a server-side MVC framework like **Rails**, the pieces line up like so:

- **Backbone.Model** – Like a Rails model minus the class methods. Wraps a row of data in business logic.
- **Backbone.Collection** – A group of models on the client-side, with sorting/filtering/aggregation logic.
- **Backbone.Router** – Rails routes.rb + Rails controller actions. Maps URLs to functions.
- **Backbone.View** – A logical, re-usable piece of UI. Often, but not always, associated with a model.
- **Client-side Templates** – Rails .html.erb views, rendering a chunk of HTML.

**Binding "this"**
Perhaps the single most common JavaScript "gotcha" is the fact that when you pass a function as a callback, its value for this is lost. When dealing with events and callbacks in Backbone, you'll often find it useful to rely on listenTo or the optional context argument that many of Underscore and Backbone's methods use to specify the this that will be used when the callback is later invoked. (See \_.each, \_.map, and object.on, to name a few). View events are automatically bound to the view's context for you. You may also find it helpful to use \_.bind and \_.bindAll from Underscore.js.

var MessageList = Backbone.View.extend({

initialize: function() {
var messages = this.collection;
messages.on("reset", this.render, this);
messages.on("add", this.addMessage, this);
messages.on("remove", this.removeMessage, this);

messsages.each(this.addMessage, this);
}

});

// Later, in the app...

Inbox.messages.add(newMessage);

**Working with Rails**
Backbone.js was originally extracted from a Rails application; getting your client-side (Backbone) Models to sync correctly with your server-side (Rails) Models is painless, but there are still a few things to be aware of.

By default, Rails versions prior to 3.1 add an extra layer of wrapping around the JSON representation of models. You can disable this wrapping by setting:

ActiveRecord::Base.include\_root\_in\_json = false

... in your configuration. Otherwise, override parse to pull model attributes out of the wrapper. Similarly, Backbone PUTs and POSTs direct JSON representations of models, where by default Rails expects namespaced attributes. You can have your controllers filter attributes directly from params, or you can override toJSON in Backbone to add the extra wrapping Rails expects.

## Examples

The list of examples that follows, while long, is not exhaustive — nor in any way current. If you've worked on an app that uses Backbone, please add it to the wiki page of Backbone apps.

Jérôme Gravel-Niquet has contributed a Todo List application that is bundled in the repository as Backbone example. If you're wondering where to get started with Backbone in general, take a moment to read through the annotated source. The app uses a LocalStorage adapter to transparently save all of your todos within your browser, instead of sending them to a server. Jérôme also has a version hosted at localtodos.com.

## DocumentCloud

The DocumentCloud workspace is built on Backbone.js, with *Documents*, *Projects*, *Notes*, and *Accounts* all as Backbone models and collections. If you're interested in history — both Underscore.js and Backbone.js were originally extracted from the DocumentCloud codebase, and packaged into standalone JS libraries.

## USA Today

USA Today takes advantage of the modularity of Backbone's data/model lifecycle — which makes it simple to create, inherit, isolate, and link application objects — to keep the codebase both manageable and efficient. The new website also makes heavy use of the Backbone Router to control the page for both pushState-capable and legacy browsers. Finally, the team took advantage of Backbone's Event module to create a PubSub API that allows third parties and analytics packages to hook into the heart of the app.

## Rdio

New Rdio was developed from the ground up with a component based framework based on Backbone.js. Every component on the screen is dynamically loaded and rendered, with data provided by the Rdio API. When changes are pushed, every component can update itself without reloading the page or interrupting the user's music. All of this relies on Backbone's views and models, and all URL routing is handled by Backbone's Router. When data changes are signaled in realtime, Backbone's Events notify the interested components in the data changes. Backbone forms the core of the new, dynamic, realtime Rdio web and *desktop* applications.

## Hulu

Hulu used Backbone.js to build its next generation online video experience. With Backbone as a foundation, the web interface was rewritten from scratch so that all page content can be loaded dynamically with smooth transitions as you navigate. Backbone makes it easy to move through the app quickly without the reloading of scripts and embedded videos, while also offering models and collections for additional data manipulation support.

