source :: http://backbonejs.org/
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 examples that follow are runnable. Click the
play button
to execute them.
Upgrading to 1.1
Backbone
1.1 should be a fairly painless upgrade from the
0.9.X
series. If you're upgrading from an older version, be sure to check out the
change log. In brief, a few of the larger breaking
changes are:
-
If you want to smartly update the contents of a Collection,
adding new models, removing missing ones, and merging those already present,
you now call set (previously named "update"),
a similar operation to calling set on a Model. This is now the
default when you call fetch on a collection.
To get the old behavior, pass {reset: true}.
-
If you have characters in your URL segments that require URL encoding,
Backbone will now decode them for you (normalizing the behavior
cross-browser) before your route handlers receive them as arguments.
-
In 0.9.x, Backbone events gained two new methods:
listenTo and
stopListening, which make it easier
to create Views that have all of their observers unbound when you
want to remove the view.
-
Model validation is now only enforced by default in
save — not in
set unless the {validate:true}
option is passed. Model validation now fires an "invalid" event instead of
"error".
-
In 1.1, Backbone Views no longer have the options argument
attached as this.options automatically. Feel free to continue
attaching it if you like.
-
In 1.1, The Collection methods add, remove,
set, push, and shift now return the model
(or models) added or removed from the collection.
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)
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);
});
All Backbone event methods also support an event map syntax, as an alternative
to positional arguments:
book.on({
"change:title": titleView.update,
"change:author": authorPane.update,
"destroy": bookView.remove
});
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.
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.
object.once(event, callback, [context])
Just like
on, but causes the bound callback to only
fire once before being removed. Handy for saying "the next time that X happens, do this".
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);
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);
object.listenToOnce(other, event, callback)
Just like
listenTo, but causes the bound
callback to only fire once before being removed.
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.
- "reset" (collection, options) — when the collection's entire contents have been replaced.
- "sort" (collection, options) — when the collection has been re-sorted.
- "change" (model, options) — when a model's attributes have changed.
- "change:[attribute]" (model, value, options) — when a specific attribute has been updated.
- "destroy" (model, collection, options) — when a model is destroyed.
- "request" (model_or_collection, xhr, options) — when a model or collection has started a request to the server.
- "sync" (model_or_collection, resp, options) — when a model or collection has been successfully synced with the server.
- "error" (model_or_collection, resp, options) — when model's or collection's request to remote server has failed.
- "invalid" (model, error, options) — when a model's validation fails on the client.
- "route:[name]" (params) — Fired by the router when a specific route is matched.
- "route" (route, params) — Fired by the router when any route has been matched.
- "route" (router, route, params) — Fired by history when any route has been matched.
- "all" — this special event fires for any triggered event, passing the event name as the first argument.
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();
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);
...
}
});
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.
model.get(attribute)
Get the current value of an attribute from the model. For example:
note.get("title")
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");
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'));
model.has(attribute)
Returns true if the attribute is set to a non-null or non-undefined
value.
if (note.has("title")) {
...
}
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.
model.clear([options])
Removes all attributes from the model, including the id attribute. Fires a "change" event unless
silent is passed as an option.
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.
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);
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.
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.
model.changed
The
changed property is the internal hash containing all the attributes
that have changed since the 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.
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.
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));
model.sync(method, model, [options])
Uses
Backbone.sync to persist the state of a model to
the server. Can be overridden for custom behavior.
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 both passed
(model, response, options) as arguments.
// Poll every 10 seconds to keep the channel model up-to-date.
setInterval(function() {
channel.fetch();
}, 10000);
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(){ ... }});
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) {
...
}});
Backbone proxies to Underscore.js to provide 6 object functions
on Backbone.Model. They aren't all documented here, but
you can take a look at the Underscore documentation for the full details…
user.pick('first_name', 'last_name', 'email');
chapters.keys().join(', ');
model.validate(attributes, options)
This method is left undefined, and you're encouraged to override it with
your custom validation logic, if you have any that can be performed
in JavaScript. By default validate is called before
save, but can also be called before set if
{validate:true} is passed. The validate method is passed
the model attributes, as well as the options from set or save.
If the attributes are valid, don't return anything from validate;
if they are invalid, return an error of your choosing. It
can be as simple as a string error message to be displayed, or a complete
error object that describes the error programmatically. If validate
returns an error, save will not continue, and the
model attributes will not be modified on the server.
