jQuery Anti-Patterns for Performance & Compression

jQuery Anti-Patterns for Performance & Compression Paul Irish NC JavaScript Camp ’10

Me. Interaction Designer at Molecular, Inc. jQuery Team Member - Dev. Relations @paul_irish http://paulirish.com Front-end development blog http://aurgasm.us Eclectic music blog

Performance

wassup shawty? how u doin’ Taskspeed Test Lines of Code 200 150 100 50 0 YUI Dojo 1.3.1 Dojo 1.2.3 Qooxdoo MooTools Prototype.js jQuery PureDOM

Oft cited best practices Cache length during loops Cache your selections Leverage documentFragment Append new content outside the loop

Oft cited best practices Cache length during loops // appending inside. bad. $.each(reallyLongArray, function(count, item) { Cache your selections var newLI = '<li>' + item + '</li>'; $('#ballers').append(newLI); Leverage documentFragment }); Append new content outside the loop // documentFragment off-DOM var frag = document.createDocumentFragment(); $.each(reallyLongArray, function(count, item) { var newLI = '<li>' + item + '</li>'; frag.appendChild(newLI[0]); }); $('#ballers')[0].appendChild(frag);

var newLI = '<li>' + item + '</li>'; $('#ballers').append(newLI); Oft cited best practices }); // documentFragment off-DOM var frag = document.createDocumentFragment(); Cache length during loops $.each(reallyLongArray, function(count, item) { var newLI = '<li>' + item + '</li>'; Cache your selections frag.appendChild(newLI[0]); }); Leverage documentFragment $('#ballers')[0].appendChild(frag); Append new content outside the loop // string concatenate and set innerHTML var myhtml = ''; $.each(reallyLongArray, function(count, item) { myhtml += '<li>' + item + '</li>'; }); $('#ballers').html(myhtml);

Keep things DRY If you’re repeating yourself, you’re doing it wrong

Moar DRY plz? if ($ventfade.data('currently') != 'showing') { $ventfade.stop(); } if ($venthover.data('currently') != 'showing') { $venthover.stop(); } if ($spans.data('currently') != 'showing') { $spans.stop(); } from http://mt-ventures.com/_js/global.js

All clean! Thx var elems = [$ventfade,$venthover,$spans]; $.each(elems,function(k,v){ if (v.data('currently') != 'showing'){ v.stop(); } })

Architecture Anti-Patterns Anonymous functions bound everywhere suck $(document).ready(function(){ ... $('#magic').click(function(e){ $('#yayeffects').slideUp(function(){ ... }); }); $('#happiness').load(url+' #unicorns',function(){ ... }) });

Architecture - Object Literal var PI = { onReady : function(){ ... $('#magic').click(PI.candyMtn); $('#happiness').load(url+' #unicorns',PI.unicornCb); }, candyMtn : function(e){ $('#yayeffects').slideUp(PI.slideCb); }, slideCb : function(){ ... }, unicornCb : function(){ ... } } $(document).ready(PI.onReady);

Architecture - Object Literal Advantages: Easier to navigate and discuss Proﬁlers give you actual names to work with You can execute these from ﬁrebug console You can write unit tests against them

Anti-Pattern: The requery // create and append your element $(document.body).append("<div class='baaron'/>"); // requery to bind stuff $("div.baaron").click(function(){}); // better: // swap to appendTo to hold your elem $("<div class='baaron'/>") .appendTo(document.body) .click(function(){});

$(‘#whats .the’,context)

This is not the .context property // find all stylesheets in the body var bodySheets = $('style',document.body); bodySheets.context // ==> BODY element Ignore that for the moment, I know no one that’s found a use

$(‘#whats .the’,context) Never pass it a selector string. Ever. No performance gain vs $(root).ﬁnd(selector) var arms = $('div.robotarm', '#container'); // instead do: var arms = $('#container').find('div.robotarm');

$(‘#whats .the’,context) You typically pass it this, but it’s purely a convenience to avoid ﬁnd() $('form.comments',this).submit(captureSubmit); // exact same as $(this).find('form.comments').submit(captureSubmit); Which is more readable? $('.reply_form', $(this).closest('.comment')).hide(); $(this).closest('.comment').find('.reply_form').hide();

The Crowd Say Bo Selector

Come on, my selector Selector engines have come a long, long way.

