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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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<body>
<p>
<h1>Developing Backbone.js Applications</h1>
<h3>By Addy Osmani <a href="http://twitter.com/addyosmani">@addyosmani</a></h3>
</p>
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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="#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-backbone.js">MVC & Backbone.js</a></li>
<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="#mvc-in-the-browser">MVC In The Browser</a></li>
<li><a href="#simple-javascript-mvc-implementation">Simple JavaScript MVC Implementation</a><ul>
<li><a href="#event-system">Event System</a></li>
<li><a href="#models">Models</a></li>
<li><a href="#views">Views</a></li>
<li><a href="#controllers">Controllers</a></li>
<li><a href="#practical-usage">Practical Usage</a></li>
</ul></li>
<li><a href="#imlementation-specifics">Imlementation Specifics</a><ul>
<li><a href="#notes-on-model">Notes on Model</a></li>
<li><a href="#notes-on-view">Notes on View</a></li>
<li><a href="#notes-on-controller">Notes on Controller</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">Delving deeper</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>
</ul></li>
</ul></li>
<li><a href="#the-internals">The Internals</a><ul>
<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="#underscore-utility-functions">Underscore utility functions</a></li>
<li><a href="#chainable-api">Chainable API</a></li>
</ul></li>
<li><a href="#events">Events</a></li>
<li><a href="#routers">Routers</a><ul>
<li><a href="#is-there-a-limit-to-the-number-of-routers-i-should-be-using">Is there a limit to the number of routers I should be using?</a></li>
<li><a href="#backbone.history">Backbone.history</a></li>
<li><a href="#backbones-sync-api">Backbone’s Sync API</a></li>
<li><a href="#conflict-management">Conflict Management</a></li>
</ul></li>
<li><a href="#inheritance-mixins">Inheritance & Mixins</a><ul>
<li><a href="#backbone-super">Backbone-Super</a></li>
</ul></li>
<li><a href="#dependencies">Dependencies</a><ul>
<li><a href="#dom-manipulation">DOM Manipulation</a></li>
<li><a href="#utilities">Utilities</a></li>
<li><a href="#restful-persistence">RESTFul persistence</a></li>
<li><a href="#routing">Routing</a></li>
</ul></li>
<li><a href="#namespacing">Namespacing</a><ul>
<li><a href="#what-is-namespacing">What is namespacing?</a></li>
</ul></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="#index">Index</a></li>
<li><a href="#application-html">Application HTML</a></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="#setup">Setup</a></li>
<li><a href="#in-action">In action</a></li>
<li><a href="#templates">Templates</a></li>
<li><a href="#in-action-1">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="#conclusions">Conclusions</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="#part-1">Part 1</a><ul>
<li><a href="#setting-up">Setting up</a></li>
</ul></li>
<li><a href="#part-2">Part 2</a><ul>
<li><a href="#adding-models">Adding models</a></li>
<li><a href="#removing-models">Removing models</a></li>
<li><a href="#summary-1">Summary</a></li>
</ul></li>
<li><a href="#part-2.5">Part 2.5</a><ul>
<li><a href="#installing-node-modules">Installing node modules</a></li>
<li><a href="#create-directory-structure">Create directory structure</a></li>
<li><a href="#create-a-simple-web-server">Create a simple web server</a></li>
<li><a href="#connect-to-database">Connect to database</a></li>
</ul></li>
<li><a href="#part-3">Part 3</a><ul>
<li><a href="#summary-2">Summary</a></li>
</ul></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">Backbone Boilerplate</a></li>
<li><a href="#grunt-bbb">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="#conclusions-1">Conclusions</a></li>
<li><a href="#related-tools-projects">Related Tools & Projects</a></li>
</ul></li>
<li><a href="#common-problems-solutions">Common Problems & Solutions</a><ul>
<li><a href="#nesting-what-is-the-best-approach-for-rendering-and-appending-sub-views-in-backbone.js">Nesting: What is the best approach for rendering and appending Sub-Views in Backbone.js?</a></li>
<li><a href="#what-is-the-best-way-to-manage-models-in-nested-views">What is the best way to manage models in nested Views?</a></li>
<li><a href="#is-it-possible-to-have-one-backbone.js-view-trigger-updates-in-other-views">Is it possible to have one Backbone.js View trigger updates in other Views?</a></li>
<li><a href="#how-would-one-render-a-parent-view-from-one-of-its-children">How would one render a Parent View from one of its Children?</a></li>
<li><a href="#how-do-you-cleanly-dispose-views-to-avoid-memory-leaks">How do you cleanly dispose Views to avoid memory leaks?</a></li>
<li><a href="#how-does-one-handle-view-disposal-on-a-parent-or-child-view">How does one handle View disposal on a Parent or Child View?</a></li>
<li><a href="#whats-the-best-way-to-combine-or-append-views-to-each-other">What’s the best way to combine or append Views to each other?</a></li>
<li><a href="#better-model-property-validation">Better Model Property Validation</a></li>
</ul></li>
<li><a href="#backbone-extensions">Backbone Extensions</a><ul>
<li><a href="#backbone.marionette">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="#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="#writing-amd-modules-with-requirejs">Writing AMD modules with RequireJS</a><ul>
<li><a href="#alternate-syntax">Alternate syntax</a></li>
</ul></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>
<li><a href="#optimize-and-build-a-backbone.js-javascript-application-with-requirejs-using-packages">Optimize and Build a Backbone.js JavaScript application with RequireJS using Packages</a><ul>
<li><a href="#file-organization">File organization</a></li>
<li><a href="#build-profile-to-optimize-modular-dependencies-with-code-organized-in-packages">Build profile to optimize modular dependencies with code organized in packages</a></li>
<li><a href="#a-quick-note-on-code-standards">A quick note on code standards</a></li>
<li><a href="#common-pitfall-when-organizing-code-in-modules">Common Pitfall when organizing code in modules</a></li>
<li><a href="#executing-the-build-with-r.js">Executing the Build with r.js</a></li>
</ul></li>
<li><a href="#exercise-building-a-modular-backbone-app-with-amd-requirejs">Exercise: Building a modular Backbone app with AMD & RequireJS</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>
