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<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<meta name="generator" content="pandoc">
<title>Developing Backbone.js Applications - </title>
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<p>
<h1>Developing Backbone.js Applications</h1>
<h3>By Addy Osmani <a href="http://twitter.com/addyosmani">@addyosmani</a></h3>
</p>
<div style="width:500px">
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<p> <br></p>
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<p><img src="img/oreilly.jpg"/></p>
<a href="http://shop.oreilly.com/product/0636920025344/ReviewSubmit.do?sortby=publicationDate?pageId=0636920025344.IP"><img style="position: absolute; top: 0; right: 0; border: 0;" src="http://addyosmani.github.com/backbone-fundamentals/img/helpful.png" alt="Was this helpful? We'd love you to write a review."></a>
<nav id="TOC">
<ul>
<li><a href="#prelude">Prelude</a></li>
<li><a href="#target-audience">Target Audience</a></li>
<li><a href="#acknowledgements">Acknowledgements</a></li>
<li><a href="#credits">Credits</a></li>
<li><a href="#reading">Reading</a></li>
<li><a href="#introduction">Introduction</a><ul>
<li><a href="#what-is-mvc">What Is MVC?</a></li>
<li><a href="#what-is-backbone.js">What is Backbone.js?</a></li>
<li><a href="#when-do-i-need-a-javascript-mvc-framework">When Do I Need A JavaScript MVC Framework?</a></li>
<li><a href="#why-consider-backbone.js">Why Consider Backbone.js?</a></li>
<li><a href="#setting-expectations">Setting Expectations</a></li>
</ul></li>
<li><a href="#fundamentals">Fundamentals</a><ul>
<li><a href="#mvc">MVC</a><ul>
<li><a href="#smalltalk-80-mvc">Smalltalk-80 MVC</a></li>
<li><a href="#mvc-applied-to-the-web">MVC Applied To The Web</a></li>
<li><a href="#client-side-mvc-single-page-apps">Client-Side MVC & Single Page Apps</a></li>
<li><a href="#client-side-mvc---backbone-style">Client-Side MVC - Backbone Style</a></li>
<li><a href="#implementation-specifics">Implementation Specifics</a><ul>
<li><a href="#models">Models</a></li>
<li><a href="#views">Views</a></li>
<li><a href="#controllers">Controllers</a></li>
</ul></li>
</ul></li>
<li><a href="#what-does-mvc-give-us">What does MVC give us?</a><ul>
<li><a href="#delving-deeper-into-mvc">Delving Deeper into MVC</a></li>
<li><a href="#summary">Summary</a></li>
<li><a href="#further-reading">Further reading</a></li>
</ul></li>
<li><a href="#fast-facts">Fast facts</a><ul>
<li><a href="#backbone.js">Backbone.js</a></li>
<li><a href="#used-by">Used by</a></li>
</ul></li>
</ul></li>
<li><a href="#backbone-basics">Backbone Basics</a><ul>
<li><a href="#getting-setup">Getting setup</a></li>
<li><a href="#models-1">Models</a><ul>
<li><a href="#initialization">Initialization</a></li>
<li><a href="#getters-setters">Getters & Setters</a></li>
<li><a href="#listening-for-changes-to-your-model">Listening for changes to your model</a></li>
<li><a href="#validation">Validation</a></li>
</ul></li>
<li><a href="#views-1">Views</a><ul>
<li><a href="#creating-new-views">Creating new views</a></li>
<li><a href="#what-is-el">What is <code>el</code>?</a></li>
</ul></li>
<li><a href="#collections">Collections</a><ul>
<li><a href="#adding-and-removing-models">Adding and Removing Models</a></li>
<li><a href="#retrieving-models">Retrieving Models</a></li>
<li><a href="#listening-for-events">Listening for events</a></li>
<li><a href="#resettingrefreshing-collections">Resetting/Refreshing Collections</a></li>
<li><a href="#underscore-utility-functions">Underscore utility functions</a></li>
<li><a href="#chainable-api">Chainable API</a></li>
</ul></li>
<li><a href="#restful-persistence">RESTful Persistence</a></li>
<li><a href="#events">Events</a><ul>
<li><a href="#on-off-and-trigger">on(), off(), and trigger()</a></li>
<li><a href="#listento-and-stoplistening">listenTo() and stopListening()</a></li>
<li><a href="#events-and-views">Events and Views</a></li>
</ul></li>
<li><a href="#routers">Routers</a><ul>
<li><a href="#backbone.history">Backbone.history</a></li>
</ul></li>
<li><a href="#backbones-sync-api">Backbone’s Sync API</a></li>
<li><a href="#dependencies">Dependencies</a></li>
<li><a href="#summary-1">Summary</a></li>
</ul></li>
<li><a href="#exercise-1-todos---your-first-backbone.js-app">Exercise 1: Todos - Your First Backbone.js App</a><ul>
<li><a href="#static-html">Static HTML</a><ul>
<li><a href="#header-and-scripts">Header and Scripts</a></li>
<li><a href="#application-html">Application HTML</a></li>
<li><a href="#templates">Templates</a></li>
</ul></li>
<li><a href="#todo-model">Todo model</a></li>
<li><a href="#todo-collection">Todo collection</a></li>
<li><a href="#application-view">Application View</a></li>
<li><a href="#individual-todo-view">Individual Todo View</a></li>
<li><a href="#startup">Startup</a></li>
<li><a href="#in-action">In action</a></li>
<li><a href="#completing-deleting-todos">Completing & deleting todos</a></li>
<li><a href="#todo-routing">Todo routing</a></li>
<li><a href="#summary-2">Summary</a></li>
</ul></li>
<li><a href="#exercise-2-book-library---your-first-restful-backbone.js-app">Exercise 2: Book Library - Your First RESTful Backbone.js App</a><ul>
<li><a href="#setting-up">Setting up</a><ul>
<li><a href="#creating-the-model-collection-views-and-app">Creating the Model, Collection, Views, and App</a></li>
</ul></li>
<li><a href="#wiring-in-the-interface">Wiring in the interface</a><ul>
<li><a href="#adding-models">Adding models</a></li>
<li><a href="#removing-models">Removing models</a></li>
</ul></li>
<li><a href="#creating-the-back-end">Creating the back-end</a><ul>
<li><a href="#install-node.js-npm-and-mongodb">Install node.js, npm, and MongoDB</a></li>
<li><a href="#install-node-modules">Install node modules</a></li>
<li><a href="#create-a-simple-web-server">Create a simple web server</a></li>
<li><a href="#connect-to-the-database">Connect to the database</a></li>
</ul></li>
<li><a href="#talking-to-the-server">Talking to the server</a><ul>
<li><a href="#summary-3">Summary</a></li>
</ul></li>
</ul></li>
<li><a href="#backbone-extensions">Backbone Extensions</a><ul>
<li><a href="#marionettejs-backbone.marionette">MarionetteJS (Backbone.Marionette)</a><ul>
<li><a href="#boilerplate-rendering-code">Boilerplate Rendering Code</a></li>
<li><a href="#reducing-boilerplate-with-marionette.itemview">Reducing Boilerplate With Marionette.ItemView</a></li>
<li><a href="#memory-management">Memory Management</a></li>
<li><a href="#region-management">Region Management</a></li>
<li><a href="#marionette-todo-app">Marionette Todo app</a><ul>
<li><a href="#controllers-1">Controllers</a></li>
<li><a href="#compositeview">CompositeView</a></li>
</ul></li>
<li><a href="#is-the-marionette-implementation-of-the-todo-app-more-maintainable">Is the Marionette implementation of the Todo app more maintainable?</a></li>
<li><a href="#marionette-and-flexibility">Marionette And Flexibility</a></li>
<li><a href="#and-so-much-more">And So Much More</a></li>
</ul></li>
<li><a href="#thorax">Thorax</a><ul>
<li><a href="#hello-world">Hello World</a></li>
<li><a href="#embedding-child-views">Embedding child views</a></li>
<li><a href="#view-helpers">View helpers</a></li>
<li><a href="#collection-helper">collection helper</a></li>
<li><a href="#custom-html-data-attributes">Custom HTML data attributes</a></li>
<li><a href="#thorax-resources">Thorax Resources</a></li>
</ul></li>
</ul></li>
<li><a href="#common-problems-solutions">Common Problems & Solutions</a><ul>
<li><a href="#working-with-nested-views">Working With Nested Views</a></li>
<li><a href="#managing-models-in-nested-views">Managing Models In Nested Views</a></li>
<li><a href="#rendering-a-parent-view-from-a-child-view">Rendering A Parent View From A Child View</a></li>
<li><a href="#disposing-view-hierarchies">Disposing View Hierarchies</a></li>
<li><a href="#rendering-view-hierarchies">Rendering View Hierarchies</a></li>
<li><a href="#working-with-nested-models-or-collections">Working With Nested Models Or Collections</a></li>
<li><a href="#better-model-property-validation">Better Model Property Validation</a><ul>
<li><a href="#backbone.validateall">Backbone.validateAll</a></li>
<li><a href="#backbone.validation">Backbone.Validation</a></li>
<li><a href="#form-specific-validation-classes">Form-specific validation classes</a></li>
</ul></li>
<li><a href="#avoiding-conflicts-with-multiple-backbone-versions">Avoiding Conflicts With Multiple Backbone Versions</a></li>
<li><a href="#building-model-and-view-hierarchies">Building Model And View Hierarchies</a></li>
<li><a href="#event-aggregators-and-mediators">Event Aggregators And Mediators</a><ul>
<li><a href="#event-aggregator">Event Aggregator</a><ul>
<li><a href="#backbones-event-aggregator">Backbone’s Event Aggregator</a><ul>
<li><a href="#jquerys-event-aggregator">jQuery’s Event Aggregator</a></li>
</ul></li>
</ul></li>
<li><a href="#mediator">Mediator</a></li>
<li><a href="#similarities-and-differences">Similarities And Differences</a><ul>
<li><a href="#events-1">Events</a></li>
<li><a href="#third-party-objects">Third-Party Objects</a></li>
</ul></li>
<li><a href="#relationships-when-to-use-which">Relationships: When To Use Which</a><ul>
<li><a href="#event-aggregator-use">Event Aggregator Use</a></li>
<li><a href="#mediator-use">Mediator Use</a></li>
</ul></li>
<li><a href="#event-aggregator-and-mediator-together">Event Aggregator And Mediator Together</a></li>
<li><a href="#pattern-language-semantics">Pattern Language: Semantics</a></li>
</ul></li>
</ul></li>
<li><a href="#modular-development">Modular Development</a><ul>
<li><a href="#introduction-1">Introduction</a></li>
<li><a href="#organizing-modules-with-requirejs-and-amd">Organizing modules with RequireJS and AMD</a><ul>
<li><a href="#maintainability-problems-with-multiple-script-files">Maintainability problems with multiple script files</a></li>
<li><a href="#need-for-better-dependency-management">Need for better dependency management</a></li>
<li><a href="#asynchronous-module-definition-amd">Asynchronous Module Definition (AMD)</a></li>
<li><a href="#writing-amd-modules-with-requirejs">Writing AMD modules with RequireJS</a><ul>
<li><a href="#alternate-syntax">Alternate syntax</a></li>
</ul></li>
<li><a href="#getting-started-with-requirejs">Getting Started with RequireJS</a><ul>
<li><a href="#requirejs-configuration">RequireJS Configuration</a><ul>
<li><a href="#requirejs-shims">RequireJS Shims</a></li>
</ul></li>
<li><a href="#custom-paths">Custom Paths</a></li>
</ul></li>
<li><a href="#require.js-and-backbone-examples">Require.js and Backbone Examples</a><ul>
<li><a href="#wrapping-models-views-and-other-components-with-amd">Wrapping models, views, and other components with AMD</a></li>
</ul></li>
<li><a href="#keeping-your-templates-external-using-requirejs-and-the-text-plugin">Keeping Your Templates External Using RequireJS And The Text Plugin</a></li>
<li><a href="#optimizing-backbone-apps-for-production-with-the-requirejs-optimizer">Optimizing Backbone apps for production with the RequireJS Optimizer</a></li>
</ul></li>
</ul></li>
<li><a href="#exercise-your-first-modular-backbone-requirejs-app">Exercise: Your First Modular Backbone + RequireJS App</a><ul>
<li><a href="#overview">Overview</a></li>
<li><a href="#markup">Markup</a></li>
<li><a href="#configuration-options">Configuration options</a></li>
<li><a href="#modularizing-our-models-views-and-collections">Modularizing our models, views and collections</a></li>
<li><a href="#route-based-module-loading">Route-based module loading</a><ul>
<li><a href="#json-based-module-configuration">JSON-based module configuration</a></li>
<li><a href="#module-loader-router">Module loader Router</a></li>
<li><a href="#using-nodejs-to-handle-pushstate">Using NodeJS to handle pushState</a></li>
</ul></li>
<li><a href="#an-asset-package-alternative-for-dependency-management">An asset package alternative for dependency management</a></li>
</ul></li>
<li><a href="#paginating-backbone.js-requests-collections">Paginating Backbone.js Requests & Collections</a><ul>
<li><a href="#paginators-pieces">Paginator’s pieces</a></li>
<li><a href="#live-examples">Live Examples</a></li>
<li><a href="#paginator.requestpager">Paginator.requestPager</a><ul>
<li><a href="#create-a-new-paginated-collection">1. Create a new Paginated collection</a></li>
<li><a href="#set-the-model-for-the-collection-as-normal">2: Set the model for the collection as normal</a></li>
<li><a href="#configure-the-base-url-and-the-type-of-the-request">3. Configure the base URL and the type of the request</a></li>
