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

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

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

Backbone is an open-source component of DocumentCloud.

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

Development Version (0.9.2) | 52kb, Full source, lots of comments
Production Version (0.9.2) | 5.6kb, Packed and gzipped

Backbone's only hard dependency is Underscore.js ( > 1.3.1). For RESTful persistence, history support via Backbone.Router and DOM manipulation with Backbone.View, include json2.js, and either jQuery ( > 1.4.2) or Zepto.

## Introduction

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

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

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

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

## Upgrading to 0.9

Backbone's 0.9 series should be considered as a release candidate for an upcoming 1.0. Some APIs have changed, and while there is a change log available, and many new features to take advantage of, there are a few specific changes where you'll need to take care:

- If you've ever manually set `this.el` in a Backbone View to be a particular DOM element, you'll want to use setElement instead.
- Creating and destroying models is now optimistic. Pass `{wait: true}` if you need the previous behavior of waiting for the server to acknowledge success. You can now also pass `{wait: true}` to save calls.
- If you have been writing a fair amount of `$(view.el)`, there's now a cached reference for that jQuery object: $el.
- If you're upgrading, make sure you also upgrade your version of Underscore.js to the latest — 1.3.1 or greater.
- `model.set` will no longer trigger change events when setting a value with `{silent: true}` then setting it back to its original value. Similarly, after changing an attribute silently, that `change:attribute` event will fire during the next change.
- Since `view.$(selector)` is now equivalent to `view.$el.find(selector)` rather than `$(selector, view.el)` it can no longer be used when `selector` is an HTML string or DOM element.

## 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", ...);

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

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

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

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, all event callbacks on the object 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();

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.

## 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.call(this, attributes, options);
        ...
      }
    });

constructor / initialize `new Model([attributes])`
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.

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 models state, a `"change"` event will be triggered, unless `{silent: true}` is passed as an option. 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");

If the model has a validate method, it will be validated before the attributes are set, no changes will occur if the validation fails, and set will return `false`. Otherwise, set returns a reference to the model. You may also pass an `error` callback in the options, which will be invoked instead of triggering an `"error"` event, should validation fail. If `{silent: true}` is passed as an option, the validation is deferred until the next change.

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. 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. 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`.

    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. Client ids take the form: `c1, c2, c3 ...`

attributes `model.attributes`
The attributes property is the internal hash containing the model's 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 toJSON instead.

changed `model.changed`
The changed property is the internal hash containing all the attributes that have changed since the last `"change"` event was triggered. Please do not update changed directly. Its state is maintained internally by set and change. 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.

toJSON `model.toJSON()`
Return a copy of the model's attributes for JSON stringification. This can be used for persistence, serialization, or for augmentation before being handed off to a view. 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));

fetch `model.fetch([options])`
Resets the model's state 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. A `"change"` event will be triggered if the server's state differs from the current attributes. Accepts `success` and `error` callbacks in the options hash, which are passed `(model, response)` 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`).

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

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

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

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

    book.save();

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

save accepts `success` and `error` callbacks in the options hash, which are passed `(model, response)` as arguments. The `error` callback will also be invoked if the model has a `validate` method, and validation fails. 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. Triggers a `"destroy"` event on the model, which will bubble up through any collections that contain it, 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) {
      ...
    }});

validate `model.validate(attributes)`
This method is left undefined, and you're encouraged to override it with your custom validation logic, if you have any that can be performed in JavaScript. validate is called before `set` and `save`, and is passed the model attributes updated with the values from `set` or `save`. If the attributes are valid, don't return anything from validate; if they are invalid, return an error of your choosing. It can be as simple as a string error message to be displayed, or a complete error object that describes the error programmatically. If validate returns an error, `set` and `save` will not continue, and the model attributes will not be modified. Failed validations trigger an `"error"` event.

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

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

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

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

`"error"` events are useful for providing coarse-grained error messages at the model or collection level, but if you have a specific view that can better handle the error, you may override and suppress the event by passing an `error` callback directly:

    account.set({access: "unlimited"}, {
      error: function(model, error) {
        alert(error);
      }
    });

isValid `model.isValid()`
Models may enter an invalid state if you make changes to them silently ... useful when dealing with form input. Call `model.isValid()` to check if the model is currently in a valid state, according to your `validate` function.

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]"`, falling back to `"/[urlRoot]/id"` if the model is not part of a collection.