</ul></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="#decoupling-backbone-with-the-mediator-and-facade-patterns">Decoupling Backbone with the Mediator and Facade Patterns</a><ul>
<li><a href="#summary-3">Summary</a></li>
<li><a href="#exercise">Exercise</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="#thorax-1"><a name="thorax">Thorax</a></a><ul>
<li><a href="#view-helper">view helper</a></li>
<li><a href="#creating-new-view-helpers">Creating new View helpers</a></li>
</ul></li>
</ul></li>
<li><a href="#mobile-applications">Mobile Applications</a><ul>
<li><a href="#backbone-jquery-mobile">Backbone & jQuery Mobile</a><ul>
<li><a href="#resolving-the-routing-conflicts">Resolving the routing conflicts</a></li>
<li><a href="#exercise-a-backbone-require.jsamd-app-with-jquery-mobile">Exercise: A Backbone, Require.js/AMD app with jQuery Mobile</a></li>
<li><a href="#getting-started-1">Getting started</a></li>
<li><a href="#jquery-mobile-going-beyond-mobile-application-development">jQuery Mobile: Going beyond mobile application development</a></li>
</ul></li>
</ul></li>
<li><a href="#unit-testing">Unit Testing</a><ul>
<li><a href="#unit-testing-backbone-applications-with-jasmine">Unit Testing Backbone Applications With Jasmine</a></li>
<li><a href="#introduction-2">Introduction</a></li>
<li><a href="#jasmine">Jasmine</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-setup">Getting setup</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></li>
<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>
<li><a href="#conclusions-2">Conclusions</a></li>
<li><a href="#exercise-1">Exercise</a></li>
<li><a href="#further-reading-1">Further reading</a></li>
<li><a href="#unit-testing-backbone-applications-with-qunit-and-sinonjs">Unit Testing Backbone Applications With QUnit And SinonJS</a></li>
<li><a href="#introduction-3">Introduction</a></li>
</ul></li>
<li><a href="#qunit">QUnit</a><ul>
<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="#matching-arguments-test-a-spy-was-called-with-a-specific-set-of-arguments">Matching arguments: test a spy was called with a specific set of arguments:</a></li>
<li><a href="#stricter-argument-matching-test-a-spy-was-called-at-least-once-with-specific-arguments-and-no-others">Stricter argument matching: test a spy was called at least once with specific arguments and no others:</a></li>
<li><a href="#testing-call-order-testing-if-a-spy-was-called-before-or-after-another-spy">Testing call order: testing if a spy was called before or after another spy:</a></li>
<li><a href="#match-execution-counts-test-a-spy-was-called-a-specific-number-of-times">Match execution counts: test a spy was called a specific number of times:</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-2">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="#event">Event</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-3">Conclusions</a><ul>
<li><a href="#notes">Notes</a></li>
</ul></li>
<li><a href="#appendix">Appendix</a><ul>
<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>
</ul></li>
</ul>
</nav>
<h2 id="prelude"><a href="#TOC">Prelude</a></h2>
<figure>
<img src="img/logo.jpg"><figcaption></figcaption>
</figure>
<p>Welcome to my (in-progress) book about the <a href="http://documentcloud.github.com/backbone/">Backbone.js</a> library for structuring JavaScript applications. It’s 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.</p>
<p>I’m very pleased to announce that this book will be out in physical form (once complete) via <a href="http://oreilly.com">O’Reilly Media</a>. Readers will have the option of purchasing the latest version in either print or a number of digital formats then or can grab a recent version from this repository.</p>
<p>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. My extended thanks go out to <a href="https://github.com/jashkenas">Jeremy Ashkenas</a> for creating Backbone.js and <a href="https://github.com/addyosmani/backbone-fundamentals/contributors">these</a> members of the community for their assistance tweaking this project.</p>
<p>I hope you find this book helpful!</p>
<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>When writing a web application from scratch it can be easy to feel like we can get by simply relying on a DOM manipulation library (such as jQuery) and a handful of plugins. The challenge with this approach is that it doesn’t take long to get lost in a nested pile of callbacks and DOM elements without any real structure in place.</p>
<p>In short, you can end up with a pile of spaghetti code - code that is disorganized and difficult to follow. This type of code has no simple panacea, short of a rewrite that may end up costing both time and money to alleviate. Fortunately, there are ways to avoid this problem.</p>
<p>Modern JavaScript frameworks and libraries can assist with bringing structure and organization to our projects, improving how maintainable they are from the start. They build on the trials and tribulations of developers who have had to work around similar callback chaos as you have, providing solutions to many common problems by default.</p>
<p>With that, in "Developing Backbone.js Applications:, I and a number of other experienced authors will take you through a journey of learning how to improve your application structure using one such library - Backbone.js.</p>
<h3 id="what-is-mvc"><a href="#TOC">What Is MVC?</a></h3>
<p>The modern JavaScript frameworks I mentioned a moment ago 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 down 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 should notify anyone observing them about their current state (e.g Views).</li>
<li>Views are typically considered the User-interface in an application (e.g your markup and templates), but don’t have to be. They should know about the existence of Models in order to observe them, but don’t directly communicate with them.</li>
<li>Controllers handle the input (e.g clicks, user actions) in an application and Views can be considered as handling the output. When a Controller updates the state of a model (such as editing Todo note content), it doesn’t directly tell the View. This is what the observing nature of the View and Model relationship is for.</li>
</ul>
<p>JavaScript <q>MVC</q> frameworks that can help us structure our code don’t always strictly follow the above pattern. Some solutions will include the responsibility of the Controller in the View (e.g Backbone.js) whilst others add their own opinionated components into the mix as they feel this is more effective.</p>