<li><a href="#configure-how-the-library-will-show-the-results">4. Configure how the library will show the results</a></li>
<li><a href="#configure-the-parameters-we-want-to-send-to-the-server">5. Configure the parameters we want to send to the server</a></li>
<li><a href="#finally-configure-collection.parse-and-were-done">6. Finally, configure Collection.parse() and we’re done</a></li>
<li><a href="#convenience-methods">Convenience methods:</a></li>
</ul></li>
<li><a href="#paginator.clientpager">Paginator.clientPager</a><ul>
<li><a href="#create-a-new-paginated-collection-with-a-model-and-url">1. Create a new paginated collection with a model and URL</a></li>
<li><a href="#configure-the-base-url-and-the-type-of-the-request-1">2. Configure the base URL and the type of the request</a></li>
<li><a href="#configure-how-the-library-will-show-the-results-1">3. Configure how the library will show the results</a></li>
<li><a href="#configure-the-parameters-we-want-to-send-to-the-server-1">4. Configure the parameters we want to send to the server</a></li>
<li><a href="#finally-configure-collection.parse-and-were-done-1">5. Finally, configure Collection.parse() and we’re done</a></li>
<li><a href="#convenience-methods-1">Convenience methods:</a></li>
<li><a href="#implementation-notes">Implementation notes:</a></li>
</ul></li>
<li><a href="#plugins">Plugins</a></li>
</ul></li>
<li><a href="#backbone-boilerplate-and-grunt-bbb">Backbone Boilerplate And Grunt-BBB</a><ul>
<li><a href="#getting-started">Getting Started</a><ul>
<li><a href="#backbone-boilerplate-and-grunt-bbb-1">Backbone Boilerplate and Grunt-BBB</a></li>
</ul></li>
<li><a href="#creating-a-new-project">Creating a new project</a><ul>
<li><a href="#index.html">index.html</a></li>
<li><a href="#config.js">config.js</a></li>
<li><a href="#main.js">main.js</a></li>
<li><a href="#app.js">app.js</a></li>
<li><a href="#creating-backbone-boilerplate-modules">Creating Backbone Boilerplate Modules</a></li>
<li><a href="#router.js">router.js</a></li>
</ul></li>
<li><a href="#other-useful-tools-projects">Other Useful Tools & Projects</a><ul>
<li><a href="#yeoman">Yeoman</a></li>
<li><a href="#backbone-devtools">Backbone DevTools</a></li>
</ul></li>
<li><a href="#conclusions">Conclusions</a></li>
</ul></li>
<li><a href="#backbone-jquery-mobile">Backbone & jQuery Mobile</a><ul>
<li><a href="#mobile-app-development-with-jquery-mobile">Mobile app development with jQuery Mobile</a><ul>
<li><a href="#the-principle-of-progressive-widget-enhancement-by-jqmobile">The Principle of progressive widget enhancement by jQMobile</a></li>
</ul></li>
<li><a href="#basic-backbone-app-setup-for-jquery-mobile">Basic Backbone app setup for jQuery Mobile</a></li>
<li><a href="#the-workflow-with-backbone-and-jquerymobile">The workflow with Backbone and jQueryMobile</a><ul>
<li><a href="#routing-to-a-concrete-view-page-inherited-by-basicview">Routing to a concrete View-page, inherited by BasicView</a></li>
<li><a href="#management-of-mobile-page-templates">Management of mobile page templates</a></li>
<li><a href="#dom-management-and-.mobile.changepage">DOM management and $.mobile.changePage</a></li>
</ul></li>
<li><a href="#applying-advanced-jqm-techniques-to-backbone">Applying advanced jQM techniques to Backbone</a><ul>
<li><a href="#dynamic-dom-scripting">Dynamic DOM Scripting</a></li>
<li><a href="#intercept-jquery-mobile-events">Intercept jQuery Mobile events</a></li>
<li><a href="#performance">Performance</a></li>
<li><a href="#clever-multi-platform-support-management-by-dry">Clever multi platform support management by DRY</a></li>
</ul></li>
</ul></li>
<li><a href="#unit-testing">Unit Testing</a></li>
<li><a href="#jasmine">Jasmine</a><ul>
<li><a href="#behavior-driven-development">Behavior-Driven Development</a></li>
<li><a href="#suites-specs-spies">Suites, Specs, & Spies</a></li>
<li><a href="#beforeeach-and-aftereach">beforeEach() and afterEach()</a></li>
<li><a href="#shared-scope">Shared scope</a></li>
<li><a href="#getting-set-up">Getting set up</a></li>
<li><a href="#tdd-with-backbone">TDD With Backbone</a></li>
<li><a href="#models-2">Models</a></li>
<li><a href="#collections-1">Collections</a></li>
<li><a href="#views-2">Views</a><ul>
<li><a href="#view-testing">View testing</a><ul>
<li><a href="#initial-setup">Initial setup</a></li>
<li><a href="#view-rendering">View rendering</a></li>
<li><a href="#rendering-with-a-templating-system">Rendering with a templating system</a></li>
</ul></li>
</ul></li>
<li><a href="#conclusions-1">Conclusions</a></li>
<li><a href="#exercise">Exercise</a></li>
<li><a href="#further-reading-1">Further reading</a></li>
</ul></li>
<li><a href="#qunit">QUnit</a><ul>
<li><a href="#introduction-2">Introduction</a></li>
<li><a href="#getting-setup-1">Getting Setup</a><ul>
<li><a href="#sample-html-with-qunit-compatible-markup">Sample HTML with QUnit-compatible markup:</a></li>
</ul></li>
<li><a href="#assertions">Assertions</a><ul>
<li><a href="#basic-test-case-using-test-name-callback">Basic test case using test( name, callback )</a></li>
<li><a href="#comparing-the-actual-output-of-a-function-against-the-expected-output">Comparing the actual output of a function against the expected output</a></li>
</ul></li>
<li><a href="#adding-structure-to-assertions">Adding structure to assertions</a><ul>
<li><a href="#basic-qunit-modules">Basic QUnit Modules:</a></li>
<li><a href="#using-setup-and-teardown">Using setup() and teardown() :</a></li>
<li><a href="#using-setup-and-teardown-for-instantiation-and-clean-up">Using setup() and teardown() for instantiation and clean-up</a></li>
</ul></li>
<li><a href="#assertion-examples">Assertion examples</a><ul>
<li><a href="#equal---a-comparison-assertion.-it-passes-if-actual-expected">equal - a comparison assertion. It passes if actual == expected</a></li>
<li><a href="#notequal---a-comparison-assertion.-it-passes-if-actual-expected">notEqual - a comparison assertion. It passes if actual != expected</a></li>
<li><a href="#strictequal---a-comparison-assertion.-it-passes-if-actual-expected.">strictEqual - a comparison assertion. It passes if actual === expected.</a></li>
<li><a href="#notstrictequal---a-comparison-assertion.-it-passes-if-actual-expected.">notStrictEqual - a comparison assertion. It passes if actual !== expected.</a></li>
<li><a href="#deepequal---a-recursive-comparison-assertion.-unlike-strictequal-it-works-on-objects-arrays-and-primitives.">deepEqual - a recursive comparison assertion. Unlike strictEqual(), it works on objects, arrays and primitives.</a></li>
<li><a href="#notdeepequal---a-comparison-assertion.-this-returns-the-opposite-of-deepequal">notDeepEqual - a comparison assertion. This returns the opposite of deepEqual</a></li>
<li><a href="#raises---an-assertion-which-tests-if-a-callback-throws-any-exceptions">raises - an assertion which tests if a callback throws any exceptions</a></li>
</ul></li>
<li><a href="#fixtures">Fixtures</a><ul>
<li><a href="#fixture-markup">Fixture markup:</a></li>
<li><a href="#fixtures-example">Fixtures example:</a></li>
</ul></li>
<li><a href="#asynchronous-code">Asynchronous code</a></li>
</ul></li>
<li><a href="#sinonjs">SinonJS</a><ul>
<li><a href="#what-is-sinonjs">What is SinonJS?</a><ul>
<li><a href="#basic-spies">Basic Spies</a></li>
<li><a href="#spying-on-existing-functions">Spying On Existing Functions</a></li>
<li><a href="#inspection-interface">Inspection Interface</a></li>
</ul></li>
<li><a href="#stubs-and-mocks">Stubs and mocks</a><ul>
<li><a href="#stubs">Stubs</a></li>
<li><a href="#mocks">Mocks</a></li>
</ul></li>
<li><a href="#exercise-1">Exercise</a><ul>
<li><a href="#models-3">Models</a></li>
<li><a href="#collections-2">Collections</a></li>
<li><a href="#views-3">Views</a></li>
<li><a href="#app">App</a></li>
</ul></li>
<li><a href="#further-reading-resources">Further Reading & Resources</a></li>
</ul></li>
<li><a href="#resources">Resources</a><ul>
<li><a href="#books-courses">Books & Courses</a></li>
<li><a href="#extensionslibraries">Extensions/Libraries</a></li>
</ul></li>
<li><a href="#conclusions-2">Conclusions</a></li>
<li><a href="#appendix">Appendix</a><ul>
<li><a href="#a-simple-javascript-mvc-implementation">A Simple JavaScript MVC Implementation</a><ul>
<li><a href="#event-system">Event System</a></li>
<li><a href="#models-4">Models</a></li>
<li><a href="#views-4">Views</a></li>
<li><a href="#controllers-2">Controllers</a></li>
<li><a href="#practical-usage">Practical Usage</a></li>
</ul></li>
<li><a href="#mvp">MVP</a><ul>
<li><a href="#models-views-presenters">Models, Views & Presenters</a></li>
</ul></li>
<li><a href="#mvp-or-mvc">MVP or MVC?</a></li>
<li><a href="#mvc-mvp-and-backbone.js">MVC, MVP and Backbone.js</a></li>
<li><a href="#namespacing">Namespacing</a><ul>
<li><a href="#what-is-namespacing">What is namespacing?</a></li>
</ul></li>
<li><a href="#backbone-dependency-details">Backbone Dependency Details</a><ul>
<li><a href="#dom-manipulation">DOM Manipulation</a></li>
<li><a href="#utilities">Utilities</a></li>
<li><a href="#restful-persistence-1">RESTful persistence</a></li>
<li><a href="#routing">Routing</a></li>
</ul></li>
</ul></li>
</ul>
</nav>
<h2 id="prelude"><a href="#TOC">Prelude</a></h2>
<figure>
<img src="img/logo.jpg"><figcaption></figcaption>
</figure>
<p>Not so long ago, <q>data-rich web application</q> was an oxymoron. Today, these applications are everywhere and you need to know how to build them.</p>
<p>Traditionally, web applications left the heavy-lifting of data to servers that pushed HTML to the browser in complete page loads. The use of client-side JavaScript was limited to improving the user experience. Now this relationship has been inverted - client applications pull raw data from the server and render it into the browser when and where it is needed.</p>
<p>Think of the Ajax shopping cart which doesn’t require a refresh on the page when adding an item to your basket. Initially, jQuery became the go-to library for this paradigm. It’s nature was to make Ajax requests then update text on the page and so on. However, this pattern with jQuery revealed that we have implicit model data on the client side. With the server no longer being the only place that knows about our item count, it was a hint that there was a natural tension and pull of this evolution.</p>
<p>The rise of arbitrary code on the client-side which can talk to the server however it sees fit has meant an increase in client-side complexity. Good architecture on the client has gone from an afterthought to essential - you can’t just hack together some jQuery code and expect it to scale as your application grows. Most likely, you would end up with a nightmarish tangle of UI callbacks entwined with business logic, destined to be discarded by the poor soul who inherits your code.</p>
<p>Thankfully, there are a growing number of JavaScript libraries that can help improve the structure and maintainability of your code, making it easier to build ambitious interfaces without a great deal of effort. <a href="http://documentcloud.github.com/backbone/">Backbone.js</a> has quickly become one of the most popular open-source solutions to these issues and in this book we will take you through an in-depth walkthrough of it.</p>
<p>Begin with the fundamentals, work your way through the exercises, and learn how to build an application that is both cleanly organized and maintainable. If you are a developer looking to write code that can be more easily read, structured, and extended - this guide can help.</p>
<p>This book is released under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported <a href="http://creativecommons.org/licenses/by-nc-sa/3.0/">license</a> meaning you can both grab a copy of the book for free or help to further <a href="https://github.com/addyosmani/backbone-fundamentals/">improve</a> it. Corrections to existing material are always welcome and I hope that together we can provide the community with an up-to-date resource that is of help.</p>
<p>My extended thanks go out to <a href="https://github.com/jashkenas">Jeremy Ashkenas</a> and <a href="documentcloud.org">DocumentCloud</a> for creating Backbone.js and <a href="https://github.com/addyosmani/backbone-fundamentals/contributors">these</a> members of the community for their assistance making this project far better than I could have imagined.</p>
<h2 id="target-audience"><a href="#TOC">Target Audience</a></h2>