## Quartz

Quartz sees itself as a digitally native news outlet for the new global economy. Because Quartz believes in the future of open, cross-platform web applications, they selected Backbone and Underscore to fetch, sort, store, and display content from a custom WordPress API. Although qz.com uses responsive design for phone, tablet, and desktop browsers, it also takes advantage of Backbone events and views to render device-specific templates in some cases.

## Earth

Earth.nullschool.net displays real-time weather conditions on an interactive animated globe, and Backbone provides the foundation upon which all of the site's components are built. Despite the presence of several other JavaScript libraries, Backbone's non-opinionated design made it effortless to mix-in the Events functionality used for distributing state changes throughout the page. When the decision was made to switch to Backbone, large blocks of custom logic simply disappeared.

## Vox

Vox Media, the publisher of SB Nation, The Verge, Polygon, Eater, Racked, Curbed, and Vox.com, uses Backbone throughout Chorus, its home-grown publishing platform. Backbone powers the liveblogging platform and commenting system used across all Vox Media properties; Coverage, an internal editorial coordination tool; SB Nation Live, a live event coverage and chat tool; and Vox Cards, Vox.com's highlighter-and-index-card inspired app for providing context about the news.

## Gawker Media

Kinja is Gawker Media's publishing platform designed to create great stories by breaking down the lines between the traditional roles of content creators and consumers. Everyone — editors, readers, marketers — have access to the same tools to engage in passionate discussion and pursue the truth of the story. Sharing, recommending, and following within the Kinja ecosystem allows for improved information discovery across all the sites.

Kinja is the platform behind Gawker, Gizmodo, Lifehacker, io9 and other Gawker Media blogs. Backbone.js underlies the front-end application code that powers everything from user authentication to post authoring, commenting, and even serving ads. The JavaScript stack includes Underscore.js and jQuery, with some plugins, all loaded with RequireJS. Closure templates are shared between the Play! Framework based Scala application and Backbone views, and the responsive layout is done with the Foundation framework using SASS.

## Flow

MetaLab used Backbone.js to create Flow, a task management app for teams. The workspace relies on Backbone.js to construct task views, activities, accounts, folders, projects, and tags. You can see the internals under window.Flow.

## Gilt Groupe

Gilt Groupe uses Backbone.js to build multiple applications across their family of sites. Gilt's mobile website uses Backbone and Zepto.js to create a blazing-fast shopping experience for users on-the-go, while Gilt Live combines Backbone with WebSockets to display the items that customers are buying in real-time. Gilt's search functionality also uses Backbone to filter and sort products efficiently by moving those actions to the client-side.

## Enigma

Enigma is a portal amassing the largest collection of public data produced by governments, universities, companies, and organizations. Enigma uses Backbone Models and Collections to represent complex data structures; and Backbone's Router gives Enigma users unique URLs for application states, allowing them to navigate quickly through the site while maintaining the ability to bookmark pages and navigate forward and backward through their session.

## NewsBlur

NewsBlur is an RSS feed reader and social news network with a fast and responsive UI that feels like a native desktop app. Backbone.js was selected for a major rewrite and transition from spaghetti code because of its powerful yet simple feature set, easy integration, and large community. If you want to poke around under the hood, NewsBlur is also entirely open-source.

## WordPress.com

WordPress.com is the software-as-a-service version of WordPress. It uses Backbone.js Models, Collections, and Views in its Notifications system. Backbone.js was selected because it was easy to fit into the structure of the application, not the other way around. Automattic (the company behind WordPress.com) is integrating Backbone.js into the Stats tab and other features throughout the homepage.

## Foursquare

Foursquare is a fun little startup that helps you meet up with friends, discover new places, and save money. Backbone Models are heavily used in the core JavaScript API layer and Views power many popular features like the homepage map and lists.

## Bitbucket

Bitbucket is a free source code hosting service for Git and Mercurial. Through its models and collections, Backbone.js has proved valuable in supporting Bitbucket's REST API, as well as newer components such as in-line code comments and approvals for pull requests. Mustache templates provide server and client-side rendering, while a custom Google Closure inspired life-cycle for widgets allows Bitbucket to decorate existing DOM trees and insert new ones.

## Disqus

Disqus chose Backbone.js to power the latest version of their commenting widget. Backbone’s small footprint and easy extensibility made it the right choice for Disqus’ distributed web application, which is hosted entirely inside an iframe and served on thousands of large web properties, including IGN, Wired, CNN, MLB, and more.