<p>For this reason we refer to such frameworks as following the MV* pattern, that is, you’re likely to have a View and a Model, but more likely to have something else also included.</p>
<h3 id="what-is-backbone.js"><a href="#TOC">What is Backbone.js?</a></h3>
<figure>
<img src="img/backbonejsorg.png"><figcaption></figcaption>
</figure>
<p>Backbone.js is a lightweight JavaScript library for adding 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 or SPAs. To put it simply, these apps enable the browser to react to changes in data on the client-side without the need to completely load up all your markup from the server, meaning no complete page-refreshes are necessary.</p>
<p>Backbone.js is a mature, popular library at the time of writing and has both a large development community online as well as a wealth of plugins and extensions available to build upon it. It has been used to create non-trivial applications by companies such as Disqus, Walmart, SoundCloud and Foursquare.</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, such as Backbone.js.</p>
<p>At the outset, it isn’t terribly difficult to write an application framework that offers some opinionated way to avoid spaghetti code, however to say that it is equally as trivial to write something of the standard of 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 not only include many of 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 that will likely only be communicating with an API or back-end data service, where much of the heavy lifting for viewing or manipulating that data will be occurring in the browser, you may find a JavaScript MV* framework useful. Good examples of applications that fall into this category are GMail and Google Docs.</p>
<p>These 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. It’s trivial to switch between reading an email or document to writing one and you don’t need to ask the application to render the whole page again at all.</p>
<p>If, however, you’re building an application that still relies on the server for most of the heavy-lifting of Views/pages and you’re just using a little JavaScript or jQuery to make things a little 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>Does the following describe you?:</p>
<p>"I want something flexible which offers a minimalist solution to separating concerns in my application. It should support a persistence layer and RESTful sync, models, views (with controllers), event-driven communication, templating and routing. It should be imperative, allowing one to update the View when a model changes. I’d like some decisions about the architecture left up to me. Ideally, many large companies have used the solution to build non-trivial applications.</p>
<p>As I may be building something complex, I’d like there to be an active extension community around the framework that have already tried addressing larger problems (Marionette, Chaplin, Aura, Thorax). Ideally, there are also scaffolding tools (grunt-bbb, brunch) available for the solution."</p>
<p>If so, continue reading.</p>
<p>Backbone’s main benefits, regardless of your target platform or device, include helping:</p>
<ul>
<li>Organize the structure to your application</li>
<li>Simplify server-side persistence</li>
<li>Decouple the DOM from your page’s data</li>
<li>Model data, views and routers in a succinct manner</li>
<li>Provide DOM, model and collection synchronization</li>
</ul>
<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 a pull-request. It won’t take long and you’ll be helping other developers avoid problems you’ve run into before.</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 the routing problems with Backbone and jQuery Mobile and a lot more.</p>
<h1 id="fundamentals"><a href="#TOC">Fundamentals</a></h1>
<p>In this first chapter, we’re going to explore how frameworks like Backbone.js fit in the world of JavaScript application architecture. Classically, 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 come to client-side development.</p>
<p>Before exploring any JavaScript frameworks that assist in structuring applications, it can be useful to gain a basic understanding of architectural design patterns.</p>
<h3 id="mvc-backbone.js"><a href="#TOC">MVC & Backbone.js</a></h3>
<p>Design patterns are proven solutions to common development problems and can help guide us in adding more organization and structure to our applications. Patterns are also of great use as they reflect a set of practices which build upon the collective experience of skilled developers who have repeatedly solved similar problems.</p>
<p>In this section, we’re going to explore the MVC (Model-View-Controller) pattern and how it applies to Backbone.js.</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 the 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 what 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 were 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), doing something sensible with them.</li>
<li>The Observer pattern was relied upon for updating 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 Models 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 no 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 obey the web context.</p>
<p>A typical server-side MVC implementation has one MVC stack layered behind the singe point of entry. This single point of entry means that all HTTP requests, e.g. <code>http://www.example.com</code> or <code>http://www.example.com/whichever-page/</code> etc., are routed, by a server configuration, through one point or, to be bold, one file, e.g. <code>index.php</code>.</p>
<p>At that point, there would be an implementation of what we call the Front Controller pattern which, once it receives it, analyzes HTTP requests and decides which class (Controller) and method (Action) are to be invoked as a response to the request. Method is the name for a function and member is name for a variable when part of the class/object.</p>
<p>Once invoked the Controller takes over and passes to and/or fetches data from the appropriate Model for the Action in concern. After the Controller receives the data from Model it loads the view, which corresponds to the invoked Action, injects the data into it and returns the response to the user.</p>