<p>This book is targeted at novice to intermediate developers wishing to learn how to better structure their client-side code. An understanding of JavaScript fundamentals is required to get the most out of it, however we have tried to provide a basic description of these concepts where possible.</p>
<h2 id="acknowledgements"><a href="#TOC">Acknowledgements</a></h2>
<p>I am indebted to the fantastic work done by the technical reviewers who helped improve this book. Their knowledge, energy, and passion have helped shape it into a better learning resource and they continue to serve as a source of inspiration. Thanks go out to:</p>
<ul>
<li><a href="http://github.com/dcmaf">Marc Friedman</a></li>
<li><a href="https://github.com/derickbailey">Derick Bailey</a></li>
<li><a href="https://github.com/jashkenas">Jeremy Ashkenas</a></li>
<li><a href="https://github.com/samuelclay">Samuel Clay</a></li>
<li><a href="http://github.com/wibblymat">Mat Scales</a></li>
<li><a href="https://github.com/alexgraul">Alex Graul</a></li>
<li><a href="http://github.com/g6scheme">Dusan Gledovic</a></li>
<li><a href="http://github.com/sindresorhus">Sindre Sorhus</a></li>
</ul>
<h2 id="credits"><a href="#TOC">Credits</a></h2>
<p>None of this would have been possible without the time and effort invested by the other developers and authors in the community who contributed to it. I would like to extend my thanks to Derick Bailey, Ryan Eastridge, Jack Franklin, Mike Ball, Uģis Ozols, Björn Ekengren and our other excellent <a href="https://github.com/addyosmani/backbone-fundamentals/graphs/contributors">contributors</a> that made this project possible.</p>
<h2 id="reading"><a href="#TOC">Reading</a></h2>
<p>I assume your level of knowledge about JavaScript goes beyond the basics and as such certain topics such as object literals are skipped. If you need to learn more about the language, I am happy to suggest:</p>
<ul>
<li><a href="http://shop.oreilly.com/product/9780596805531.do">JavaScript: The Definitive Guide</a> by David Flanagan (O’Reilly)</li>
<li><a href="http://www.informit.com/store/effective-javascript-68-specific-ways-to-harness-the-9780321812186">Effective JavaScript</a> by David Herman (Pearson)</li>
<li><a href="http://shop.oreilly.com/product/9780596517748.do">JavaScript: The Good Parts</a> by Douglas Crockford (O’Reilly)</li>
<li><a href="http://www.amazon.com/Object-Oriented-Javascript-Stoyan-Stefanov/dp/1847194141">Object-Oriented JavaScript</a> by Stoyan Stefanov (Packt Publishing)</li>
</ul>
<h1 id="introduction"><a href="#TOC">Introduction</a></h1>
<p>Frank Lloyd Wright once said <q>You can’t make an architect. You can however open the doors and windows toward the light as you see it.</q> In this book, I hope to shed some light on how to improve the structure of your web applications, opening doors to what will hopefully be more maintainable, readable applications in your future.</p>
<p>The goal of all architecture is to build something well; in our case, to craft code that is enduring and delights both ourselves and the developers who will maintain our code long after we are gone. We all want our architecture to be simple, yet beautiful.</p>
<p>Modern JavaScript frameworks and libraries can bring structure and organization to your projects, establishing a maintainable foundation right from the start. They build on the trials and tribulations of developers who have had to work around callback chaos similar to that which you are facing now or may in the near future.</p>
<p>When developing applications using just jQuery, the piece missing is a way to structure and organize your code. It’s very easy to create a JavaScript app that ends up a tangled mess of jQuery selectors and callbacks, all desperately trying to keep data in sync between the HTML for your UI, the logic in your JavaScript, and calls to your API for data.</p>
<p>Without something to help tame the mess, you’re likely to string together a set of independant plugins and libraries to make up the functionality or build everything yourself from scratch and have to maintain it yourself. Backbone solves this problem for you, providing a way to cleanly organize code, separating responsibilities into recognizable pieces that are easy to maintain.</p>
<p>In <q>Developing Backbone.js Applications,</q> I and a number of other experienced authors will show you how to improve your web application structure using the popular JavaScript library, Backbone.js</p>
<h3 id="what-is-mvc"><a href="#TOC">What Is MVC?</a></h3>
<p>A number of modern JavaScript frameworks provide developers an easy path to organizing their code using variations of a pattern known as MVC (Model-View-Controller). MVC separates the concerns in an application into three parts:</p>
<ul>
<li>Models represent the domain-specific knowledge and data in an application. Think of this as being a <q>type</q> of data you can model — like a User, Photo, or Todo note. Models can notify observers when their state changes.</li>
<li>Views typically constitute the user interface in an application (e.g., markup and templates), but don’t have to be. They observe Models, but don’t directly communicate with them.</li>
<li>Controllers handle input (e.g., clicks, user actions) and update Models.</li>
</ul>
<p>Thus, in an MVC application, user input is acted upon by Controllers which update Models. Views observe Models and update the user interface when changes occur.</p>
<p>JavaScript MVC frameworks don’t always strictly follow the above pattern. Some solutions (including Backbone.js) merge the responsibility of the Controller into the View, while other approaches add additional components into the mix.</p>
<p>For this reason we refer to such frameworks as following the MV* pattern; that is, you’re likely to have a Model and a View, but a distinct Controller might not be present and other components may come into play.</p>
<h3 id="what-is-backbone.js"><a href="#TOC">What is Backbone.js?</a></h3>
<figure>
<img src="img/backbonejsorg.jpg"><figcaption></figcaption>
</figure>
<p>Backbone.js is a lightweight JavaScript library that adds structure to your client-side code. It makes it easy to manage and decouple concerns in your application, leaving you with code that is more maintainable in the long term.</p>
<p>Developers commonly use libraries like Backbone.js to create single-page applications (SPAs). SPAs are web applications that load into the browser and then react to data changes on the client side without requiring complete page refreshes from the server.</p>
<p>Backbone is mature, popular, and has both a vibrant developer community as well as a wealth of plugins and extensions available that build upon it. It has been used to create non-trivial applications by companies such as Disqus, Walmart, SoundCloud and LinkedIn.</p>
<p>Backbone focuses on giving you helpful methods for querying and manipulating your data rather than re-inventing the JavaScript object model. It’s a library, rather than a framework, that plays well with others and scales well, from embedded widgets to large-scale applications.</p>
<p>As it’s small, there is also less your users have to download on mobile or slower connections. The entire Backbone source can be read and understood in just a few hours.</p>
<h3 id="when-do-i-need-a-javascript-mvc-framework"><a href="#TOC">When Do I Need A JavaScript MVC Framework?</a></h3>
<p>When building a single-page application using JavaScript, whether it involves a complex user interface or is simply trying to reduce the number of HTTP requests required for new Views, you will likely find yourself inventing many of the pieces that make up an MV* framework.</p>
<p>At the outset, it isn’t terribly difficult to write your own application framework that offers some opinionated way to avoid spaghetti code; however, to say that it is equally as trivial to write something as robust as Backbone would be a grossly incorrect assumption.</p>
<p>There’s a lot more that goes into structuring an application than tying together a DOM manipulation library, templating, and routing. Mature MV* frameworks typically include not only the pieces you would find yourself writing, but also include solutions to problems you’ll find yourself running into later on down the road. This is a time-saver that you shouldn’t underestimate the value of.</p>
<p>So, where will you likely need an MV* framework and where won’t you?</p>
<p>If you’re writing an application where much of the heavy lifting for view rendering and data manipulation will be occurring in the browser, you may find a JavaScript MV* framework useful. Examples of applications that fall into this category are GMail, NewsBlur and the LinkedIn mobile app.</p>
<p>These types of applications typically download a single payload containing all the scripts, stylesheets, and markup users need for common tasks and then perform a lot of additional behavior in the background. For instance, it’s trivial to switch between reading an email or document to writing one without sending a new page request to the server.</p>
<p>If, however, you’re building an application that still relies on the server for most of the heavy-lifting of page/view rendering and you’re just using a little JavaScript or jQuery to make things more interactive, an MV* framework may be overkill. There certainly are complex Web applications where the partial rendering of views can be coupled with a single-page application effectively, but for everything else, you may find yourself better sticking to a simpler setup.</p>
<p>Maturity in software (framework) development isn’t simply about how long a framework has been around. It’s about how solid the framework is and more importantly how well it’s evolved to fill its role. Has it become more effective at solving common problems? Does it continue to improve as developers build larger and more complex applications with it?</p>
<h3 id="why-consider-backbone.js"><a href="#TOC">Why Consider Backbone.js?</a></h3>
<p>Backbone provides a minimal set of data-structuring (Models, Collections) and user interface (Views, URLs) primitives that are helpful when building dynamic applications using JavaScript. It’s not opinionated, meaning you have the freedom and flexibility to build the best experience for your web application how you see fit. You can either use the prescribed architecture it offers out of the box or extend it to meet your requirements.</p>
<p>The library doesn’t focus on widgets or replacing the way you structure objects - it just supplies you with utilities for manipulating and querying data in your application. It also doesn’t prescribe a specific template engine - while you are free to use the Micro-templating offered by Underscore.js (one of it’s dependencies), views can bind to HTML constructed using your templating solution of choice.</p>
<p>Looking at the <a href="http://backbonejs.org/#examples">large</a> number of applications built with Backbone, it’s clear that it scales well. Backbone also works quite well with other libraries, meaning you can embed Backbone widgets in an application written with AngularJS, use it with TypeScript, or just use an individual class (like Models) as a data backer for simpler apps.</p>
<p>There are no performance drawbacks to using Backbone to structure your application. It avoids run loops, two-way binding, and constant polling of your data structures for updates and tries to keep things simple where possible. That said, should you wish to go against the grain, you can of course implement such things on top of it. Backbone won’t stop you.</p>
<p>With a vibrant community of plugin and extension authors, there’s a liklihood that if you’re looking to achieve some behavior Backbone is lacking, a complementary project exists that works well with it. This is made simpler by Backbone offering literate documentation of it’s source code, allowing anyone an opportunity to easily understand what is going on behind the scenes.</p>
<p>Having been refined over two and a half years of development, Backbone is a mature library that will continue to offer a minimalist solution for building better web applications. I regularly use it and hope that you find it as useful an addition to your toolbelt as I have.</p>
<h3 id="setting-expectations"><a href="#TOC">Setting Expectations</a></h3>
<p>The goal of this book is to create an authoritative and centralized repository of information that can help those developing real-world apps with Backbone. If you come across a section or topic which you think could be improved or expanded on, please feel free to submit an issue (or better yet, a pull-request) on the book’s <a href="https://github.com/addyosmani/backbone-fundamentals">GitHub site</a>. It won’t take long and you’ll be helping other developers avoid the problems you ran into.</p>