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"`
Note that `urlRoot` may also be defined as a function.

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

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

    alert(solaris.url());

parse `model.parse(response)`
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, you'll notice that Rails' 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.

change `model.change()`
Manually trigger the `"change"` event and a `"change:attribute"` event for each attribute that has changed. If you've been passing `{silent: true}` to the set function in order to aggregate rapid changes to a model, you'll want to call `model.change()` when you're all finished.

hasChanged `model.hasChanged([attribute])`
Has the model changed since the last `"change"` event? If an attribute is passed, returns `true` if that specific attribute has changed.

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

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

changedAttributes `model.changedAttributes([attributes])`
Retrieve a hash of only the model's attributes that have changed. 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`
Override this property to specify the model class that the collection contains. If defined, you can pass raw attributes objects (and arrays) to add, create, and reset, and the attributes will be converted into a model of the proper type.

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

constructor / initialize `new Collection([models], [options])`
When creating a Collection, you may choose to pass in the initial array of models. The collection's comparator function may be included as an option. If you define an initialize function, it will be invoked when the collection is created.

    var tabs = new TabSet([tab1, tab2, tab3]);

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

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

    alert(JSON.stringify(collection));

Underscore Methods (28)
Backbone proxies to Underscore.js to provide 28 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…

- forEach (each)
- map
- reduce (foldl, inject)
- reduceRight (foldr)
- find (detect)
- filter (select)
- reject
- every (all)
- some (any)
- include
- invoke
- max
- min
- sortBy
- groupBy
- sortedIndex
- shuffle
- toArray
- size
- first
- initial
- rest
- last
- without
- indexOf
- lastIndexOf
- isEmpty
- chain

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

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

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

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

add `collection.add(models, [options])`
Add a model (or an array of models) to the collection. Fires an `"add"` event, which you can pass `{silent: true}` to suppress. If a model property is defined, you may also pass raw attributes objects, and have them be vivified as instances of the model. Pass `{at: index}` to splice the model into the collection at the specified `index`. Likewise, if you're a callback listening to a collection's `"add"` event, `options.index` will tell you the index at which the model is being added to the collection.

    var ships = new Backbone.Collection;

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

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

remove `collection.remove(models, [options])`
Remove a model (or an array of models) from the collection. Fires a `"remove"` event, which you can use `silent` to suppress. If you're a callback listening to the `"remove"` event, the index at which the model is being removed from the collection is available as `options.index`.

get `collection.get(id)`
Get a model from a collection, specified by id.

    var book = Library.get(110);

getByCid `collection.getByCid(cid)`
Get a model from a collection, specified by client id. The client id is the `.cid` property of the model, automatically assigned whenever a model is created. Useful for models which have not yet been saved to the server, and do not yet have true ids.

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.

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

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

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

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

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 function on a collection. If you define a comparator, it will be used to maintain the collection in sorted order. This means that as models are added, they are inserted at the correct index in `collection.models`. Comparator function can be defined as either a sortBy (pass a function that takes a single argument), or as a sort (pass a comparator function that expects two arguments).

"sortBy" comparator functions take a model and return a numeric or string value by which the model should be ordered relative to others. "sort" comparator functions take two models, and return `-1` if the first model should come before the second, `0` if they are of the same rank and `1` if the first model should come after.

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

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

    chapters.comparator = function(chapter) {
      return chapter.get("page");
    };

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

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

Collections with comparator functions 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. You don't need to call this under normal circumstances, as a collection with a comparator function will maintain itself in proper sort order at all times. Calling sort triggers the collection's `"reset"` event, unless silenced by passing `{silent: true}`

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);

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)`
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. Note that afterwards, if your model class already has a `parse` function, it will be run against each fetched model.

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

fetch `collection.fetch([options])`
Fetch the default set of models for this collection from the server, resetting the collection when they arrive. The options hash takes `success` and `error` callbacks which will be passed `(collection, response)` as arguments. When the model data returns from the server, the collection will 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();

If you'd like to add the incoming models to the current collection, instead of replacing the collection's contents, pass `{add: true}` as an option to fetch.

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.

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 at the end. Pass `{silent: true}` to suppress the `"reset"` event. Using reset with no arguments is useful as a way to empty the collection.