Failed validations trigger an "invalid" event, and set the
validationError property on the model with the value returned by
this method.
var Chapter = Backbone.Model.extend({
validate: function(attrs, options) {
if (attrs.end < attrs.start) {
return "can't end before it starts";
}
}
});
var one = new Chapter({
title : "Chapter One: The Beginning"
});
one.on("invalid", function(model, error) {
alert(model.get("title") + " " + error);
});
one.save({
start: 15,
end: 10
});
"invalid" events are useful for providing coarse-grained error
messages at the model or collection level.
model.validationError
The value returned by
validate during the last failed validation.
model.isValid()
Run
validate to check the model state.
var Chapter = Backbone.Model.extend({
validate: function(attrs, options) {
if (attrs.end < attrs.start) {
return "can't end before it starts";
}
}
});
var one = new Chapter({
title : "Chapter One: The Beginning"
});
one.set({
start: 15,
end: 10
});
if (!one.isValid()) {
alert(one.get("title") + " " + one.validationError);
}
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"
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());
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
model.clone()
Returns a new instance of the model with identical attributes.
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.
model.hasChanged([attribute])
Has the model changed since the 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")) {
...
}
});
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.
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"});
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", ...)
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.
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
});
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);
}
}
});
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.
var tabs = new TabSet([tab1, tab2, tab3]);
var spaces = new Backbone.Collection([], {
model: Space
});
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.
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));
collection.sync(method, collection, [options])
Uses
Backbone.sync to persist the state of a
collection to the server. Can be overridden for custom behavior.
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…
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();
});
collection.add(models, [options])
Add a model (or an array of models) to the collection, firing an
"add"
event. If a
model property is defined, you may also pass
raw attributes objects, and have them be vivified as instances of the model.
Returns the added (or preexisting, if duplicate) models.
Pass
{at: index} to splice the model into the collection at the
specified
index. If you're adding models to the collection that are
already in the collection, they'll be ignored, unless you pass
{merge: true}, in which case their attributes will be merged
into the corresponding models, firing any appropriate
"change" events.
var ships = new Backbone.Collection;
ships.on("add", function(ship) {
alert("Ahoy " + ship.get("name") + "!");
});
ships.add([
{name: "Flying Dutchman"},
{name: "Black Pearl"}
]);
Note that adding the same model (a model with the same id) to
a collection more than once
is a no-op.
collection.remove(models, [options])
Remove a model (or an array of models) from the collection, and returns them.
Fires a "remove" event, which you can use silent to suppress.
The model's index before removal is available to listeners as
options.index.
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. Returns the newly-set models.
For convenience, within a "reset" event, the list of any
previous models is available as options.previousModels.
Here's an example using
reset to bootstrap a collection during initial page load,
in a Rails application:
<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.
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. Returns the touched models in the collection.
If you'd like to customize the behavior, you can disable
it with options: {add: false}, {remove: false}, or {merge: false}.
var vanHalen = new Backbone.Collection([eddie, alex, stone, roth]);
vanHalen.set([eddie, alex, stone, hagar]);
// Fires a "remove" event for roth, and an "add" event for "hagar".
// Updates any of stone, alex, and eddie's attributes that may have
// changed over the years.
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);
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.
collection.push(model, [options])
Add a model at the end of a collection. Takes the same options as
add.
collection.pop([options])
Remove and return the last model from a collection. Takes the same options as
remove.
collection.unshift(model, [options])
Add a model at the beginning of a collection. Takes the same options as
add.
collection.shift([options])
Remove and return the first model from a collection. Takes the same options as
remove.
collection.slice(begin, end)
Return a shallow copy of this collection's models, using the same options as
native
Array#slice.
collection.length
Like an array, a Collection maintains a length property, counting
the number of models it contains.
collection.comparator
By default there is no
comparator for a collection.
If you define a comparator, it will be used to maintain
the collection in sorted order. This means that as models are added,
they are inserted at the correct index in
collection.models.
A comparator can be defined as a
sortBy
(pass a function that takes a single argument),
as a
sort
(pass a comparator function that expects two arguments),
or as a string indicating the attribute to sort by.