<p>Topics will include MVC theory and how to build applications using Backbone’s Models, Views, Collections, and Routers. I’ll also be taking you through advanced topics like modular development with Backbone.js and AMD (via RequireJS), solutions to common problems like nested views, how to solve routing problems with Backbone and jQuery Mobile, and much more.</p>
<p>Here is a peek at what you will be learning in each chapter:</p>
<p><i>Chapter 2, Fundamentals</i> traces the history of the MVC design pattern and introduces how it is implemented by Backbone.js and other JavaScript frameworks.</p>
<p><i>Chapter 3, Backbone Basics</i> covers the major features of the core Backbone.js framework and technologies and techniques you will need to know in order to apply it.</p>
<p><i>Chapter 4, Exercise 1: Todos - Your First Backbone.js App</i> takes you step-by-step through development of a simple client-side Todo List application.</p>
<p><i>Chapter 5, Exercise 2: Book Library - Your First RESTful Backbone.js App</i> walks you through development of a Book Library application which persists its model to a server using a REST API.</p>
<p><i>Chapter 6, Backbone Extensions</i> describes Backbone.Marionette and Thorax, two extension frameworks which add features to Backbone.js that are useful for developing large-scale applications.</p>
<p><i>Chapter 7, Common Problems and Solutions</i> reviews common issues you may encounter when using Backbone.js and ways of addressing them.</p>
<p><i>Chapter 8, Modular Development</i> looks at how AMD modules and RequireJS can be used to modularize your code.</p>
<p><i>Chapter 9, Backbone Boilerplate And Grunt BBB</i> introduces powerful tools you can use to bootstrap a new Backbone.js application with boilerplate code.</p>
<p><i>Chapter 10, Mobile Applications</i> addresses the issues that arise when using Backbone with jQuery Mobile.</p>
<p><i>Chapter 11, Jasmine</i> covers how to unit test Backbone code using the Jasmine test framework.</p>
<p><i>Chapter 12, QUnit</i> discusses how to use the QUnit for unit testing.</p>
<p><i>Chapter 13, SinonJS</i> discusses how to use SinonJS for unit testing your Backbone apps.</p>
<p><i>Chapter 14, Resources</i> provides references to additional Backbone-related resources.</p>
<p><i>Chapter 15, Conclusions</i> wraps up the our tour through the world of Backbone.js development.</p>
<p><i>Chapter 16, Appendix</i> returns to our design pattern discussion by contrasting MVC with the Model-View-Presenter (MVP) pattern and examines how Backbone.js relates to the two patterns. It also provides useful information for existing Backbone users who may be upgrading from Backbone 0.9.2 to version 0.9.10 and beyond.</p>
<h1 id="fundamentals"><a href="#TOC">Fundamentals</a></h1>
<p>Design patterns are proven solutions to common development problems that can help us improve the organization and structure of our applications. By using patterns, we benefit from the collective experience of skilled developers who have repeatedly solved similar problems.</p>
<p>Historically, developers creating desktop and server-class applications have had a wealth of design patterns available for them to lean on, but it’s only been in the past few years that such patterns have been applied to client-side development.</p>
<p>In this chapter, we’re going to explore the evolution of the Model-View-Controller (MVC) design pattern and get our first look at how the Backbone.js framework allows us to apply this pattern to client-side development.</p>
<h2 id="mvc"><a href="#TOC">MVC</a></h2>
<p>MVC is an architectural design pattern that encourages improved application organization through a separation of concerns. It enforces the isolation of business data (Models) from user interfaces (Views), with a third component (Controllers) traditionally managing logic, user-input, and coordination of Models and Views. The pattern was originally designed by <a href="http://en.wikipedia.org/wiki/Trygve_Reenskaug">Trygve Reenskaug</a> while working on Smalltalk-80 (1979), where it was initially called Model-View-Controller-Editor. MVC was described in depth in <a href="http://www.amazon.co.uk/Design-patterns-elements-reusable-object-oriented/dp/0201633612"><q>Design Patterns: Elements of Reusable Object-Oriented Software</q></a> (The <q>GoF</q> or <q>Gang of Four</q> book) in 1994, which played a role in popularizing its use.</p>
<h3 id="smalltalk-80-mvc"><a href="#TOC">Smalltalk-80 MVC</a></h3>
<p>It’s important to understand the issues that the original MVC pattern was aiming to solve as it has changed quite heavily since the days of its origin. Back in the 70’s, graphical user-interfaces were few and far between. An approach known as <a href="http://martinfowler.com/eaaDev/uiArchs.html">Separated Presentation</a> began to be used as a means to make a clear division between domain objects which modeled concepts in the real world (e.g., a photo, a person) and the presentation objects which were rendered to the user’s screen.</p>
<p>The Smalltalk-80 implementation of MVC took this concept further and had an objective of separating out the application logic from the user interface. The idea was that decoupling these parts of the application would also allow the reuse of Models for other interfaces in the application. There are some interesting points worth noting about Smalltalk-80’s MVC architecture:</p>
<ul>
<li>A Domain element was known as a Model and was ignorant of the user-interface (Views and Controllers)</li>
<li>Presentation was taken care of by the View and the Controller, but there wasn’t just a single View and Controller. A View-Controller pair was required for each element being displayed on the screen and so there was no true separation between them</li>
<li>The Controller’s role in this pair was handling user input (such as key-presses and click events) and doing something sensible with them</li>
<li>The Observer pattern was used to update the View whenever the Model changed</li>
</ul>
<p>Developers are sometimes surprised when they learn that the Observer pattern (nowadays commonly implemented as a Publish/Subscribe system) was included as a part of MVC’s architecture decades ago. In Smalltalk-80’s MVC, the View and Controller both observe the Model: anytime the Model changes, the Views react. A simple example of this is an application backed by stock market data - for the application to show real-time information, any change to the data in its Model should result in the View being refreshed instantly.</p>
<p>Martin Fowler has done an excellent job of writing about the <a href="http://martinfowler.com/eaaDev/uiArchs.html">origins</a> of MVC over the years and if you are interested in further historical information about Smalltalk-80’s MVC, I recommend reading his work.</p>
<h3 id="mvc-applied-to-the-web"><a href="#TOC">MVC Applied To The Web</a></h3>
<p>The web heavily relies on the HTTP protocol, which is stateless. This means that there is not a constantly open connection between the browser and server; each request instantiates a new communication channel between the two. Once the request initiator (e.g. a browser) gets a response the connection is closed. This fact creates a completely different context when compared to the one of the operating systems on which many of the original MVC ideas were developed. The MVC implementation has to conform to the web context.</p>
<p>An example of a server-side web application framework which tries to apply MVC to the web context is <a href="http://guides.rubyonrails.org/">Ruby On Rails</a>.</p>
<figure>
<img src="img/rails_mvc.png"><figcaption></figcaption>
</figure>
<p>At it’s core are the three MVC components we would expect - the Model, View and Controller architecture. In Rails:</p>
<ul>
<li>Models represent the data in an application and are typically used to manage rules for interacting with a specific database table. You generally have one table corresponding to one model with much of your application’s business logic living within these models.</li>
<li>Views represent your user interface, often taking the form of HTML that will be sent down to the browser. They’re used to present application data to anything making requests from your application.</li>
<li>Controllers offer the glue between models and views. Their responsibility is to process requests from the browser, ask your models for data and then supply this data to views so that they may be presented to the browser.</li>
</ul>
<p>Although there’s a clear separation of concerns that is MVC-like in Rails, it is actually using a different pattern called <a href="http://en.wikipedia.org/wiki/Model2">Model2</a>. Justifications for this include that Rails does not notify views from the model and controllers just pass model data directly to the view.</p>
<p>That said, even for the server-side workflow of receiving a request from a URL, baking out an HTML page as a response and separating your business logic from your interface has many benefits. In the same way that keeping your UI cleanly separate from your database records is useful in server-side frameworks, it’s equally as useful to keep your UI cleanly separated from your data models in JavaScript (as we will read more about shortly).</p>
<p>Other server-side implementations of MVC (such as the PHP <a href="http://zend.com">Zend</a> framework) also implement the <a href="http://en.wikipedia.org/wiki/Front_Controller_pattern">Front Controller</a> design pattern. This pattern layers an MVC stack behind a single point of entry. This single point of entry means that all HTTP requests (e.g., <code>http://www.example.com</code>, <code>http://www.example.com/whichever-page/</code>, etc.) are routed by the server’s configuration to the same handler, independent of the URI.</p>
<p>When the Front Controller receives an HTTP request it analyzes it and decides which class (Controller) and method (Action) to invoke. The selected Controller Action takes over and interacts with the appropriate Model to fulfill the request. The Controller receives data back from the Model, loads an appropriate View, injects the Model data into it, and returns the response to the browser.</p>
<p>For example, let’s say we have our blog on <code>www.example.com</code> and we want to edit an article (with <code>id=43</code>) and request <code>http://www.example.com/article/edit/43</code>:</p>
<p>On the server side, the Front Controller would analyze the URL and invoke the Article Controller (corresponding to the <code>/article/</code> part of the URI) and its Edit Action (corresponding to the <code>/edit/</code> part of the URI). Within the Action there would be a call to, let’s say, the Articles Model and its <code>Articles::getEntry(43)</code> method (43 corresponding to the <code>/43</code> at the end of the URI). This would return the blog article data from the database for edit. The Article Controller would then load the (<code>article/edit</code>) View which would include logic for injecting the article’s data into a form suitable for editing its content, title, and other (meta) data. Finally, the resulting HTML response would be returned to the browser.</p>
<p>As you can imagine, a similar flow is necessary with POST requests after we press a save button in a form. The POST action URI would look like <code>/article/save/43</code>. The request would go through the same Controller, but this time the Save Action would be invoked (due to the <code>/save/</code> URI chunk), the Articles Model would save the edited article to the database with <code>Articles::saveEntry(43)</code>, and the browser would be redirected to the <code>/article/edit/43</code> URI for further editing.</p>
<p>Finally, if the user requested <code>http://www.example.com/</code> the Front Controller would invoke the default Controller and Action; e.g., the Index Controller and its Index action. Within Index Action there would be a call to the Articles model and its <code>Articles::getLastEntries(10)</code> method which would return the last 10 blog posts. The Controller would load the blog/index View which would have basic logic for listing the blog posts.</p>
<p>The picture below shows this typical HTTP request/response lifecycle for server-side MVC:</p>
<figure>
<img src="img/webmvcflow_bacic.png"><figcaption></figcaption>
</figure>