## Delicious

Delicious is a social bookmarking platform making it easy to save, sort, and store bookmarks from across the web. Delicious uses Chaplin.js, Backbone.js and AppCache to build a full-featured MVC web app. The use of Backbone helped the website and mobile apps share a single API service, and the reuse of the model tier made it significantly easier to share code during the recent Delicious redesign.

## Khan Academy

Khan Academy is on a mission to provide a free world-class education to anyone anywhere. With thousands of videos, hundreds of JavaScript-driven exercises, and big plans for the future, Khan Academy uses Backbone to keep frontend code modular and organized. User profiles and goal setting are implemented with Backbone, jQuery and Handlebars, and most new feature work is being pushed to the client side, greatly increasing the quality of the API.

## IRCCloud

IRCCloud is an always-connected IRC client that you use in your browser — often leaving it open all day in a tab. The sleek web interface communicates with an Erlang backend via websockets and the IRCCloud API. It makes heavy use of Backbone.js events, models, views and routing to keep your IRC conversations flowing in real time.

## Pitchfork

Pitchfork uses Backbone.js to power its site-wide audio player, Pitchfork.tv, location routing, a write-thru page fragment cache, and more. Backbone.js (and Underscore.js) helps the team create clean and modular components, move very quickly, and focus on the site, not the spaghetti.

## Spin

Spin pulls in the latest news stories from their internal API onto their site using Backbone models and collections, and a custom sync method. Because the music should never stop playing, even as you click through to different "pages", Spin uses a Backbone router for navigation within the site.

## ZocDoc

ZocDoc helps patients find local, in-network doctors and dentists, see their real-time availability, and instantly book appointments. On the public side, the webapp uses Backbone.js to handle client-side state and rendering in search pages and doctor profiles. In addition, the new version of the doctor-facing part of the website is a large single-page application that benefits from Backbone's structure and modularity. ZocDoc's Backbone classes are tested with Jasmine, and delivered to the end user with Cassette.

## Walmart Mobile

Walmart used Backbone.js to create the new version of their mobile web application and created two new frameworks in the process. Thorax provides mixins, inheritable events, as well as model and collection view bindings that integrate directly with Handlebars templates. Lumbar allows the application to be split into modules which can be loaded on demand, and creates platform specific builds for the portions of the web application that are embedded in Walmart's native Android and iOS applications.

## Groupon Now!

Groupon Now! helps you find local deals that you can buy and use right now. When first developing the product, the team decided it would be AJAX heavy with smooth transitions between sections instead of full refreshes, but still needed to be fully linkable and shareable. Despite never having used Backbone before, the learning curve was incredibly quick — a prototype was hacked out in an afternoon, and the team was able to ship the product in two weeks. Because the source is minimal and understandable, it was easy to add several Backbone extensions for Groupon Now!: changing the router to handle URLs with querystring parameters, and adding a simple in-memory store for caching repeated requests for the same data.

## Basecamp

37Signals chose Backbone.js to create the calendar feature of its popular project management software Basecamp. The Basecamp Calendar uses Backbone.js models and views in conjunction with the Eco templating system to present a polished, highly interactive group scheduling interface.

## Slavery Footprint

Slavery Footprint allows consumers to visualize how their consumption habits are connected to modern-day slavery and provides them with an opportunity to have a deeper conversation with the companies that manufacture the goods they purchased. Based in Oakland, California, the Slavery Footprint team works to engage individuals, groups, and businesses to build awareness for and create deployable action against forced labor, human trafficking, and modern-day slavery through online tools, as well as off-line community education and mobilization programs.

## Stripe

Stripe provides an API for accepting credit cards on the web. Stripe's management interface was recently rewritten from scratch in CoffeeScript using Backbone.js as the primary framework, Eco for templates, Sass for stylesheets, and Stitch to package everything together as CommonJS modules. The new app uses Stripe's API directly for the majority of its actions; Backbone.js models made it simple to map client-side models to their corresponding RESTful resources.

## Airbnb

Airbnb uses Backbone in many of its products. It started with Airbnb Mobile Web (built in six weeks by a team of three) and has since grown to Wish Lists, Match, Search, Communities, Payments, and Internal Tools.

## SoundCloud Mo