"sortBy" comparator functions take a model and return a numeric or string
value by which the model should be ordered relative to others.
"sort" comparator functions take two models, and return
-1 if
the first model should come before the second,
0 if they are of
the same rank and
1 if the first model should come after.
Note 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.
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
will sort itself 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.
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));
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);
collection.findWhere(attributes)
Just like
where, but directly returns only
the first model in the collection that matches the passed
attributes.
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';
}
});
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;
}
});
collection.clone()
Returns a new instance of the collection with an identical list of models.
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.
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 or an
existing, unsaved model object.
Creating a model will cause an immediate
"add" event to be
triggered on the collection, a
"request" event as the new model is
sent to the server, as well as a
"sync" event, once the
server has responded with the successful creation of the model. Pass
{wait: true}
if you'd like to wait for the server before adding the new model to the collection.
var Library = Backbone.Collection.extend({
model: Book
});
var nypl = new Library;
var othello = nypl.create({
title: "Othello",
author: "William Shakespeare"
});
Backbone.Router
Web applications often provide linkable, bookmarkable, shareable URLs for
important locations in the app. Until recently, hash fragments
(
#page) were used to provide these permalinks, but with the
arrival of the History API, it's now possible to use standard URLs (
/page).
Backbone.Router provides methods for routing client-side pages, and
connecting them to actions and events. For browsers which don't yet support
the History API, the Router handles graceful fallback and transparent
translation to the fragment version of the URL.
During page load, after your application has finished creating all of its routers,
be sure to call
Backbone.history.start(), or
Backbone.history.start({pushState: true}) to route the initial URL.
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) {
...
}
});
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.
A route of
"file/*path" will match
#file/nested/folder/file.txt, passing
"nested/folder/file.txt" to the action.
A route of
"docs/:section(/:subsection)" will match
#docs/faq and
#docs/faq/installing, passing
"faq" to the action in the first case, and passing
"faq"
and
"installing" to the action in the second.
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) {
...
});
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.
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) { ... }
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});
router.execute(callback, args)
This method is called internally within the router, whenever a route
matches and its corresponding callback is about to be executed.
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) {
args.push(parseQueryString(args.pop()));
if (callback) callback.apply(this, args);
}
});
Backbone.history
History serves as a global router (per frame) to handle
hashchange
events or
pushState, match the appropriate route, and trigger callbacks.
You shouldn't ever have to create one of these yourself since
Backbone.history
already contains one.
pushState support exists on a purely opt-in basis in Backbone.
Older browsers that don't support
pushState will continue to use
hash-based URL fragments, and if a hash URL is visited by a
pushState-capable browser, it will be transparently upgraded to
the true URL. Note that using real URLs requires your web server to be
able to correctly render those pages, so back-end changes are required
as well. For example, if you have a route of
/documents/100,
your web server must be able to serve that page, if the browser
visits that URL directly. For full search-engine crawlability, it's best to
have the server generate the complete HTML for the page ... but if it's a web
application, just rendering the same content you would have for the root URL,
and filling in the rest with Backbone Views and JavaScript works fine.
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/"})
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.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 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
- patch → PATCH /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 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
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.
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.
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.
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.
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
});
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);
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);
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 $el reference
and move the view's delegated events from the old element to the new one.
view.attributes
A hash of attributes that will be set as HTML DOM element attributes on the
view's el (id, class, data-properties, etc.), or a function that
returns such a hash.
view.$(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()
};
}
});
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(...)
});
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.
view.remove()
Removes a view from the DOM, and calls
stopListening to remove any bound
events that the view has
listenTo'd.
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 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()
Removes all of the view's delegated events. Useful if you want to disable
or remove a view from the DOM temporarily.
Utility
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.$ = $;
If you have multiple copies of jQuery on the page, or simply want
to tell Backbone to use a particular object as its DOM / Ajax library,
this is the property for you. If you're loading Backbone with CommonJS
(e.g. node, component, or browserify) you must set this property manually.
var Backbone.$ = require('jquery');
F.A.Q.
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.
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.
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.
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.
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.
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.
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);
messages.each(this.addMessage, this);
}
});
// Later, in the app...
Inbox.messages.add(newMessage);
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. If you've
worked on an app that uses Backbone, please add it to the
wiki page of Backbone apps.
, then Create new.