<p>For example, let 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 sever 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 say, the Articles model and its <code>Articles::getEntry(43)</code> method (43 corresponding to <code>/43/</code> in URI) which would return the blog article data from database for edit. Afterwards, Article Controller would load (<code>article/edit</code>) view which would have logic for injecting the article’s data into the form for user to edit its content, title and other (meta) data. Once all this is done response is 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>. This time the request would go through the same Controller, but the Save Action (due to the <code>/save/</code> URI chunk), and invoked Articles Model would save edit article to the database with <code>Articles::saveEntry(43)</code> and redirect back to the <code>/article/edit/43</code> for further editing.</p>
<p>If the user requested <code>http://www.example.com/</code>:</p>
<p>On the server side the Front Controller would invoke default Controller and Action, e.g. Index Controller and its Index action. Within Index Action there would be a call to Articles model and its <code>Articles::getLastEntries(10)</code> method which would return last 10 blog posts. Afterwards, the Controller would load blog/index view which would have basic logic for listing last 10 blog posts.</p>
<p>We can see the larger picture of typical HTTP request lifecycle through the server side MVC in the picture below.</p>
<figure>
<img src="img/webmvcflow_bacic.png"><figcaption></figcaption>
</figure>
<p>Server receives a request and routes it through a single entry point. At the entry point, the Front Controller analyzes the request and based on it invokes the appropriate Action of the appropriate Controller. This process is called routing. The Action Model is asked to return and/or save submitted data. Model communicates with the data source (e.g. database or API etc.). 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.) with the supplied data. In the end, the response is returned to the user.</p>
<p>Demand for fast, complex and responsive Ajax powered web applications demanded a lot of this logic to be replicated on the client side. This meant a lot more code had to exist there. Eventually it brought us to the point that we needed 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>And, of course, JavaScript and browsers create another context which require that we bend or adjust the traditional MVC paradigm to fit it.</p>
<h3 id="mvc-in-the-browser"><a href="#TOC">MVC In The Browser</a></h3>
<p>In complex JavaScript web applications, aka Single Page Applications (SPA), all application responses (e.g. UI updates) to user inputs are done seemlessly on the client-side. Data fetching and persistence (e.g. saving to database on server) are done with Ajax in the background. For silky, slick and smooth user experiences, the code powering these interacions needs to be well thought out.</p>
<p>Through evolution, trial and error, and a lot of spaghetti and not so spaghetti-like code developers in the end developed on ideas of traditional MVC paradigm and brought the solution for structuring JavaScript code to the landscape of the SPAs through JavaScript MVC frameworks. JavaScript now has a number of MVC frameworks, including Ember.js, JavaScriptMVC, and of course Backbone.js.</p>
<p><strong>The problem</strong></p>
<p>A typical page in an SPA consists of smaller ingredients which, when looked at at a deeper level, represent logical entities, which involve specific data domains that should be represented in a particular way on the page.</p>
<p>A good example is basket in an e-commerce web application which would typically have a list of items added to it and presented to the user as box in top right corner of the page (see the picture).</p>
<figure>
<img src="img/wireframe_e_commerce.png"><figcaption></figcaption>
</figure>
<p>The basket has its data and representation of the data in HTML. This data and 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 sync the two. That often produced code that was not so well structured and easy to maintain. Bugs were easy to produce and they are even unavoidable.</p>
<p>Eventually, an elegant way to handle it was brought to the client side throught JavaScript MVC libraries.</p>
<p>Now, data is handled with a Model and its HTML representation with View. So, on Model changes the View is updated and vice versa. The Controller is the component that manages this synchronization. It sends update commands both ways, to the View to update itself based on the Model change (e.g. sync with database) and to the Model based on the View changes (e.g. new item dropped into the basket). This way offers a better separation of concerns and improved code structure is accomplished.</p>
<h3 id="simple-javascript-mvc-implementation"><a href="#TOC">Simple JavaScript MVC Implementation</a></h3>
<p>Let’s see a simple implementation of the MVC pattern and its usage to clarify some concepts - we’re going to call our little library Cranium.js.</p>
<p>To simplify a bit we will rely on <a href="http://underscorejs.org" title="Underscore.js">Underscore</a> for inheritance and templating (similar to Backbone).</p>
<h4 id="event-system"><a href="#TOC">Event System</a></h4>
<p>At the heart of our JavaScript MVC implementation is an <code>Event</code> system (object) based on the Publisher-Subscriber Pattern which makes it possible for MVC components to intercommunicate in an elegant, decoupled manner. Subscribers <q>listen</q> out for specific events of interest and react when Publishers broadcast these events.</p>
<p><code>Event</code> is inherited by the View and Model components. That way each of them can inform other component that event of the interest to them happened.</p>
<pre class="sourceCode javascript"><code class="sourceCode javascript"><span class="co">// cranium.js - Cranium.Events</span>
<span class="kw">var</span> Cranium = Cranium || {};
<span class="co">// Set DOM selection utility</span>
<span class="kw">var</span> $ = <span class="kw">document</span>.<span class="fu">querySelector</span>.<span class="fu">bind</span>(<span class="kw">document</span>) || <span class="kw">this</span>.<span class="fu">jQuery</span> || <span class="kw">this</span>.<span class="fu">Zepto</span>;
<span class="co">// Mix in to any object in order to provide it with custom events.</span>