Come on, my selector Engines work in different ways Top-down, bottom-up, function creation, other crazy shit // from NWMatcher: // selecting '.outmost #outer span' T=e.nodeName;if(T=="SPAN"||T=="span") {while((e=e.parentNode)&&e.nodeType==1) {if((n=e.getAttributeNode("id"))&&n.value=="outer") {if((e=e.parentNode)&&e.nodeType==1) {C=e.className;if(C&&(" "+C+" ").indexOf(" outmost ")>-1) {r[X++]=N;continue main;}}}}}

Selector engines, parse direction Left to right (Top-down) Right to left (Bottom-up) Mootools Sizzle Sly YUI 3 Peppy NWMatcher Dojo Acme Ext JS Prototype.js details: http://alexsexton.com/selectors/

Selector engines, parse direction div.data table.attendees .gonzalez Left to right (Top-down) Right to left (Bottom-up) Mootools Sizzle Sly YUI 3 Peppy NWMatcher Dojo Acme Ext JS Prototype.js details: http://alexsexton.com/selectors/

Selector engines, parse direction Left to right (Top-down) Right to left (Bottom-up) Mootools Sizzle Sly YUI 3 Peppy NWMatcher Dojo Acme Ext JS Prototype.js details: http://alexsexton.com/selectors/

Selector engines, parse direction Left to right (Top-down) Right to left (Bottom-up) Mootools Sizzle Sly YUI 3 Peppy NWMatcher Dojo Acme querySelectorAll (qSA) Ext JS Prototype.js details: http://alexsexton.com/selectors/

Selector Optimization Speciﬁc on the right, light on the left // let's find scott div.data .gonzalez // specific on right, light on the left .data td.gonzalez tag.class if possible on your right-most selector. just tag or just .class on left.

Selector Optimization Of course, descending from an #id is best // basic #id-based selector var arms = $('#container div.robotarm'); // hyper-optimized #id case first, then find: var arms = $('#container').find('div.robotarm');

Selector Optimization Don’t be needlessly specific // let's find scott .data table.attendees td.gonzalez // better: drop the middle .data td.gonzalez A flatter DOM helps, so move to HTML5 Also a wider range of tags speeds up filters

Selector Optimization Avoid the universal selector Avoid the implied universal selector $('.buttons > *') // terribly costly $('.buttons').children() // much better $('.gender :radio') // implied universal $('.gender *:radio') // exact same, explicit now $('.gender input:radio') // much better

Selector Optimization Google PageSpeed’s efficient selectors analysis MDC: Writing Efficient CSS https://developer.mozilla.org/en/Writing_Efficient_CSS Benchmark.js http://code.paulirish.com/sandbox/benchmark.js

Event Delegation function delegate(type, delegate, handler) { return $(document).bind(type, function(event) { var target = $(event.target); if (target.is(delegate)) { return handler.apply(target, arguments); } }); } delegate('click','td.jehl',createRockstar); // and with live(): $('td.jehl').live('click',createRockstar);

Event Delegation live() isn’t just for dynamic content Speeds up page load Only one event handler is bound vs many Good for >3 elements all getting the same handler // using live(), skipping selection on load var jqElem = $(document); jqElem.selector = 'li.ui'; jqElem.live('dblclick', dblhandler);

Event Delegation delegate() bakes in huge performance gains explicit context reduces overhead by ~80% Use it instead of live() if possible // awkward but equivalent $('a.trigger',$('#container')[0]).live('click',handlerFn) // so damn fine $('#container').delegate('click','a.trigger',handlerFn)

Event Delegation new in 1.4 .2! delegate() bakes in huge performance gains explicit context reduces overhead by ~80% Use it instead of live() if possible // awkward but equivalent $('a.trigger',$('#container')[0]).live('click',handlerFn) // so damn fine $('#container').delegate('click','a.trigger',handlerFn)

The DOM is slow Pull elements off the DOM while you toy with them var table = $('#some-table'); var parent = table.parent(); table.detach(); table.addLotsAndLotsOfRows(); parent.append(table);

The DOM is slow Pull elements off the DOM while you toy with them var table = $('#some-table'); var parent = table.parent(); new table.detach(); in 1 .4 table.addLotsAndLotsOfRows(); parent.append(table);