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.

create `collection.create(attributes, [options])`
Convenience to create a new instance of a model within a collection. Delegates to Backbone.sync and returns a jqXHR if validation is successful, and `false` otherwise. 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 model, or `false` if a validation error prevented the model from being created. In order for this to work, you should set the model property of the collection. The create method can accept either an attributes hash or an existing, unsaved model object.

Creating a model will cause an immediate `"add"` event to be triggered on the collection, as well as a `"sync"` event, once the model has been successfully created on the server. Pass `{wait: true}` if you'd like to wait for the server before adding the new model to the collection.

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

    var NYPL = new Library;

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

## Backbone.Router

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

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

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

    var Workspace = Backbone.Router.extend({

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

      help: function() {
        ...
      },

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

    });

routes `router.routes`
The routes hash maps URLs with parameters to functions on your router, 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.

For example, a route of `"search/:query/p:page"` will match a fragment of `#search/obama/p2`, passing `"obama"` and `"2"` to the action. A route of `"file/*path"` will match `#file/nested/folder/file.txt`, passing `"nested/folder/file.txt"` to the action.

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) {
      ...
    });

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.

    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 wish to also 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});

## Backbone.history

History serves as a global router (per frame) to handle `hashchange` events or `pushState`, match the appropriate route, and trigger callbacks. You shouldn't ever have to create one of these yourself — you should use the reference to `Backbone.history` that will be created for you automatically if you make use of Routers with routes.

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.

To indicate that you'd like to use HTML5 `pushState` support in your application, use `Backbone.history.start({pushState: true})`.

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

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

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

Because hash-based history in Internet Explorer relies on an `<iframe>`, be sure to only call `start()` 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/Zepto).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.

The sync function may be overriden 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`
- delete → DELETE `/collection/id`

As an example, a Rails handler responding to an `"update"` call from `Backbone` might look like this: (In real code, never use `update_attributes` blindly, and always whitelist the attributes you allow to be changed.)

    def update
      account = Account.find params[:id]
      account.update_attributes params
      render :json => account
    end

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

emulateHTTP `Backbone.emulateHTTP = true`
If you want to work with a legacy web server that doesn't support Backbones's default REST/HTTP approach, you may choose to turn on `Backbone.emulateHTTP`. Setting this option will fake `PUT` 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"
      },

      render: function() {
        ...
      }

    });

constructor / initialize `new View([options])`
When creating a new View, the options you pass are attached to the view as `this.options`, for future reference. There are several special options that, if passed, will be attached directly to the view: `model`, `collection`, `el`, `id`, `className`, `tagName` and `attributes`. 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` is created from the view's `tagName`, `className`, `id` and `attributes` properties, if specified. If not, el is an empty `div`.

    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 (or Zepto) 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 or Zepto)`view.$(selector)`
If jQuery or Zepto 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()
        };
      }
    });

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({
      render: function() {
        $(this.el).html(this.template(this.model.toJSON()));
        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've already XSS-sanitized your interpolated data.

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()`
Convenience function for removing the view from the DOM. Equivalent to calling `$(view.el).remove();`

make `view.make(tagName, [attributes], [content])`
Convenience function for creating a DOM element of the given type (tagName), with optional attributes and HTML content. Used internally to create the initial `view.el`.

    var view = new Backbone.View;

    var el = view.make("b", {"class": "bold"}, "Bold! ");

    $("#make-demo").append(el);

delegateEvents `delegateEvents([events])`
Uses jQuery's `delegate` 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 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.toJSON()));
        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 Functions

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(...);

setDomLibrary `Backbone.setDomLibrary(jQueryNew);`
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 function for you.

## Examples

The list of examples that follows, while long, is not exhaustive. 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 that uses a MooTools-backed version of Backbone instead of jQuery.

## 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.

## LinkedIn Mobile

LinkedIn used Backbone.js to create its next-generation HTML5 mobile web app. Backbone made it easy to keep the app modular, organized and extensible so that it was possible to program the complexities of LinkedIn's user experience. The app also uses Zepto, Underscore.js, SASS, iScroll, HTML5 LocalStorage and Canvas.

## 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`.

## AudioVroom

AudioVroom is a free music streaming app that allows you to listen to your Facebook friends like radio stations. It relies heavily on Backbone (views and song management) and also features a responsive grid-based design (using CSS3 media-queries) to deliver a unified user experience on desktops, mobiles, and tablets alike. Being a pure Backbone app, AudioVroom is only 60kb compressed, and can be entirely hosted on the CDN.