<p>The Server receives an HTTP request and routes it through a single entry point. At that entry point, the Front Controller analyzes the request and based on it invokes an Action of the appropriate Controller. This process is called routing. The Action Model is asked to return and/or save submitted data. The Model communicates with the data source (e.g., database or API). Once the Model completes its work it returns data to the Controller which then loads the appropriate View. The View executes presentation logic (loops through articles and prints titles, content, etc.) using the supplied data. In the end, an HTTP response is returned to the browser.</p>
<h3 id="client-side-mvc-single-page-apps"><a href="#TOC">Client-Side MVC & Single Page Apps</a></h3>
<p>Several <a href="http://radar.oreilly.com/2009/07/velocity-making-your-site-fast.html">studies</a> have confirmed that improvements to latency can have a positive impact on the usage and user engagement of sites and apps. This is at odds with the traditional approach to web app development which is very server-centric, requiring a complete page reload to move from one page to the next. Even with heavy caching in place, the browser still has to parse the CSS, JavaScript, and HTML and render the interface to the screen.</p>
<p>In addition to resulting in a great deal of duplicated content being served back to the user, this approach affects both latency and the general responsiveness of the user experience. A trend to improve perceived latency in the past few years has been to move towards building Single Page Applications (SPAs) - apps which after an initial page load are able to handle subsequent navigations and requests for data without the need for a complete reload.</p>
<p>When a user navigates to a new view, additional content required for the view is requested using an XHR (XMLHttpRequest), typically communicating with a server-side REST API or endpoint. <a href="https://en.wikipedia.org/wiki/Ajax_(programming)">Ajax</a>(Asynchronous JavaScript and XML) makes communication with the server asynchronous so that data is transferred and processed in the background, allowing the user to work on other parts of a page without interaction. This improves usability and responsiveness.</p>
<p>SPAs can also take advantage of browser features like the <a href="http://diveintohtml5.info/history.html">History API</a> to update the address seen in the location bar when moving from one view to another. These URLs also make it possible to bookmark and share a particular application state, without the need to navigate to completely new pages.</p>
<p>The typical SPA consists of smaller pieces of interface representing logical entities, all of which have their own UI, business logic and data. A good example is a basket in a shopping web application which can have items added to it. This basket might be presented to the user in a box in the top right corner of the page (see the picture below):</p>
<figure>
<img src="img/wireframe_e_commerce.png"><figcaption></figcaption>
</figure>
<p>The basket and its data are presented in HTML. The data and its associated View in HTML changes over time. There was a time when we used jQuery (or a similar DOM manipulation library) and a bunch of Ajax calls and callbacks to keep the two in sync. That often produced code that was not well-structured or easy to maintain. Bugs were frequent and perhaps even unavoidable.</p>
<p>The need for fast, complex, and responsive Ajax-powered web applications demands replication of a lot of this logic on the client side, dramatically increasing the size and complexity of the code residing there. Eventually this has brought us to the point where we need MVC (or a similar architecture) implemented on the client side to better structure the code and make it easier to maintain and further extend during the application life-cycle.</p>
<p>Through evolution and trial and error, JavaScript developers have harnessed the power of the traditional MVC pattern, leading to the development of several MVC-inspired JavaScript frameworks, such as Backbone.js.</p>
<h3 id="client-side-mvc---backbone-style"><a href="#TOC">Client-Side MVC - Backbone Style</a></h3>
<p>Let’s take our first look at how Backbone.js brings the benefits of MVC to client-side development using a Todo application as our example. We will build on this example in the coming chapters when we explore Backbone’s features but for now we will just focus on the core components’ relationships to MVC.</p>
<p>Our example will need a div element to which we can attach a list of Todo’s. It will also need an HTML template containing a placeholder for a Todo item title and a completion checkbox which can be instantiated for Todo item instances. These are provided by the following HTML:</p>
<pre class="sourceCode html"><code class="sourceCode html"><span class="er"><</span>!doctype html>
<span class="kw"><html</span><span class="ot"> lang=</span><span class="st">"en"</span><span class="kw">></span>
<span class="kw"><head></span>
<span class="kw"><meta</span><span class="ot"> charset=</span><span class="st">"utf-8"</span><span class="kw">></span>
<span class="kw"><title></title></span>
<span class="kw"><meta</span><span class="ot"> name=</span><span class="st">"description"</span><span class="ot"> content=</span><span class="st">""</span><span class="kw">></span>
<span class="kw"></head></span>
<span class="kw"><body></span>
<span class="kw"><div</span><span class="ot"> id=</span><span class="st">"todo"</span><span class="kw">></span>
<span class="kw"></div></span>
<span class="kw"><script</span><span class="ot"> type=</span><span class="st">"text/template"</span><span class="ot"> id=</span><span class="st">"item-template"</span><span class="kw">></span>
<div>
<input id=<span class="st">"todo</span>_<span class="st">complete"</span> type=<span class="st">"checkbox"</span> <%= completed ? <span class="ch">'checked</span>="<span class="ch">checked</span>"<span class="ch">'</span> : <span class="ch">''</span> %>>
<%- title %>
</div>
<span class="kw"></script></span>
<span class="kw"><script</span><span class="ot"> src=</span><span class="st">"jquery.js"</span><span class="kw">></script></span>
<span class="kw"><script</span><span class="ot"> src=</span><span class="st">"underscore.js"</span><span class="kw">></script></span>
<span class="kw"><script</span><span class="ot"> src=</span><span class="st">"backbone.js"</span><span class="kw">></script></span>
<span class="kw"><script</span><span class="ot"> src=</span><span class="st">"demo.js"</span><span class="kw">></script></span>
<span class="kw"></body></span>
<span class="kw"></html></span></code></pre>
<p>In our Todo application (demo.js), Backbone Model instances are used to hold the data for each Todo item:</p>
<pre class="sourceCode javascript"><code class="sourceCode javascript"><span class="co">// Define a Todo Model</span>
<span class="kw">var</span> Todo = <span class="kw">Backbone.Model</span>.<span class="fu">extend</span>({
<span class="co">// Default todo attribute values</span>
<span class="dt">defaults</span>: {
<span class="dt">title</span>: <span class="ch">''</span>,
<span class="dt">completed</span>: <span class="kw">false</span>
}
});
<span class="co">// Instantiate the Todo Model with a title, allowing completed attribute</span>
<span class="co">// to default to false</span>
<span class="kw">var</span> myTodo = <span class="kw">new</span> Todo({
<span class="dt">title</span>: <span class="ch">'Check attributes property of the logged models in the console.'</span>
});</code></pre>
<p>Our Todo Model extends Backbone.Model and simply defines default values for two data attributes. As you will discover in the upcoming chapters, Backbone Models provide many more features but this simple Model illustrates that first and foremost a Model is a data container.</p>
<p>Each Todo instance will be rendered on the page by a TodoView:</p>
<pre class="sourceCode javascript"><code class="sourceCode javascript"><span class="kw">var</span> TodoView = <span class="kw">Backbone.View</span>.<span class="fu">extend</span>({
<span class="dt">tagName</span>: <span class="ch">'li'</span>,
<span class="co">// Cache the template function for a single item.</span>
<span class="dt">todoTpl</span>: <span class="kw">_</span>.<span class="fu">template</span>( $(<span class="ch">'#item-template'</span>).<span class="fu">html</span>() ),
<span class="dt">events</span>: {
<span class="ch">'dblclick label'</span>: <span class="ch">'edit'</span>,
<span class="ch">'keypress .edit'</span>: <span class="ch">'updateOnEnter'</span>,
<span class="ch">'blur .edit'</span>: <span class="ch">'close'</span>
},
<span class="co">// Called when the view is first created</span>
<span class="dt">initialize</span>: <span class="kw">function</span> () {
<span class="kw">this</span>.$<span class="fu">el</span> = $(<span class="ch">'#todo'</span>);
<span class="co">// Later we'll look at:</span>
<span class="co">// this.listenTo(someCollection, 'all', this.render);</span>
<span class="co">// but you can actually run this example right now by</span>
<span class="co">// calling TodoView.render();</span>
},
<span class="co">// Re-render the titles of the todo item.</span>
<span class="dt">render</span>: <span class="kw">function</span>() {
<span class="kw">this</span>.$<span class="fu">el</span>.<span class="fu">html</span>( <span class="kw">this</span>.<span class="fu">todoTpl</span>( <span class="kw">this</span>.<span class="fu">model</span>.<span class="fu">toJSON</span>() ) );
<span class="kw">this</span>.<span class="fu">input</span> = <span class="kw">this</span>.$(<span class="ch">'.edit'</span>);
<span class="kw">return</span> <span class="kw">this</span>;
},
<span class="dt">edit</span>: <span class="kw">function</span>() {
<span class="co">// executed when todo label is double clicked</span>
},
<span class="dt">close</span>: <span class="kw">function</span>() {
<span class="co">// executed when todo loses focus</span>
},
<span class="dt">updateOnEnter</span>: <span class="kw">function</span>( e ) {
<span class="co">// executed on each keypress when in todo edit mode, </span>
<span class="co">// but we'll wait for enter to get in action</span>
}
});
<span class="co">// create a view for a todo</span>
<span class="kw">var</span> todoView = <span class="kw">new</span> TodoView({<span class="dt">model</span>: myTodo});</code></pre>
<p>TodoView is defined by extending Backbone.View and is instantiated with an associated Model. In our example, the <code>render()</code> method uses a template to construct the HTML for the Todo item which is placed inside a li element. Each call to <code>render()</code> will replace the content of the li element using the current Model data. Thus, a View instance renders the content of a DOM element using the attributes of an associated Model. Later we will see how a View can bind its <code>render()</code> method to Model change events, causing the View to re-render whenever the Model changes.</p>
<p>So far, we have seen that Backbone.Model implements the Model aspect of MVC and Backbone.View implements the View. However, as we noted earlier, Backbone departs from traditional MVC when it comes to Controllers - there is no Backbone.Controller!</p>
<p>Instead, the Controller responsibility is addressed within the View. Recall that Controllers respond to requests and perform appropriate actions which may result in changes to the Model and updates to the View. In a single-page application, rather than having requests in the traditional sense, we have events. Events can be traditional browser DOM events (e.g., clicks) or internal application events such as Model changes.</p>
<p>In our TodoView, the <code>events</code> attribute fulfills the role of the Controller configuration, defining how events occurring within the View’s DOM element are to be routed to event-handling methods defined in the View.</p>
<p>While in this instance events help us relate Backbone to the MVC pattern, we will see them playing a much larger role in our SPA applications. Backbone.Event is a fundamental Backbone component which is mixed into both Backbone.Model and Backbone.View, providing them with rich event management capabilities. Note that the traditional controller role (Smalltalk-80 style) is performed by the template, not by the Backbone.View.</p>
<p>This completes our first encounter with Backbone.js. The remainder of this book will explore the many features of the framework which build on these simple constructs. Before moving on, let’s take a look at common features of JavaScript MV* frameworks.</p>