<span class="kw">var</span> Events = <span class="kw">Cranium</span>.<span class="fu">Events</span> = {
<span class="co">// Keeps list of events and associated listeners</span>
<span class="dt">channels</span>: {},
<span class="co">// Counter</span>
<span class="dt">eventNumber</span>: <span class="dv">0</span>,
<span class="co">// Announce events and passes data to the listeners;</span>
<span class="dt">trigger</span>: <span class="kw">function</span> (events, data) {
<span class="kw">for</span> (<span class="kw">var</span> topic <span class="kw">in</span> <span class="kw">Cranium.Events</span>.<span class="fu">channels</span>){
<span class="kw">if</span> (<span class="kw">Cranium.Events.channels</span>.<span class="fu">hasOwnProperty</span>(topic)) {
<span class="kw">if</span> (<span class="kw">topic</span>.<span class="fu">split</span>(<span class="st">"-"</span>)[<span class="dv">0</span>] == events){
<span class="kw">Cranium.Events</span>.<span class="fu">channels</span>[topic](data) !== <span class="kw">false</span> || <span class="kw">delete</span> <span class="kw">Cranium.Events</span>.<span class="fu">channels</span>[topic];
}
}
}
},
<span class="co">// Registers an event type and its listener</span>
<span class="dt">on</span>: <span class="kw">function</span> (events, callback) {
<span class="kw">Cranium.Events</span>.<span class="fu">channels</span>[events + --<span class="kw">Cranium.Events</span>.<span class="fu">eventNumber</span>] = callback;
},
<span class="co">// Unregisters an event type and its listener</span>
<span class="dt">off</span>: <span class="kw">function</span>(topic) {
<span class="kw">delete</span> <span class="kw">Cranium.Events</span>.<span class="fu">channels</span>[topic];
}
};</code></pre>
<p>The Event system makes it possible for:</p>
<ul>
<li>for View to notify its subscribers of user interaction, like click or input in a form, to update/re-render its UI etc.</li>
<li>for Model once its data has changed to notify its Subscribers to update themselves (e.g. view to re-render to show accurate/updated data) etc.</li>
</ul>
<h4 id="models"><a href="#TOC">Models</a></h4>
<p>Models manage the (domain-specific) data for an application. They are concerned with neither the user-interface nor presentation layers, but instead represent structured data that an application may require. When a model changes (e.g when it is updated), it will typically notify its observers (Subscribers) that a change has occurred so that they may react accordingly.</p>
<p>Let’s see a simple implementation of the Model:</p>
<pre class="sourceCode javascript"><code class="sourceCode javascript"><span class="co">// cranium.js - Cranium.Model</span>
<span class="co">// Attributes represents data, model's properties.</span>
<span class="co">// These are to be passed at Model instantiation.</span>
<span class="co">// Also we are creating id for each Model instance </span>
<span class="co">// so that it can identify itself (e.g. on chage </span>
<span class="co">// announcements)</span>
<span class="kw">var</span> Model = <span class="kw">Cranium</span>.<span class="fu">Model</span> = <span class="kw">function</span> (attributes) {
<span class="kw">this</span>.<span class="fu">id</span> = <span class="kw">_</span>.<span class="fu">uniqueId</span>(<span class="ch">'model'</span>);
<span class="kw">this</span>.<span class="fu">attributes</span> = attributes || {};
};
<span class="co">// Getter (accessor) method;</span>
<span class="co">// returns named data item</span>
<span class="kw">Cranium.Model.prototype</span>.<span class="fu">get</span> = <span class="kw">function</span>(attrName) {
<span class="kw">return</span> <span class="kw">this</span>.<span class="fu">attributes</span>[attrName];
};
<span class="co">// Setter (mutator) method;</span>
<span class="co">// Set/mix in into model mapped data (e.g.{name: "John"})</span>
<span class="co">// and publishes the change event</span>
<span class="kw">Cranium.Model.prototype</span>.<span class="fu">set</span> = <span class="kw">function</span>(attrs){
<span class="kw">if</span> (<span class="kw">_</span>.<span class="fu">isObject</span>(attrs)) {
<span class="kw">_</span>.<span class="fu">extend</span>(<span class="kw">this</span>.<span class="fu">attributes</span>, attrs);
<span class="kw">this</span>.<span class="fu">change</span>(<span class="kw">this</span>.<span class="fu">attributes</span>);
}
<span class="kw">return</span> <span class="kw">this</span>;
};
<span class="co">// Returns clone of the Models data object </span>
<span class="co">// (used for view template rendering)</span>
<span class="kw">Cranium.Model.prototype</span>.<span class="fu">toJSON</span> = <span class="kw">function</span>(options) {
<span class="kw">return</span> <span class="kw">_</span>.<span class="fu">clone</span>(<span class="kw">this</span>.<span class="fu">attributes</span>);
};
<span class="co">// Helper function that announces changes to the Model</span>
<span class="co">// and passes the new data</span>
<span class="kw">Cranium.Model.prototype</span>.<span class="fu">change</span> = <span class="kw">function</span>(attrs){
<span class="kw">this</span>.<span class="fu">trigger</span>(<span class="kw">this</span>.<span class="fu">id</span> + <span class="ch">'update'</span>, attrs);
};
<span class="co">// Mix in Event system</span>
<span class="kw">_</span>.<span class="fu">extend</span>(<span class="kw">Cranium.Model</span>.<span class="fu">prototype</span>, <span class="kw">Cranium</span>.<span class="fu">Events</span>);</code></pre>
<h4 id="views"><a href="#TOC">Views</a></h4>
<p>Views are a visual representation of models that present a filtered view of their current state. A view typically observes a model and is notified when the model changes, allowing the view to update itself accordingly. Design pattern literature commonly refers to views as <q>dumb</q>, given that their knowledge of models and controllers in an application is limited.</p>
<p>Let’s explore Views a little further using a simple JavaScript example:</p>
<pre class="sourceCode javascript"><code class="sourceCode javascript"><span class="co">// DOM View</span>
<span class="kw">var</span> View = <span class="kw">Cranium</span>.<span class="fu">View</span> = <span class="kw">function</span> (options) {
<span class="co">// Mix in options object (e.g extending functionallity)</span>
<span class="kw">_</span>.<span class="fu">extend</span>(<span class="kw">this</span>, options);