## 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.

## Wunderkit

Wunderkit is a productivity and social collaboration platform. It uses Backbone.js as the foundation for the single-page application, which is backed by a RESTful Rails API. The freedom and agility that Backbone gives to developers made it possible to build Wunderkit in a very short time and extend it with custom features: a write-through cache using HTML5 localStorage, and a view hierarchy extension to easily manage trees of sub-views. Aside from Backbone, Wunderkit also depends on jQuery, Underscore, Require.js, LESS and doT.js templates.

## 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.

## Do

Do is a social productivity app that makes it easy to work on tasks, track projects, and take notes with your team. The Do.com web application was built from the ground up to work seamlessly on your smartphone, tablet and computer. The team used Backbone, CoffeeScript and Handlebars to build a full-featured app in record time and rolled their own extensions for complex navigation and model sync support.

## Posterous

Posterous Spaces is built on Backbone. The models and collections mirror the public Posterous API. Backbone made it easy for the team to create a JavaScript-heavy application with complex interactions and state maintenance. Spaces also uses CoffeeScript, Underscore.js, Haml.js, Sass, Compass, and of course jQuery.

## 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 Mobile

37Signals used Backbone.js to create Basecamp Mobile, the mobile version of their popular project management software. You can access all your Basecamp projects, post new messages, and comment on milestones (all represented internally as Backbone.js models).

## 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 modulas. 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 Mobile

Airbnb used Backbone.js and CoffeeScript to quickly build Airbnb Mobile in six weeks with a team of three. The mobile version of Airbnb lets you discover and book rental spaces directly from your phone: from a private apartment to a private island...

## Diaspora

Diaspora is a distributed social network, formed from a number of independently operated pods. You own your personal data, and control with whom you share. All of Diaspora is open-source code, built with Rails and Backbone.js.

## SoundCloud Mobile

SoundCloud is the leading sound sharing platform on the internet, and Backbone.js provides the foundation for SoundCloud Mobile. The project uses the public SoundCloud API as a data source (channeled through a nginx proxy), jQuery templates for the rendering, Qunit and PhantomJS for the testing suite. The JS code, templates and CSS are built for the production deployment with various Node.js tools like ready.js, Jake, jsdom. The Backbone.History was modified to support the HTML5 `history.pushState`. Backbone.sync was extended with an additional SessionStorage based cache layer.

## Pandora

When Pandora redesigned their site in HTML5, they chose Backbone.js to help manage the user interface and interactions. For example, there's a model that represents the "currently playing track", and multiple views that automatically update when the current track changes. The station list is a collection, so that when stations are added or changed, the UI stays up to date.

## Code School

Code School courses teach people about various programming topics like CoffeeScript, CSS, Ruby on Rails, and more. The new Code School course challenge page is built from the ground up on Backbone.js, using everything it has to offer: the router, collections, models, and complex event handling. Before, the page was a mess of jQuery DOM manipulation and manual Ajax calls. Backbone.js helped introduce a new way to think about developing an organized front-end application in Javascript.

## CloudApp

CloudApp is simple file and link sharing for the Mac. Backbone.js powers the web tools which consume the documented API to manage Drops. Data is either pulled manually or pushed by Pusher and fed to Mustache templates for rendering. Check out the annotated source code to see the magic.

## SeatGeek

SeatGeek's stadium ticket maps were originally developed with Prototype.js. Moving to Backbone.js and jQuery helped organize a lot of the UI code, and the increased structure has made adding features a lot easier. SeatGeek is also in the process of building a mobile interface that will be Backbone.js from top to bottom.

## Grove.io

Grove.io provides hosted IRC for teams. Backbone.js powers Grove's web client together with Handlebars.js templating. Updates to chat stream are pulled in realtime using long-polling.

## Kicksend

Kicksend is a real-time file sharing platform that helps everyday people send and receive files of any size with their friends and family. Kicksend's web application makes extensive use of Backbone.js to model files, friends, lists and activity streams.

## Shortmail

410 Labs uses Backbone.js at Shortmail.com to build a fast and responsive inbox, driven by the Router. Backbone works with a Rails backend to provide inbox rendering, archiving, replying, composing, and even a changes feed. Using Backbone's event-driven model and pushing the rendering and interaction logic to the front-end has not only simplified the view code, it has also drastically reduced the load on Shortmail's servers.