<h3 id="implementation-specifics"><a href="#TOC">Implementation Specifics</a></h3>
<p>The picture below shows the typical HTTP request/response lifecycle for client-side MVC using Backbone:</p>
<figure>
<img src="img/backbone_mvc.png"><figcaption></figcaption>
</figure>
<h4 id="models"><a href="#TOC">Models</a></h4>
<ul>
<li><p>The built-in capabilities of Models vary across frameworks; however, it’s common for them to support validation of attributes, where attributes represent the properties of the Model, such as a Model identifier.</p></li>
<li><p>When using Models in real-world applications we generally also need a way of persisting Models. Persistence allows us to edit and update Models with the knowledge that their most recent states will be saved somewhere, for example in a web browser’s localStorage data-store or synchronized with a database.</p></li>
<li><p>A Model may have multiple Views observing it for changes. By <em>observing</em> we mean that a View has registered an interest in being informed whenever an update is made to the Model. This allows the View to ensure that what is displayed on screen is kept in sync with the data contained in the model. Depending on your requirements, you might create a single View displaying all Model attributes, or create separate Views displaying different attributes. The important point is that the Model doesn’t care how these Views are organized, it simply announces updates to its data as necessary through the framework’s event system.</p></li>
<li><p>It is not uncommon for modern MVC/MV* frameworks to provide a means of grouping Models together. In Backbone, these groups are called Collections. Managing Models in groups allows us to write application logic based on notifications from the group when a Model within the group changes. This avoids the need to manually observe individual Model instances. We’ll see this in action later in the book. Collections are also useful for performing any aggregate computations across more than one model.</p></li>
</ul>
<h4 id="views"><a href="#TOC">Views</a></h4>
<ul>
<li><p>Users interact with Views, which usually means reading and editing Model data. For example, in our Todo application, Todo Model viewing happens in the user interface in the list of all Todo items. Within it, each Todo is rendered with its title and completed checkbox. Model editing is done through an <q>edit</q> View where a user who has selected a specific Todo edits its title in a form.</p></li>
<li><p>We define a <code>render()</code> utility within our View which is responsible for rendering the contents of the <code>Model</code> using a JavaScript templating engine (provided by Underscore.js) and updating the contents of our View, referenced by <code>this.el</code>.</p></li>
<li><p>We then add our <code>render()</code> callback as a Model subscriber, so the View can be triggered to update when the Model changes.</p></li>
<li><p>You may wonder where user interaction comes into play here. When users click on a Todo element within the View, it’s not the View’s responsibility to know what to do next. A Controller makes this decision. In Backbone, this is achieved by adding an event listener to the Todo’s element which delegates handling of the click to an event handler.</p></li>
</ul>
<p><strong>Templating</strong></p>
<p>In the context of JavaScript frameworks that support MVC/MV*, it is worth looking more closely at JavaScript templating and its relationship to Views.</p>
<p>It has long been considered bad practice (and computationally expensive) to manually create large blocks of HTML markup in-memory through string concatenation. Developers using this technique often find themselves iterating through their data, wrapping it in nested divs and using outdated techniques such as <code>document.write</code> to inject the <q>template</q> into the DOM. This approach often means keeping scripted markup inline with standard markup, which can quickly become difficult to read and maintain, especially when building large applications.</p>
<p>JavaScript templating libraries (such as Mustache or Handlebars.js) are often used to define templates for Views as HTML markup containing template variables. These template blocks can be either stored externally or within script tags with a custom type (e.g <q>text/template</q>). Variables are delimited using a variable syntax (e.g <code><%= title %></code> for Underscore and <code>{{title}}</code> for Handlebars).</p>
<p>JavaScript template libraries typically accept data in a number of formats, including JSON; a serialisation format that is always a string. The grunt work of populating templates with data is generally taken care of by the framework itself. This has several benefits, particularly when opting to store templates externally which enables applications to load templates dynamically on an as-needed basis.</p>
<p>Let’s compare two examples of HTML templates. One is implemented using the popular Handlebars.js library, and the other uses Underscore’s <q>microtemplates</q>.</p>
<p><strong>Handlebars.js:</strong></p>
<pre class="sourceCode html"><code class="sourceCode html"><span class="kw"><div</span><span class="ot"> class=</span><span class="st">"view"</span><span class="kw">></span>
<span class="kw"><input</span><span class="ot"> class=</span><span class="st">"toggle"</span><span class="ot"> type=</span><span class="st">"checkbox"</span> <span class="er">{{#if</span><span class="ot"> completed</span><span class="er">}}</span> <span class="er">"checked"</span> <span class="er">{{/if}}</span><span class="kw">></span>
<span class="kw"><label></span>{{title}}<span class="kw"></label></span>
<span class="kw"><button</span><span class="ot"> class=</span><span class="st">"destroy"</span><span class="kw">></button></span>
<span class="kw"></div></span>
<span class="kw"><input</span><span class="ot"> class=</span><span class="st">"edit"</span><span class="ot"> value=</span><span class="st">"{{title}}"</span><span class="kw">></span></code></pre>
<p><strong>Underscore.js Microtemplates:</strong></p>
<pre class="sourceCode html"><code class="sourceCode html"><span class="kw"><div</span><span class="ot"> class=</span><span class="st">"view"</span><span class="kw">></span>
<span class="kw"><input</span><span class="ot"> class=</span><span class="st">"toggle"</span><span class="ot"> type=</span><span class="st">"checkbox"</span> <span class="er"><%</span><span class="ot">=</span> <span class="st">completed</span> <span class="st">?</span> <span class="er">'checked'</span><span class="ot"> :</span> <span class="er">''</span> <span class="er">%</span><span class="kw">></span>>
<span class="kw"><label></span><span class="er"><</span>%- title %><span class="kw"></label></span>
<span class="kw"><button</span><span class="ot"> class=</span><span class="st">"destroy"</span><span class="kw">></button></span>
<span class="kw"></div></span>
<span class="kw"><input</span><span class="ot"> class=</span><span class="st">"edit"</span><span class="ot"> value=</span><span class="st">"</span><span class="er"><</span><span class="st">%= title %>"</span><span class="kw">></span></code></pre>
<p>You may also use double curly brackets (i.e <code>{{}}</code>) (or any other tag you feel comfortable with) in Microtemplates. In the case of curly brackets, this can be done by setting the Underscore <code>templateSettings</code> attribute as follows:</p>
<pre class="sourceCode javascript"><code class="sourceCode javascript"><span class="kw">_</span>.<span class="fu">templateSettings</span> = { <span class="dt">interpolate </span>: <span class="ot">/</span><span class="fl">\{\{(</span><span class="ot">.</span><span class="fl">+?)\}\}</span><span class="ot">/g</span> };</code></pre>
<p><strong>A note on Navigation and State</strong></p>
<p>It is also worth noting that in classical web development, navigating between independent views required the use of a page refresh. In single-page JavaScript applications, however, once data is fetched from a server via Ajax, it can be dynamically rendered in a new view within the same page. Since this doesn’t automatically update the URL, the role of navigation thus falls to a <q>router</q>, which assists in managing application state (e.g., allowing users to bookmark a particular view they have navigated to). As routers are neither a part of MVC nor present in every MVC-like framework, I will not be going into them in greater detail in this section.</p>
<h4 id="controllers"><a href="#TOC">Controllers</a></h4>
<p>In our Todo application, a Controller would be responsible for handling changes the user made in the edit View for a particular Todo, updating a specific Todo Model when a user has finished editing.</p>
<p>It’s with Controllers that most JavaScript MVC frameworks depart from the traditional interpretation of the MVC pattern. The reasons for this vary, but in my opinion, Javascript framework authors likely initially looked at server-side interpretations of MVC (such as Ruby on Rails), realized that the approach didn’t translate 1:1 on the client-side, and so re-interpreted the C in MVC to solve their state management problem. This was a clever approach, but it can make it hard for developers coming to MVC for the first time to understand both the classical MVC pattern and the <q>proper</q> role of Controllers in other JavaScript frameworks.</p>
<p>So does Backbone.js have Controllers? Not really. Backbone’s Views typically contain <q>Controller</q> logic, and Routers are used to help manage application state, but neither are true Controllers according to classical MVC.</p>
<p>In this respect, contrary to what might be mentioned in the official documentation or in blog posts, Backbone isn’t truly an MVC framework. It’s in fact better to see it a member of the MV* family which approaches architecture in its own way. There is of course nothing wrong with this, but it is important to distinguish between classical MVC and MV* should you be relying on discussions of MVC to help with your Backbone projects.</p>
<h2 id="what-does-mvc-give-us"><a href="#TOC">What does MVC give us?</a></h2>
<p>To summarize, the MVC pattern helps you keep your application logic separate from your user interface, making it easier to change and maintain both. Thanks to this separation of logic, it is more clear where changes to your data, interface, or business logic need to be made and for what your unit tests should be written.</p>
<h3 id="delving-deeper-into-mvc"><a href="#TOC">Delving Deeper into MVC</a></h3>
<p>Right now, you likely have a basic understanding of what the MVC pattern provides, but for the curious, we’ll explore it a little further.</p>
<p>The GoF (Gang of Four) do not refer to MVC as a design pattern, but rather consider it a <q>set of classes to build a user interface.</q> In their view, it’s actually a variation of three other classical design patterns: the Observer (Publish/Subscribe), Strategy, and Composite patterns. Depending on how MVC has been implemented in a framework, it may also use the Factory and Decorator patterns. I’ve covered some of these patterns in my other free book, <q>JavaScript Design Patterns For Beginners</q> if you would like to read about them further.</p>
<p>As we’ve discussed, Models represent application data, while Views handle what the user is presented on screen. As such, MVC relies on Publish/Subscribe for some of its core communication (something that surprisingly isn’t covered in many articles about the MVC pattern). When a Model is changed it <q>publishes</q> to the rest of the application that it has been updated. The <q>subscriber,</q> generally a Controller, then updates the View accordingly. The observer-viewer nature of this relationship is what facilitates multiple Views being attached to the same Model.</p>
<p>For developers interested in knowing more about the decoupled nature of MVC (once again, depending on the implementation), one of the goals of the pattern is to help define one-to-many relationships between a topic and its observers. When a topic changes, its observers are updated. Views and Controllers have a slightly different relationship. Controllers facilitate Views’ responses to different user input and are an example of the Strategy pattern.</p>
<h3 id="summary"><a href="#TOC">Summary</a></h3>