<span class="kw">this</span>.<span class="fu">id</span> = <span class="kw">_</span>.<span class="fu">uniqueId</span>(<span class="ch">'view'</span>);
};
<span class="co">// Mix in Event system</span>
<span class="kw">_</span>.<span class="fu">extend</span>(<span class="kw">Cranium.View</span>.<span class="fu">prototype</span>, <span class="kw">Cranium</span>.<span class="fu">Events</span>);</code></pre>
<h4 id="controllers"><a href="#TOC">Controllers</a></h4>
<p>Controllers are an intermediary between models and views which are classically responsible for two tasks:</p>
<ul>
<li>they both update the view when the model changes and</li>
<li>update the model when the user manipulates the view.</li>
</ul>
<pre class="sourceCode javascript"><code class="sourceCode javascript"><span class="co">// cranium.js - Cranium.Controller</span>
<span class="co">// Controller tying together a model and view</span>
<span class="kw">var</span> Controller = <span class="kw">Cranium</span>.<span class="fu">Controller</span> = <span class="kw">function</span>(options){
<span class="co">// Mix in options object (e.g extending functionallity)</span>
<span class="kw">_</span>.<span class="fu">extend</span>(<span class="kw">this</span>, options);
<span class="kw">this</span>.<span class="fu">id</span> = <span class="kw">_</span>.<span class="fu">uniqueId</span>(<span class="ch">'controller'</span>);
<span class="kw">var</span> parts, selector, eventType;
<span class="co">// Parses Events object passed during the definition of the </span>
<span class="co">// controller and maps it to the defined method to handle it;</span>
<span class="kw">if</span>(<span class="kw">this</span>.<span class="fu">events</span>){
<span class="kw">_</span>.<span class="fu">each</span>(<span class="kw">this</span>.<span class="fu">events</span>, <span class="kw">function</span>(method, eventName){
parts = <span class="kw">eventName</span>.<span class="fu">split</span>(<span class="ch">'.'</span>);
selector = parts[<span class="dv">0</span>];
eventType = parts[<span class="dv">1</span>];
$(selector)[<span class="ch">'on'</span> + eventType] = <span class="kw">this</span>[method];
}.<span class="fu">bind</span>(<span class="kw">this</span>));
}
};</code></pre>
<h4 id="practical-usage"><a href="#TOC">Practical Usage</a></h4>
<p>HTML template for the primer that follows:</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"> class=</span><span class="st">"todo-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 %>>
<%= title %>
</div>
<span class="kw"></script></span>
<span class="kw"><script</span><span class="ot"> src=</span><span class="st">"underscore-min.js"</span><span class="kw">></script></span>
<span class="kw"><script</span><span class="ot"> src=</span><span class="st">"cranium.js"</span><span class="kw">></script></span>
<span class="kw"><script</span><span class="ot"> src=</span><span class="st">"example.js"</span><span class="kw">></script></span>
<span class="kw"></body></span>
<span class="kw"></html></span></code></pre>
<p>Cranium.js usage:</p>
<pre class="sourceCode javascript"><code class="sourceCode javascript">
<span class="co">// example.js - usage of Cranium MVC</span>
<span class="co">// And todo instance</span>
<span class="kw">var</span> todo1 = <span class="kw">new</span> <span class="kw">Cranium</span>.<span class="fu">Model</span>({
<span class="dt">title</span>: <span class="st">""</span>,
<span class="dt">completed</span>: <span class="st">""</span>
});
<span class="kw">console</span>.<span class="fu">log</span>(<span class="st">"First todo title - nothing set: "</span> + <span class="kw">todo1</span>.<span class="fu">get</span>(<span class="ch">'title'</span>));
<span class="kw">todo1</span>.<span class="fu">set</span>({<span class="dt">title</span>: <span class="st">"Do something"</span>});
<span class="kw">console</span>.<span class="fu">log</span>(<span class="st">"Its chagned now: "</span> + <span class="kw">todo1</span>.<span class="fu">get</span>(<span class="ch">'title'</span>));
<span class="co">// View instance</span>
<span class="kw">var</span> todoView = <span class="kw">new</span> <span class="kw">Cranium</span>.<span class="fu">View</span>({
<span class="co">// DOM element selector</span>
<span class="dt">el</span>: <span class="ch">'#todo'</span>,
<span class="co">// Todo template; Underscore temlating used</span>
<span class="dt">template</span>: <span class="kw">_</span>.<span class="fu">template</span>($(<span class="ch">'.todo-template'</span>).<span class="fu">innerHTML</span>),
<span class="dt">init</span>: <span class="kw">function</span> (model) {
<span class="kw">this</span>.<span class="fu">render</span>( <span class="kw">model</span>.<span class="fu">toJSON</span>() );
<span class="kw">this</span>.<span class="fu">on</span>(<span class="kw">model</span>.<span class="fu">id</span> + <span class="ch">'update'</span>, <span class="kw">this</span>.<span class="fu">render</span>.<span class="fu">bind</span>(<span class="kw">this</span>));
},
<span class="dt">render</span>: <span class="kw">function</span> (data) {
<span class="kw">console</span>.<span class="fu">log</span>(<span class="st">"View about to render."</span>);
$(<span class="kw">this</span>.<span class="fu">el</span>).<span class="fu">innerHTML</span> = <span class="kw">this</span>.<span class="fu">template</span>( data );
}
});
<span class="kw">var</span> todoController = <span class="kw">new</span> <span class="kw">Cranium</span>.<span class="fu">Controller</span>({
<span class="co">// Specify the model to update</span>
<span class="dt">model</span>: todo1,
<span class="co">// and the view to observe this model</span>
<span class="dt">view</span>: todoView,
<span class="dt">events</span>: {
<span class="st">"#todo.click"</span> : <span class="st">"toggleComplete"</span>
},
<span class="co">// Initialize everything</span>
<span class="dt">initialize</span>: <span class="kw">function</span> () {
<span class="kw">this</span>.<span class="fu">view</span>.<span class="fu">init</span>(<span class="kw">this</span>.<span class="fu">model</span>);
<span class="kw">return</span> <span class="kw">this</span>;
},
<span class="co">// Toggles the value of the todo in the Model</span>
<span class="dt">toggleComplete</span>: <span class="kw">function</span> () {
<span class="kw">var</span> completed = <span class="kw">todoController.model</span>.<span class="fu">get</span>(<span class="ch">'completed'</span>);