## Battlefield Play4Free

Battlefield Play4Free is the latest free-to-play first person shooter from the same team that created Battlefield Heroes. The in-game HTML5 front-end for makes heavy use of Backbone's views, models and collections to help keep the code modular and structured.

## Salon.io

Salon.io provides a space where photographers, artists and designers freely arrange their visual art on virtual walls. Salon.io runs on Rails, but does not use much of the traditional stack, as the entire frontend is designed as a single page web app, using Backbone.js and CoffeeScript.

## TileMill

Our fellow Knight Foundation News Challenge winners, MapBox, created an open-source map design studio with Backbone.js: TileMill. TileMill lets you manage map layers based on shapefiles and rasters, and edit their appearance directly in the browser with the Carto styling language. Note that the gorgeous MapBox homepage is also a Backbone.js app.

## Blossom

Blossom is a lightweight project management tool for lean teams. Backbone.js is heavily used in combination with CoffeeScript to provide a smooth interaction experience. The RESTful backend is built with Flask on Google App Engine.

## Animoto

Animoto is a web-based video creation platform, where users can upload their own photos, video clips and music and create beautifully orchestrated slideshows. The video editor app is built with Backbone.js and jQuery and interfaces with a Ruby on Rails backend. Backbone has provided structure which helps the Animoto team iterate quickly on the codebase while reducing the risk of regressions.

## ChainCal

ChainCal is an iPhone app that helps you to track your daily goals in a minimalist, visual way. The app is written almost entirely in CoffeeScript, Backbone handles the models, collections and views, and persistence is done with a Backbone.sync localStorage adapter. Templates are written in Eco and the app is packaged with Brunch and deployed with Phonegap.

## AtticTV

AtticTV is MTV for the Youtube Generation: kick back and relax while watching the best music videos of your favorite genre. The videos are synced across the world, so, you're never watching alone on AtticTV. AtticTV is served by NodeJS written in CoffeeScript with Socket.IO as data transport. The frontend is built with Backbone.js with pushstate support, jQuery, and Jade templates.

## Decide

Decide.com helps people decide when to buy consumer electronics. It relies heavily on Backbone.js to render and update its Search Results Page. An "infinite scroll" feature takes advantage of a SearchResults model containing a collection of Product models to fetch more results and render them on the fly with Mustache. A SearchController keeps everything in sync and maintains page state in the URL. Backbone also powers the user accounts and settings management.

## Trello

Trello is a collaboration tool that organizes your projects into boards. A Trello board holds many lists of cards, which can contain checklists, files and conversations, and may be voted on and organized with labels. Updates on the board happen in real time. The site was built ground up using Backbone.js for all the models, views, and routes.

## Ducksboard

Ducksboard is an online dashboard for your SaaS and business metrics, built with Twisted and Django and using WebSockets. It can fetch data from popular providers or accept input through a simple API. Backbone is used throughout Ducksboard's interface, every widget, dashboard and SaaS account is a Backbone model with several views (data display, configuration view). A live demo is available.

## Picklive

Tim Ruffles and Tim Parker created the game client for Picklive, a real-time fantasy-soccer game. The client is written in CoffeeScript, organised into modules via require.js, tested with jsTestDriver and uses Mustache.js for templating. Backbone's model and sync layer separation manages the complexity of mixed polling and web-sockets based synchronisation.

## QuietWrite

James Yu used Backbone.js to create QuietWrite, an app that gives writers a clean and quiet interface to concentrate on the text itself. The editor relies on Backbone to persist document data to the server. He followed up with a Backbone.js + Rails tutorial that describes how to implement CloudEdit, a simple document editing app.

## Tzigla

Cristi Balan and Irina Dumitrascu created Tzigla, a collaborative drawing application where artists make tiles that connect to each other to create surreal drawings. Backbone models help organize the code, routers provide bookmarkable deep links, and the views are rendered with haml.js and Zepto. Tzigla is written in Ruby (Rails) on the backend, and CoffeeScript on the frontend, with Jammit prepackaging the static assets.

## F.A.Q.

Catalog of Events
Here's a list of all of the built-in events that Backbone.js can fire. You're also free to trigger your own events on Models and Views as you see fit.