<p>Having reviewed the classical MVC pattern, you should now understand how it allows developers to cleanly separate concerns in an application. You should also now appreciate how JavaScript MVC frameworks may differ in their interpretation of MVC, and how they share some of the fundamental concepts of the original pattern.</p>
<p>When reviewing a new JavaScript MVC/MV* framework, remember - it can be useful to step back and consider how it’s opted to approach Models, Views, Controllers or other alternatives, as this can better help you understand how the framework is intended to be used.</p>
<h3 id="further-reading"><a href="#TOC">Further reading</a></h3>
<p>If you are interested in learning more about the variation of MVC which Backbone.js uses, please see the MVP (Model-View-Presenter) section in the appendix.</p>
<h2 id="fast-facts"><a href="#TOC">Fast facts</a></h2>
<h3 id="backbone.js"><a href="#TOC">Backbone.js</a></h3>
<ul>
<li>Core components: Model, View, Collection, Router. Enforces its own flavor of MV*</li>
<li>Event-driven communication between Views and Models. As we’ll see, it’s relatively straight-forward to add event listeners to any attribute in a Model, giving developers fine-grained control over what changes in the View</li>
<li>Supports data bindings through manual events or a separate Key-value observing (KVO) library</li>
<li>Support for RESTful interfaces out of the box, so Models can be easily tied to a backend</li>
<li>Extensive eventing system. It’s <a href="http://lostechies.com/derickbailey/2011/07/19/references-routing-and-the-event-aggregator-coordinating-views-in-backbone-js/">trivial</a> to add support for pub/sub in Backbone</li>
<li>Prototypes are instantiated with the <code>new</code> keyword, which some developers prefer</li>
<li>Agnostic about templating frameworks, however Underscore’s micro-templating is available by default.</li>
<li>Clear and flexible conventions for structuring applications. Backbone doesn’t force usage of all of its components and can work with only those needed.</li>
</ul>
<h3 id="used-by"><a href="#TOC">Used by</a></h3>
<p><em>Disqus</em></p>
<p>Disqus chose Backbone.js to power the latest version of their commenting widget. They felt it was the right choice for their distributed web app, given Backbone’s small footprint and ease of extensibility.</p>
<figure>
<img src="img/disqus.png"><figcaption></figcaption>
</figure>
<p><em>Khan Academy</em></p>
<p>Offering a web app that aims to provide free world-class education to anyone anywhere, Khan use Backbone to keep their frontend code both modular and organized.</p>
<figure>
<img src="img/khan-academy.png"><figcaption></figcaption>
</figure>
<p><em>MetaLab</em></p>
<p>MetaLab created Flow, a task management app for teams using Backbone. Their workspace uses Backbone to create task views, activities, accounts, tags and more.</p>
<figure>
<img src="img/flow.png"><figcaption></figcaption>
</figure>
<p><em>Walmart Mobile</em></p>
<p>Walmart chose Backbone to power their mobile web applications, creating two new extension frameworks in the process - Thorax and Lumbar. We’ll be discussing both of these later in the book.</p>
<figure>
<img src="img/walmart-mobile.png"><figcaption></figcaption>
</figure>
<p><em>AirBnb</em></p>
<p>Airbnb developed their mobile web app using Backbone and now use it across many of their products.</p>
<figure>
<img src="img/airbnb.png"><figcaption></figcaption>
</figure>
<p><em>Code School</em></p>
<p>Code School’s course challenge app is built from the ground up using Backbone, taking advantage of all the pieces it has to offer: routers, collections, models and complex event handling.</p>
<figure>
<img src="img/code-school.png"><figcaption></figcaption>
</figure>
<h1 id="backbone-basics"><a href="#TOC">Backbone Basics</a></h1>
<p>In this section, you’ll learn the essentials of Backbone’s models, views, collections, events, and routers. This isn’t by any means a replacement for the official documentation, but it will help you understand many of the core concepts behind Backbone before you start building applications using it.</p>
<h3 id="getting-setup"><a href="#TOC">Getting setup</a></h3>
<p>Before we dive into more code examples, let’s define some boilerplate markup you can use to specify the dependencies Backbone requires. This boilerplate can be reused in many ways with little to no alteration and will allow you to run code from examples with ease.</p>
<p>You can paste the following into your text editor of choice, replacing the commented line between the script tags with the JavaScript from any given example:</p>
<pre class="sourceCode html"><code class="sourceCode html"><span class="dt"><!DOCTYPE </span>HTML<span class="dt">></span>
<span class="kw"><html></span>
<span class="kw"><head></span>
<span class="kw"><meta</span><span class="ot"> charset=</span><span class="st">"UTF-8"</span><span class="kw">></span>
<span class="kw"><title></span>Title<span class="kw"></title></span>
<span class="kw"></head></span>
<span class="kw"><body></span>
<span class="kw"><script</span><span class="ot"> src=</span><span class="st">"https://ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js"</span><span class="kw">></script></span>
<span class="kw"><script</span><span class="ot"> type=</span><span class="st">"text/javascript"</span><span class="ot"> src=</span><span class="st">"http://documentcloud.github.com/underscore/underscore-min.js"</span><span class="kw">></script></span>
<span class="kw"><script</span><span class="ot"> type=</span><span class="st">"text/javascript"</span><span class="ot"> src=</span><span class="st">"http://documentcloud.github.com/backbone/backbone-min.js"</span><span class="kw">></script></span>
<span class="kw"><script</span><span class="ot"> type=</span><span class="st">"text/javascript"</span><span class="kw">></span>
<span class="co">// Your code goes here</span>
<span class="kw"></script></span>
<span class="kw"></body></span>
<span class="kw"></html></span></code></pre>
<p>You can then save and run the file in our browser of choice, such as Chrome or Firefox. Alternatively, if you prefer working with an online code editor, <a href="http://jsfiddle.net/jnf8B/">jsFiddle</a> and <a href="http://jsbin.com/iwiwox/1/edit">jsBin</a> versions of this boilerplate are also available.</p>
<p>Most examples can also be run directly from within the console in your browser’s developer tools, assuming you’ve loaded the boilerplate HTML page so that Backbone and it’s dependencies are available for use.</p>
<p>For Chrome, you can open up the DevTools via the Chrome menu in the top right hand corner: select <q>Tools > Developer Tools</q> or alternatively use the Control + Shift + I shortcut on Windows/Linux or Command + Option + I on Mac.</p>
<figure>
<img src="img/devtools.png"><figcaption></figcaption>
</figure>
<p>Next, switch to the Console tab, from where you can enter in and run any piece of JavaScript code by hitting the return key. You can also use the Console as a multi-line editor using the Ctrl + Enter shortcut to move from the end of one line to the start of another.</p>
<h2 id="models-1"><a href="#TOC">Models</a></h2>
<p>Backbone models contain data for an application as well as the logic around this data. For example, we can use a model to represent the concept of a todo item including its attributes like title (todo content) and completed (current state of the todo).</p>
<p>Models can be created by extending <code>Backbone.Model</code> as follows:</p>
<pre class="sourceCode javascript"><code class="sourceCode javascript"><span class="kw">var</span> Todo = <span class="kw">Backbone.Model</span>.<span class="fu">extend</span>({});
<span class="co">// We can then create our own concrete instance of a (Todo) model</span>
<span class="co">// with no values at all:</span>
<span class="kw">var</span> todo1 = <span class="kw">new</span> Todo();
<span class="co">// Following logs: {}</span>
<span class="kw">console</span>.<span class="fu">log</span>(<span class="kw">JSON</span>.<span class="fu">stringify</span>(todo1));
<span class="co">// or with some arbitrary data:</span>
<span class="kw">var</span> todo2 = <span class="kw">new</span> Todo({
<span class="dt">title</span>: <span class="ch">'Check the attributes of both model instances in the console.'</span>,
<span class="dt">completed</span>: <span class="kw">true</span>
});
<span class="co">// Following logs: {"title":"Check the attributes of both model instances in the console.","completed":true}</span>
<span class="kw">console</span>.<span class="fu">log</span>(<span class="kw">JSON</span>.<span class="fu">stringify</span>(todo2));</code></pre>
<h4 id="initialization"><a href="#TOC">Initialization</a></h4>
<p>The <code>initialize()</code> method is called when a new instance of a model is created. Its use is optional; however you’ll see why it’s good practice to use it below.</p>
<pre class="sourceCode javascript"><code class="sourceCode javascript"><span class="kw">var</span> Todo = <span class="kw">Backbone.Model</span>.<span class="fu">extend</span>({
<span class="dt">initialize</span>: <span class="kw">function</span>(){
<span class="kw">console</span>.<span class="fu">log</span>(<span class="ch">'This model has been initialized.'</span>);
}
});
<span class="kw">var</span> myTodo = <span class="kw">new</span> Todo();
<span class="co">// Logs: This model has been initialized.</span></code></pre>
<p><strong>Default values</strong></p>
<p>There are times when you want your model to have a set of default values (e.g., in a scenario where a complete set of data isn’t provided by the user). This can be set using a property called <code>defaults</code> in your model.</p>
<pre class="sourceCode javascript"><code class="sourceCode javascript"><span class="kw">var</span> Todo = <span class="kw">Backbone.Model</span>.<span class="fu">extend</span>({
<span class="co">// Default todo attribute values</span>
<span class="dt">defaults</span>: {
<span class="dt">title</span>: <span class="ch">''</span>,
<span class="dt">completed</span>: <span class="kw">false</span>
}
});
<span class="co">// Now we can create our concrete instance of the model</span>
<span class="co">// with default values as follows:</span>
<span class="kw">var</span> todo1 = <span class="kw">new</span> Todo();
<span class="co">// Following logs: {"title":"","completed":false}</span>
<span class="kw">console</span>.<span class="fu">log</span>(<span class="kw">JSON</span>.<span class="fu">stringify</span>(todo1));
<span class="co">// Or we could instantiate it with some of the attributes (e.g., with custom title):</span>
<span class="kw">var</span> todo2 = <span class="kw">new</span> Todo({
<span class="dt">title</span>: <span class="ch">'Check attributes of the logged models in the console.'</span>
});
<span class="co">// Following logs: {"title":"Check attributes of the logged models in the console.","completed":false}</span>
<span class="kw">console</span>.<span class="fu">log</span>(<span class="kw">JSON</span>.<span class="fu">stringify</span>(todo2));
<span class="co">// Or override all of the default attributes:</span>
<span class="kw">var</span> todo3 = <span class="kw">new</span> Todo({
<span class="dt">title</span>: <span class="ch">'This todo is done, so take no action on this one.'</span>,
<span class="dt">completed</span>: <span class="kw">true</span>
});
<span class="co">// Following logs: {"title":"This todo is done, so take no action on this one.","completed":true} </span>
<span class="kw">console</span>.<span class="fu">log</span>(<span class="kw">JSON</span>.<span class="fu">stringify</span>(todo3));</code></pre>
<h4 id="getters-setters"><a href="#TOC">Getters & Setters</a></h4>
<p><strong>Model.get()</strong></p>
<p><code>Model.get()</code> provides easy access to a model’s attributes.</p>
<pre class="sourceCode javascript"><code class="sourceCode javascript"><span class="kw">var</span> Todo = <span class="kw">Backbone.Model</span>.<span class="fu">extend</span>({
<span class="co">// Default todo attribute values</span>
<span class="dt">defaults</span>: {
<span class="dt">title</span>: <span class="ch">''</span>,
<span class="dt">completed</span>: <span class="kw">false</span>
}
});
<span class="kw">var</span> todo1 = <span class="kw">new</span> Todo();
<span class="kw">console</span>.<span class="fu">log</span>(<span class="kw">todo1</span>.<span class="fu">get</span>(<span class="ch">'title'</span>)); <span class="co">// empty string</span>
<span class="kw">console</span>.<span class="fu">log</span>(<span class="kw">todo1</span>.<span class="fu">get</span>(<span class="ch">'completed'</span>)); <span class="co">// false</span>