<span class="kw">console</span>.<span class="fu">log</span>(<span class="st">"Todo old 'completed' value?"</span>, completed);
<span class="kw">todoController.model</span>.<span class="fu">set</span>({ <span class="dt">completed</span>: (!completed) ? <span class="ch">'checked'</span>: <span class="ch">''</span> });
<span class="kw">console</span>.<span class="fu">log</span>(<span class="st">"Todo new 'completed' value?"</span>, <span class="kw">todoController.model</span>.<span class="fu">get</span>(<span class="ch">'completed'</span>));
<span class="kw">return</span> <span class="kw">this</span>;
}
});
<span class="co">// Let's kick start things off</span>
<span class="kw">todoController</span>.<span class="fu">initialize</span>();
<span class="kw">todo1</span>.<span class="fu">set</span>({ <span class="dt">title</span>: <span class="st">"Due to this change Model will notify View and it will re-render"</span>});</code></pre>
<h3 id="imlementation-specifics"><a href="#TOC">Imlementation Specifics</a></h3>
<h4 id="notes-on-model"><a href="#TOC">Notes on Model</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 also have single or multiple views observing it. A developer could create a single view that displayed all Model attributes, or might create three separate views to display each attribute. The important detail is that the model doesn’t care how these views are organized, it simply announces updates to its data as necessary. It does it through system like the Event System we used in our Cranium Framework.</p></li>
<li><p>It is not uncommon for modern MVC/MV* frameworks to provide a means to group models together. In Backbone, these groups are called <q>Collections</q>. Managing models in groups allows us to write application logic based on notifications from the group, should any model it contains change. This avoids the need to manually observe individual model instances. We’ll see this in action later in the book.</p></li>
<li><p>If you read older texts on MVC, you may come across a description of models as also managing application <q>state</q>. In JavaScript applications state has a specific meaning, typically referring to the current state of a view or sub-view on a user’s screen at a fixed time. State is a topic which is regularly discussed when looking at Single-page applications, where the concept of state needs to be simulated.</p></li>
</ul>
<h4 id="notes-on-view"><a href="#TOC">Notes on View</a></h4>
<ul>
<li><p>Users interact with views, which usually means reading and editing model data. For example, in our todo application example, todo model viewing might happen in a user interface in the list of all todo items. Within it each todo is rendered with their title and completed checkbox. Model editing could be done through an <q>edit</q> view where a user who has selected a specific todo could edit 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>el</code>.</p></li>
<li><p>We then add our <code>render()</code> callback as one of <code>Model</code> subscribers, so that through Event System it can trigger the view to update when the model changes.</p></li>
<li><p>You may wonder where user interaction comes into play here. When users click on todo element within the view, it’s not the view’s responsibility to know what to do next. A Controller makes this decision. In our implementation, this is achieved by adding an event listener to todo element which will delegate handling the click behavior back to the controller, passing the model information along with it in case it’s needed. The benefit of this architecture is that each component plays its own separate role in making the application function as needed.</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 Handlebars.js or Mustache) 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 {{title}}). Javascript template libraries typically accept data in JSON, and the grunt work of populating templates with data is taken care of by the framework itself. This has a several benefits, particularly when opting to store templates externally as this can let applications 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 however 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="notes-on-controller"><a href="#TOC">Notes on Controller</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 this 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 that 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 separation of concerns in MVC facilitates modularization of an application’s functionality and enables:</p>
<ul>
<li>Easier overall maintenance. When updates need to be made to the application it is clear whether the changes are data-centric, meaning changes to models and possibly controllers, or merely visual, meaning changes to views.</li>
<li>Decoupling models and views means that it’s straight-forward to write unit tests for business logic</li>
<li>Duplication of low-level model and controller code is eliminated across the application</li>
<li>Depending on the size of the application and separation of roles, this modularity allows developers responsible for core logic and developers working on the user-interfaces to work simultaneously</li>
</ul>
<h3 id="delving-deeper"><a href="#TOC">Delving deeper</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 (Pub/Sub), 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, JavaScript Design Patterns For Beginners if you would like to read into 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 to respond 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 grok how the framework expects 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 is better categorized under, 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>Used by large companies such as SoundCloud and Foursquare to build non-trivial applications</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. Backbone works well with libraries like Handlebars</li>
<li>Doesn’t support deeply nested models, though there are Backbone plugins such as <a href="https://github.com/PaulUithol/Backbone-relational">Backbone-relational</a> which can help</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>
<h1 id="the-internals"><a href="#TOC">The Internals</a></h1>
<p>In this section, you’ll learn the essentials of Backbone’s models, views, collections and routers, as well as about using namespacing to organize your code. This isn’t meant as a replacement for the official documentation, but it will help you understand many of the core concepts behind Backbone before you start building applications with it.</p>