- "add" (model, collection) — when a model is added to a collection.
- "remove" (model, collection) — when a model is removed from a collection.
- "reset" (collection) — when the collection's entire contents have been replaced.
- "change" (model, options) — when a model's attributes have changed.
- "change:[attribute]" (model, value, options) — when a specific attribute has been updated.
- "destroy" (model, collection) — when a model is destroyed.
- "sync" (model, collection) — triggers whenever a model has been successfully synced to the server.
- "error" (model, collection) — when a model's validation fails, or a save call fails on the server.
- "route:[name]" (router) — when one of a router's routes has matched.
- "all" — this special event fires for any triggered event, passing the event name as the first argument.

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();

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 overriden 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. With Backbone, when dealing with events and callbacks, you'll often find it useful to rely on _.bind and _.bindAll from Underscore.js.

When binding callbacks to Backbone events, you can choose to pass an optional third argument to specify the `this` that will be used when the callback is later invoked:

    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);
      }

    });

    // 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 adds 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.

## Change Log

0.9.2 — March 21, 2012 — Diff

- Instead of throwing an error when adding duplicate models to a collection, Backbone will now silently skip them instead.
- Added push, pop, unshift, and shift to collections.
- A model's changed hash is now exposed for easy reading of the changed attribute delta, since the model's last `"change"` event.
- Added where to collections for simple filtering.
- You can now use a single off call to remove all callbacks bound to a specific object.
- Bug fixes for nested individual change events, some of which may be "silent".
- Bug fixes for URL encoding in `location.hash` fragments.
- Bug fix for client-side validation in advance of a `save` call with `{wait: true}`.
- Updated / refreshed the example Todo List app.

0.9.1 — Feb. 2, 2012 — Diff

- Reverted to 0.5.3-esque behavior for validating models. Silent changes no longer trigger validation (making it easier to work with forms). Added an `isValid` function that you can use to check if a model is currently in a valid state.
- If you have multiple versions of jQuery on the page, you can now tell Backbone which one to use with `Backbone.setDomLibrary`.
- Fixes regressions in 0.9.0 for routing with "root", saving with both "wait" and "validate", and the order of nested "change" events.

0.9.0 — Jan. 30, 2012 — Diff

- Creating and destroying models with `create` and `destroy` are now optimistic by default. Pass `{wait: true}` as an option if you'd like them to wait for a successful server response to proceed.
- Two new properties on views: `$el` — a cached jQuery (or Zepto) reference to the view's element, and `setElement`, which should be used instead of manually setting a view's `el`. It will both set `view.el` and `view.$el` correctly, as well as re-delegating events on the new DOM element.
- You can now bind and trigger multiple spaced-delimited events at once. For example: `model.on("change:name change:age", ...)`
- When you don't know the key in advance, you may now call `model.set(key, value)` as well as `save`.
- Multiple models with the same `id` are no longer allowed in a single collection.
- Added a `"sync"` event, which triggers whenever a model's state has been successfully synced with the server (create, save, destroy).
- `bind` and `unbind` have been renamed to `on` and `off` for clarity, following jQuery's lead. The old names are also still supported.
- A Backbone collection's `comparator` function may now behave either like a sortBy (pass a function that takes a single argument), or like a sort (pass a comparator function that expects two arguments). The comparator function is also now bound by default to the collection — so you can refer to `this` within it.
- A view's `events` hash may now also contain direct function values as well as the string names of existing view methods.
- Validation has gotten an overhaul — a model's `validate` function will now be run even for silent changes, and you can no longer create a model in an initially invalid state.
- Added `shuffle` and `initial` to collections, proxied from Underscore.
- `Model#urlRoot` may now be defined as a function as well as a value.
- `View#attributes` may now be defined as a function as well as a value.
- Calling `fetch` on a collection will now cause all fetched JSON to be run through the collection's model's `parse` function, if one is defined.
- You may now tell a router to `navigate(fragment, {replace: true})`, which will either use `history.replaceState` or `location.hash.replace`, in order to change the URL without adding a history entry.
- Within a collection's `add` and `remove` events, the index of the model being added or removed is now available as `options.index`.
- Added an `undelegateEvents` to views, allowing you to manually remove all configured event delegations.
- Although you shouldn't be writing your routes with them in any case — leading slashes (`/`) are now stripped from routes.
- Calling `clone` on a model now only passes the attributes for duplication, not a reference to the model itself.

