JavaScript Libraries: The Big Picture

JavaScript Libraries: The Big Picture Simon Willison XTech, 16th May 2007

• What problems do libraries solve? • An overview of the Big Four • ... what are the interesting ideas?

Personal bias

• I like JavaScript-the-language • So I won't be talking about frameworks that generate JavaScript code for you

“ The Web is the most hostile software engineering environment imaginable.” Douglas Crockford

The legacy of the browser wars

• The DOM API kind of sucks • Event handling is frequently broken • Ajax is inconsistent • You have to roll your own animation • Drag and drop is tricky • Co-ordinates are surprisingly hard • Internet Explorer leaks memory like a sieve

The Event model // Internet Explorer element.attachEvent('click', function() { alert(window.event); } ) // Everyone else element.addEventListener('click', function(ev) { alert(ev) }, false );

“The bad news: JavaScript is broken. The good news: It can be ﬁxed with more JavaScript!” Geek folk saying

The big four • The Dojo Toolkit • The Yahoo! User Interface Library • Prototype (and Script.aculo.us) • jQuery

The Dojo Toolkit

• Founded in 2004 • Originally uniﬁed from a bunch of older frameworks • Initial aim was to show that JavaScript / DHTML should be taken seriously • Enormous amount of smart technology

dojo.collections dojo.math dojo.crypto dojo.reﬂect dojo.date dojo.rpc dojo.dnd dojo.storage dojo.dom dojo.string dojo.event dojo.style dojo.io dojo.undo dojo.lang dojo.uri dojo.lfx dojo.widget dojo.logging dojo.xml http://www.ﬂickr.com/photos/aprillynn77/8818200/

dijit • The Dojo widget system • Create widgets programmatically, or use declarative markup <div dojoType=quot;dijit.TitlePanequot; label=quot;Terms and Conditionsquot; width=quot;200quot;> Text... </div>

The future today • Cross browser 2D drawing APIs • dojo.storage - store data ofﬂine • dojo.undo.browser - history management • The Dojo Ofﬂine Toolkit

The Yahoo! User Interface Library

YUI • Created at Yahoo!, BSD licensed • Designed for both creating new applications and integration with legacy code • Focused on browser issues; almost no functionality relating to JS language itself • Extensively tested and documented

controls calendar container autocomplete menu slider treeview dragdrop animation dom event connection utilities

YAHOO.util.Event.on(window, 'load', function() { var div = YAHOO.util.Dom.get('messages'); if (!div) { return; } setTimeout(function() { var anim = new YAHOO.util.Anim(div, { height: {to: 0}, opacity: {to: 0} }, 0.4); anim.animate(); anim.onComplete.subscribe(function() { div.parentNode.removeChild(div); }); }, 2000); });

Download Get the latest version—1.5.1 Learn Prototype is a JavaScript Framework that aims to Online documentation and resources. ease development of dynamic web applications. Discuss Featuring a unique, easy-to-use toolkit for class-driven development and the nicest Ajax library around, Prototype Mailing list and IRC is quickly becoming the codebase of choice for web application developers everywhere. Contribute Prototype and Script.aculo.us Submit patches and report bugs. Prototype and script.aculo.us: The quot;Bungee bookquot; has landed! Who's using Prototype? Meet the developers Core team member Christophe Porteneuve has been hard at work for the past few months tracking

• Integrated with Ruby on Rails, but can be used separately as well • Small, readable codebase - Prototype is just 3,000 lines • Makes JavaScript behave more like Ruby • This is a dual-edged sword

$$('#bmarks li').each(function(li){ Event.observe(li, 'click', function(e) { this.style.backgroundColor = 'yellow'; }.bindAsEventListener(li)); });

Script.aculo.us • Wizzy extension for Prototype • Huge collection of packaged effects • AutoComplete, Slider, InPlaceEditor controls • Drag and drop • Easier DOM building

jQuery

$(document).ready(function(){ $(quot;aquot;).addClass('hidden').click( function() { $(this).hide(quot;slowquot;); return false; }); ); });

It’s not a gimmick! • API designed around “chaining” • Built in support for onContentLoaded • Outstanding node selection • CSS 3, XPath and custom extensions • Small core library, smart plugin mechanism • visualjquery.com/ offers the best docs

Playing well with others

“Namespaces are one honking great idea -- let's do more of those!” Tim Peters, “The Zen of Python” python -c quot;import thisquot;

Prototype var moo = $('moo'); ['foo', 'bar'].each(function(id) { // ... }); quot;This is a stringquot;.dasherize() Object.toJSON({foo: 'bar'}

YUI YAHOO.util.Event.on( YAHOO.util.Dom.get('foo'), 'click', function(ev) { YAHOO.util.Event.stopEvent(ev); // ... } );

YUI idiom var $E = YAHOO.util.Event; var $D = YAHOO.util.Dom; $E.on( $D.get('foo'), 'click', function(ev) { $E.stopEvent(ev); // ... } );

jQuery • Everything it does is encapsulated in the jQuery function / object • $(...) is just a shortcut for jQuery(...) • If it exists, the original $ function is stashed away in jQuery._$ • You can restore it with jQuery.noConﬂict()

jQuery.noConﬂict() <script src=quot;prototype.jsquot;></script> <script src=quot;jquery.jsquot;></script> <script> jQuery.noConflict(); jQuery(function($) { $('div.panel').hide(); // ... }); </script>

Progressive enhancement

http://www.neighbourhoodﬁxit.com/

Some neat ideas

Interaction Design Patterns

Smart node selection • Progressive enhancement inevitably starts out by selecting existing nodes • jQuery is based entirely around node selection • Prototype has node selection as a key API • YUI and Dojo just have getElementsByClassName • YUI-ext offers smarter selections for YUI

Smarter Ajax • Prototype makes it easy to set a callback for when ANY Ajax request completes... useful for loading status icons • Ajax.Updater can extract and execute <script> blocks in HTML fragments • Great for unobtrusively enhancing elements that have just been added to the page

Self-adjusting animations • You can roll your own animations in JavaScript using setTimeout and setInterval... • ... but the time taken for a animation will vary depending on browser performance • Smarter animations adjust their framerate to compensate for browser performance • All four libraries do this

DSLs for animation var anim = new YAHOO.util.Anim('el', { opacity: {to: 0.5}, height: {to: 0}, fontSize: { from: 100, to: 50, unit: '%' } }, 1); anim.animate();

XPath optimisations • Mozilla and Opera offer fast XPath lookups through document.evaluate(...) • Dojo can use this for getElementsByClass() • Prototype redeﬁnes getElementsBySelector to use XPath

Miniﬁcation • All four libraries ship in both uncompressed and compressed formats • YUI uses miniﬁcation: whitespace and comments are stripped • The Dojo build system uses “ShrinkSafe”, which compresses JavaScript using the Rhino parser • jQuery uses Dean Edwards’ Packer, with base62 encoding

Hosting on a CDN http://yui.yahooapis.com/2.2.2/build/reset/reset-min.css http://yui.yahooapis.com/2.2.2/build/dom/dom-min.js ... http://o.aolcdn.com/iamalpha/.resource/jssdk/dojo-0.4.1/dojo.js • JavaScript is cached before the user even visits your site

The law of leaky abstractions

You need to understand what your library is doing for you

Thank you

http://www.flickr.com/photos/klara/94704029/ http://www.flickr.com/photos/petele/407151800/ http://www.flickr.com/photos/adactio/464449077/ http://www.flickr.com/photos/thepartycow/62830567/ http://www.flickr.com/photos/lunchtimemama/97685471/

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JavaScript Libraries: The Big Picture

by Simon Willison

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