<ul>
<li>Models</li>
<li>Collections</li>
<li>Routers</li>
<li>Views</li>
<li>Dependencies</li>
<li>Namespacing</li>
</ul>
<h2 id="models-1"><a href="#TOC">Models</a></h2>
<p>Backbone models contain interactive 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="kw">console</span>.<span class="fu">log</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 attributes property of the both model instances in the console.'</span>,
<span class="dt">completed</span>: <span class="kw">true</span>
});
<span class="kw">console</span>.<span class="fu">log</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();</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="kw">console</span>.<span class="fu">log</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 property of the logged models in the console.'</span>
});
<span class="kw">console</span>.<span class="fu">log</span>(todo2);
<span class="co">// Or with 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="kw">console</span>.<span class="fu">log</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. All attributes, regardless if default ones were passed through to the model on instantiation, are available for retrieval.</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 models 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 models 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. Despite the name it doesn’t return a JSON string but a copy of the attributes as an object. (<q>toJSON</q> is part of the JSON.stringify specification. Passing an object with a toJSON method makes it stringify the return value of that method instead of the object itself.)</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 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> allows us to pass attributes into an instance of our model. Attributes can either be set during initialization or at any time afterwards. Backbone uses Model.set() to know when to broadcast that a model’s data has changed.</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="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">// Set single attribute value at the 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="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">// 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="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>));</code></pre>
<p><strong>Direct access</strong></p>
<p>If you really need to access the attributes in a model’s instance directly, there is <code>Model.attributes</code>. But remember it is best practice to use Model.get(), Model.set() or direct instantiation as explained above.</p>
<h4 id="listening-for-changes-to-your-model"><a href="#TOC">Listening for changes to your model</a></h4>
<p>Any and all of the attributes in a Backbone model can have listeners bound to them which detect when their values change. Listeners can be added to the <code>initialize()</code> function:</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">'On each change of attribute values listener is triggered.'</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">'Listener is triggered for each change, not for change of the each attribute.'</span>,
<span class="ch">'complete'</span>: <span class="kw">true</span>
});</code></pre>
<p>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 have 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">// 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>));</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 them being set.</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, a custom error can be returned instead.</p>
<p>A basic example for validation 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">validate</span>: <span class="kw">function</span>(attribs){
<span class="kw">if</span>(<span class="kw">attribs</span>.<span class="fu">title</span> === undefined){
<span class="kw">return</span> <span class="st">"Remember to set a title for your todo."</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="st">"error"</span>, <span class="kw">function</span>(model, error){
<span class="kw">console</span>.<span class="fu">log</span>(error);
});
}
});
<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">'completed'</span>, <span class="kw">false</span>); <span class="co">// logs: Remember to set a title for your todo.</span></code></pre>
<p><strong>Note</strong>: Backbone passes the <code>attributes</code> object (attribs param in above example) by shallow copy to the <code>validate</code> function using the Underscore <code>_.extend</code> method. This means that it is not possible to change any Number, String or Boolean attribute but it <em>is</em> possible to change attributes of objects because they are passed by reference. As shallow copy doesn’t copy objects by implicitly copying them, but rather, by reference, one can change the attributes on those objects.</p>
<p>An example of this (by @fivetanley) is available <a href="http://jsfiddle.net/2NdDY/7/">here</a>.</p>
<h2 id="views-1"><a href="#TOC">Views</a></h2>
<p>Views in Backbone don’t contain the markup for your application, but rather they are there to support models by defining the logic for how they should be represented to the user. This is usually achieved using JavaScript templating (e.g. Mustache, jQuery-tmpl, etc.). A view’s <code>render()</code> function can be bound to a model’s <code>change()</code> event, allowing the view to always be up to date without requiring a full page refresh.</p>
<h4 id="creating-new-views"><a href="#TOC">Creating new views</a></h4>
<p>Similar to the previous sections, creating a new view is relatively straight-forward. To create a new View, simply extend <code>Backbone.View</code>. I’ll explain this code in detail below:</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>( $(<span class="ch">'#item-template'</span>).<span class="fu">html</span>() ),
<span class="dt">events</span>: {
<span class="ch">'dblclick label'</span>: <span class="ch">'edit'</span>,
<span class="ch">'keypress .edit'</span>: <span class="ch">'updateOnEnter'</span>,
<span class="ch">'blur .edit'</span>: <span class="ch">'close'</span>
},
<span class="co">// Re-render the titles of the todo item.</span>
<span class="dt">render</span>: <span class="kw">function</span>() {
<span class="kw">this</span>.$<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>() {