0.5.3 — August 9, 2011
A View's `events` property may now be defined as a function, as well as an object literal, making it easier to programmatically define and inherit events. `groupBy` is now proxied from Underscore as a method on Collections. If the server has already rendered everything on page load, pass `Backbone.history.start({silent: true})` to prevent the initial route from triggering. Bugfix for pushState with encoded URLs.

0.5.2 — July 26, 2011
The `bind` function, can now take an optional third argument, to specify the `this` of the callback function. Multiple models with the same `id` are now allowed in a collection. Fixed a bug where calling `.fetch(jQueryOptions)` could cause an incorrect URL to be serialized. Fixed a brief extra route fire before redirect, when degrading from `pushState`.

0.5.1 — July 5, 2011
Cleanups from the 0.5.0 release, to wit: improved transparent upgrades from hash-based URLs to pushState, and vice-versa. Fixed inconsistency with non-modified attributes being passed to `Model#initialize`. Reverted a 0.5.0 change that would strip leading hashbangs from routes. Added `contains` as an alias for `includes`.

0.5.0 — July 1, 2011
A large number of tiny tweaks and micro bugfixes, best viewed by looking at the commit diff. HTML5 `pushState` support, enabled by opting-in with: `Backbone.history.start({pushState: true})`. `Controller` was renamed to `Router`, for clarity. `Collection#refresh` was renamed to `Collection#reset` to emphasize its ability to both reset the collection with new models, as well as empty out the collection when used with no parameters. `saveLocation` was replaced with `navigate`. RESTful persistence methods (save, fetch, etc.) now return the jQuery deferred object for further success/error chaining and general convenience. Improved XSS escaping for `Model#escape`. Added a `urlRoot` option to allow specifying RESTful urls without the use of a collection. An error is thrown if `Backbone.history.start` is called multiple times. `Collection#create` now validates before initializing the new model. `view.el` can now be a jQuery string lookup. Backbone Views can now also take an `attributes` parameter. `Model#defaults` can now be a function as well as a literal attributes object.

0.3.3 — Dec 1, 2010
Backbone.js now supports Zepto, alongside jQuery, as a framework for DOM manipulation and Ajax support. Implemented Model#escape, to efficiently handle attributes intended for HTML interpolation. When trying to persist a model, failed requests will now trigger an `"error"` event. The ubiquitous `options` argument is now passed as the final argument to all `"change"` events.

0.3.2 — Nov 23, 2010
Bugfix for IE7 + iframe-based "hashchange" events. `sync` may now be overridden on a per-model, or per-collection basis. Fixed recursion error when calling `save` with no changed attributes, within a `"change"` event.

0.3.1 — Nov 15, 2010
All `"add"` and `"remove"` events are now sent through the model, so that views can listen for them without having to know about the collection. Added a `remove` method to Backbone.View. `toJSON` is no longer called at all for `'read'` and `'delete'` requests. Backbone routes are now able to load empty URL fragments.

0.3.0 — Nov 9, 2010
Backbone now has Controllers and History, for doing client-side routing based on URL fragments. Added `emulateHTTP` to provide support for legacy servers that don't do `PUT` and `DELETE`. Added `emulateJSON` for servers that can't accept `application/json` encoded requests. Added Model#clear, which removes all attributes from a model. All Backbone classes may now be seamlessly inherited by CoffeeScript classes.

0.2.0 — Oct 25, 2010
Instead of requiring server responses to be namespaced under a `model` key, now you can define your own parse method to convert responses into attributes for Models and Collections. The old `handleEvents` function is now named delegateEvents, and is automatically called as part of the View's constructor. Added a toJSON function to Collections. Added Underscore's chain to Collections.

0.1.2 — Oct 19, 2010
Added a Model#fetch method for refreshing the attributes of single model from the server. An `error` callback may now be passed to `set` and `save` as an option, which will be invoked if validation fails, overriding the `"error"` event. You can now tell backbone to use the `_method` hack instead of HTTP methods by setting `Backbone.emulateHTTP = true`. Existing Model and Collection data is no longer sent up unnecessarily with `GET` and `DELETE` requests. Added a `rake lint` task. Backbone is now published as an NPM module.

0.1.1 — Oct 14, 2010
Added a convention for `initialize` functions to be called upon instance construction, if defined. Documentation tweaks.

0.1.0 — Oct 13, 2010
Initial Backbone release.