<span class="kw">var</span> todo2 = <span class="kw">new</span> Todo({
<span class="dt">title</span>: <span class="st">"Retrieved with model's get() method."</span>,
<span class="dt">completed</span>: <span class="kw">true</span>
});
<span class="kw">console</span>.<span class="fu">log</span>(<span class="kw">todo2</span>.<span class="fu">get</span>(<span class="ch">'title'</span>)); <span class="co">// Retrieved with model's get() method.</span>
<span class="kw">console</span>.<span class="fu">log</span>(<span class="kw">todo2</span>.<span class="fu">get</span>(<span class="ch">'completed'</span>)); <span class="co">// true</span></code></pre>
<p>If you need to read or clone all of a model’s data attributes, use its <code>toJSON()</code> method. This method returns a copy of the attributes as an object (not a JSON string despite its name). (When <code>JSON.stringify()</code> is passed an object with a <code>toJSON()</code> method, it stringifies the return value of <code>toJSON()</code> instead of the original object. The examples in the previous section took advantage of this feature when they called <code>JSON.stringify()</code> to log model instances.)</p>
<pre class="sourceCode javascript"><code class="sourceCode javascript"><span class="kw">var</span> Todo = <span class="kw">Backbone.Model</span>.<span class="fu">extend</span>({
<span class="co">// Default todo attribute values</span>
<span class="dt">defaults</span>: {
<span class="dt">title</span>: <span class="ch">''</span>,
<span class="dt">completed</span>: <span class="kw">false</span>
}
});
<span class="kw">var</span> todo1 = <span class="kw">new</span> Todo();
<span class="kw">var</span> todo1Attributes = <span class="kw">todo1</span>.<span class="fu">toJSON</span>();
<span class="co">// Following logs: {"title":"","completed":false} </span>
<span class="kw">console</span>.<span class="fu">log</span>(todo1Attributes);
<span class="kw">var</span> todo2 = <span class="kw">new</span> Todo({
<span class="dt">title</span>: <span class="st">"Try these examples and check results in console."</span>,
<span class="dt">completed</span>: <span class="kw">true</span>
});
<span class="co">// logs: {"title":"Try these examples and check results in console.","completed":true}</span>
<span class="kw">console</span>.<span class="fu">log</span>(<span class="kw">todo2</span>.<span class="fu">toJSON</span>());</code></pre>
<p><strong>Model.set()</strong></p>
<p><code>Model.set()</code> sets a hash containing one or more attributes on the model. When any of these attributes alter the state of the model, a <q>change</q> event is triggered on it. Change events for each attribute are also triggered and can be bound to (e.g <code>change:name</code>, <code>change:age</code>).</p>
<pre class="sourceCode javascript"><code class="sourceCode javascript"><span class="kw">var</span> Todo = <span class="kw">Backbone.Model</span>.<span class="fu">extend</span>({
<span class="co">// Default todo attribute values</span>
<span class="dt">defaults</span>: {
<span class="dt">title</span>: <span class="ch">''</span>,
<span class="dt">completed</span>: <span class="kw">false</span>
}
});
<span class="co">// Setting the value of attributes via instantiation</span>
<span class="kw">var</span> myTodo = <span class="kw">new</span> Todo({
<span class="dt">title</span>: <span class="st">"Set through instantiation."</span>
});
<span class="kw">console</span>.<span class="fu">log</span>(<span class="ch">'Todo title: '</span> + <span class="kw">myTodo</span>.<span class="fu">get</span>(<span class="ch">'title'</span>)); <span class="co">// Todo title: Set through instantiation.</span>
<span class="kw">console</span>.<span class="fu">log</span>(<span class="ch">'Completed: '</span> + <span class="kw">myTodo</span>.<span class="fu">get</span>(<span class="ch">'completed'</span>)); <span class="co">// Completed: false</span>
<span class="co">// Set single attribute value at a time through Model.set():</span>
<span class="kw">myTodo</span>.<span class="fu">set</span>(<span class="st">"title"</span>, <span class="st">"Title attribute set through Model.set()."</span>);
<span class="kw">console</span>.<span class="fu">log</span>(<span class="ch">'Todo title: '</span> + <span class="kw">myTodo</span>.<span class="fu">get</span>(<span class="ch">'title'</span>)); <span class="co">// Todo title: Title attribute set through Model.set().</span>
<span class="kw">console</span>.<span class="fu">log</span>(<span class="ch">'Completed: '</span> + <span class="kw">myTodo</span>.<span class="fu">get</span>(<span class="ch">'completed'</span>)); <span class="co">// Completed: false</span>
<span class="co">// Set map of attributes through Model.set():</span>
<span class="kw">myTodo</span>.<span class="fu">set</span>({
<span class="dt">title</span>: <span class="st">"Both attributes set through Model.set()."</span>,
<span class="dt">completed</span>: <span class="kw">true</span>
});
<span class="kw">console</span>.<span class="fu">log</span>(<span class="ch">'Todo title: '</span> + <span class="kw">myTodo</span>.<span class="fu">get</span>(<span class="ch">'title'</span>)); <span class="co">// Todo title: Both attributes set through Model.set().</span>
<span class="kw">console</span>.<span class="fu">log</span>(<span class="ch">'Completed: '</span> + <span class="kw">myTodo</span>.<span class="fu">get</span>(<span class="ch">'completed'</span>)); <span class="co">// Completed: true</span></code></pre>
<p><strong>Direct access</strong></p>
<p>Models expose an <code>.attributes</code> attribute which represents an internal hash containing the state of that model. This is generally in the form of a JSON object similar to the model data you might find on the server but can take other forms.</p>
<p>Setting values through the <code>.attributes</code> attribute on a model bypasses triggers bound to the model. Additionally you can pass <code>{silent: true}</code>, which silences individual <q>change:attr</q> events entirely, but can build up and then hit in unexpected ways later on.</p>
<p>Remember where possible it is best practice to use <code>Model.set()</code>, or direct instantiation as explained earlier.</p>
<h4 id="listening-for-changes-to-your-model"><a href="#TOC">Listening for changes to your model</a></h4>
<p>If you want to receive a notification when a Backbone model changes you can bind a listener to the model for its change event. A convenient place to add listeners is in the <code>initialize()</code> function as shown below:</p>
<pre class="sourceCode javascript"><code class="sourceCode javascript"><span class="kw">var</span> Todo = <span class="kw">Backbone.Model</span>.<span class="fu">extend</span>({
<span class="co">// Default todo attribute values</span>
<span class="dt">defaults</span>: {
<span class="dt">title</span>: <span class="ch">''</span>,
<span class="dt">completed</span>: <span class="kw">false</span>
},
<span class="dt">initialize</span>: <span class="kw">function</span>(){
<span class="kw">console</span>.<span class="fu">log</span>(<span class="ch">'This model has been initialized.'</span>);
<span class="kw">this</span>.<span class="fu">on</span>(<span class="ch">'change'</span>, <span class="kw">function</span>(){
<span class="kw">console</span>.<span class="fu">log</span>(<span class="ch">'- Values for this model have changed.'</span>);
});
}
});
<span class="kw">var</span> myTodo = <span class="kw">new</span> Todo();
<span class="kw">myTodo</span>.<span class="fu">set</span>(<span class="ch">'title'</span>, <span class="ch">'The listener is triggered whenever an attribute value changes.'</span>);
<span class="kw">console</span>.<span class="fu">log</span>(<span class="ch">'Title has changed: '</span> + <span class="kw">myTodo</span>.<span class="fu">get</span>(<span class="ch">'title'</span>));
<span class="kw">myTodo</span>.<span class="fu">set</span>(<span class="ch">'completed'</span>, <span class="kw">true</span>);
<span class="kw">console</span>.<span class="fu">log</span>(<span class="ch">'Completed has changed: '</span> + <span class="kw">myTodo</span>.<span class="fu">get</span>(<span class="ch">'completed'</span>));
<span class="kw">myTodo</span>.<span class="fu">set</span>({
<span class="dt">title</span>: <span class="ch">'Changing more than one attribute at the same time only triggers the listener once.'</span>,
<span class="dt">completed</span>: <span class="kw">true</span>
});
<span class="co">// Above logs:</span>
<span class="co">// This model has been initialized.</span>
<span class="co">// - Values for this model have changed.</span>
<span class="co">// Title has changed: The listener is triggered whenever an attribute value changes.</span>
<span class="co">// - Values for this model have changed.</span>
<span class="co">// Completed has changed: true</span>
<span class="co">// - Values for this model have changed.</span></code></pre>
<p>You can also listen for changes to individual attributes in a Backbone model. In the following example, we log a message whenever a specific attribute (the title of our Todo model) is altered.</p>
<pre class="sourceCode javascript"><code class="sourceCode javascript"><span class="kw">var</span> Todo = <span class="kw">Backbone.Model</span>.<span class="fu">extend</span>({
<span class="co">// Default todo attribute values</span>
<span class="dt">defaults</span>: {
<span class="dt">title</span>: <span class="ch">''</span>,
<span class="dt">completed</span>: <span class="kw">false</span>
},
<span class="dt">initialize</span>: <span class="kw">function</span>(){
<span class="kw">console</span>.<span class="fu">log</span>(<span class="ch">'This model has been initialized.'</span>);
<span class="kw">this</span>.<span class="fu">on</span>(<span class="ch">'change:title'</span>, <span class="kw">function</span>(){
<span class="kw">console</span>.<span class="fu">log</span>(<span class="ch">'Title value for this model has changed.'</span>);
});
},
<span class="dt">setTitle</span>: <span class="kw">function</span>(newTitle){
<span class="kw">this</span>.<span class="fu">set</span>({ <span class="dt">title</span>: newTitle });
}
});
<span class="kw">var</span> myTodo = <span class="kw">new</span> Todo();
<span class="co">// Both of the following changes trigger the listener:</span>
<span class="kw">myTodo</span>.<span class="fu">set</span>(<span class="ch">'title'</span>, <span class="ch">'Check what\'s logged.'</span>);
<span class="kw">myTodo</span>.<span class="fu">setTitle</span>(<span class="ch">'Go fishing on Sunday.'</span>);
<span class="co">// But, this change type is not observed, so no listener is triggered:</span>
<span class="kw">myTodo</span>.<span class="fu">set</span>(<span class="ch">'completed'</span>, <span class="kw">true</span>);
<span class="kw">console</span>.<span class="fu">log</span>(<span class="ch">'Todo set as completed: '</span> + <span class="kw">myTodo</span>.<span class="fu">get</span>(<span class="ch">'completed'</span>));
<span class="co">// Above logs:</span>
<span class="co">// This model has been initialized.</span>
<span class="co">// Title value for this model has changed.</span>
<span class="co">// Title value for this model has changed.</span>
<span class="co">// Todo set as completed: true</span></code></pre>
<h4 id="validation"><a href="#TOC">Validation</a></h4>
<p>Backbone supports model validation through <code>model.validate()</code>, which allows checking the attribute values for a model prior to setting them. Validation by default occurs when the model is persisted using the <code>.save()</code> method or when <code>.set()</code> is called if <code>{validate:true}</code> is passed as an argument.</p>
<p>Validation functions can be as simple or complex as necessary. If the attributes provided are valid, nothing should be returned from <code>.validate()</code>. If they are invalid, an error value should be returned instead.</p>
<p>Should an error be returned:</p>
<ul>
<li>An <code>invalid</code> event will triggered, setting the <code>validationError</code> property on the model with the value which is returned by this method.</li>
<li><code>.save()</code> will not continue and the attributes of the model will not be modified on the server</li>
</ul>
<p>A basic validation example can be seen below:</p>
<pre class="sourceCode javascript"><code class="sourceCode javascript"><span class="kw">var</span> Todo = <span class="kw">Backbone.Model</span>.<span class="fu">extend</span>({
<span class="dt">defaults</span>: {
<span class="dt">completed</span>: <span class="kw">false</span>
},