Minimize DOM touches Use classes, but if a style change user-selected: jQuery('a.swedberg').css('color', '#BADA55'); jQuery('<style type="text/css"> a.swedberg { color: BADA55; } </style>') .appendTo('head'); Timings for X elements 3000 2250 (1000 iterations) 1500 css() style tag 750 0 1 5 10 20 50

Minimize DOM touches

Don’t treat jQuery as a Black Box Use the source as your documentation Add this to your bookmark bar, NOW! http://ajax.googleapis.com/ajax/libs/jquery/1/jquery.js http://bit.ly/jqsource Determine which are convenience methods: getScript: function( url, callback ) { return jQuery.get(url, null, callback, "script"); }, getJSON: function( url, data, callback ) { return jQuery.get(url, data, callback, "json"); },

Don’t treat jQuery as a Black Box Learn the lesser-known methods map(), slice(), stop(), (de)queue(), prevAll(), pushStack(), inArray() , etc // index() in jQuery <= 1.3.2 $('#rdworth').parent().children().index( $('#rdworth')[0] ) // using prevAll() is 10% faster (also sexier) $('#rdworth').prevAll().length // in jQuery 1.4 $('#rdworth').index()

Don’t act on absent elements jQuery is very kind and doesn’t throw errors at you Don’t assume it’s just ﬁne to do $('#doesntexist').slideUp() // this will execute genFx(), speed() and animate() // before it hits an each() jQuery UI widgets have a lot of overhead you’ll hit

Don’t act on absent elements jQuery.fn.doOnce = function(func){ this.length && func.apply(this); return this; } $('li.cartitems').doOnce(function(){ // make it ajax! o/ });

Don’t act on absent elements $.fn.plugin = function(opts){ if(!this.length) return this; var opts = $.extend(...... ... return this.each(...

Setter Methods view-source:setters.js

new New Element Creation 1.4 ! in jQuery("<div/>", { id: "foo", rel : "something" css: { height: "50px", width: "50px", color: "blue", backgroundColor: "#ccc" }, click: function() { $(this).css("backgroundColor", "red"); } }).appendTo("body");

new eq(), ﬁrst(), last() 1.4 ! in var lastelem = $elems.eq(-1); // get() too! $('#nav li:first') === $('#nav li').first() $('#nav li:last') === $('#nav li').last()

Data() // regular: $(elem).data(key,value); // omg like 10x faster: $.data(elem,key,value);

Compression

Compression YUI Compressor Sits on Rhino. Comments, whitespace, variable replacement //it already does these micro-optimizations: object['prop'] ==> object.prop {'key':123} ==> {key:123} 'jon's apostophes' ==> "jon's apostrophes" 'bigass ' + 'string' ==> 'bigass string'

Variable deﬁnition // old 'n busted // new hotness var test1 = 1; var test1 = 1, var test2 = function() { test2 = function() { // function code // function code }; }, var test3 = test2(test1); test3 = test2(test1);

Munge the primitives Deﬁne shortcuts at the top of your scope Good for both compression and scope chain traversal var TRUE = true, FALSE = false, NULL = null, window = self, undefined = undefined;

Munge the primitives Deﬁne shortcuts at the top of your scope Good for both compression and scope chain traversal var TRUE = true, FALSE = false, NULL = null, window = self, undefined; undefined = undefined;

Munge the primitives (function(){ var window = this, document = document, undefined; /* code */ })(); (function(window, document, undefined){ /* code */ })(this,this.document);

var str=‘Let’s put this into action’ // html.no-js html> <!doctype ==> html.js var elem = document.getElementsByTagName('html')[0]; elem.className = elem.className.replace('no-js','js'); <html class="no-js"> // quicker reference, safer replace <head> var elem = document.documentElement; elem.className = elem.className.replace(/bno-jsb/,'js'); <script> // one// change the html class to 'js' line ftw! // in the head, no FOUC document.documentElement.className = document.documentElement.className.replace(/bno-jsb/, </script> 'js'); </body> // shorter with a self-executing anonymous function (function(B){B.className=B.className.replace(/bno-jsb/,

var str=‘Let’s put this into action’ // html.no-js ==> html.js var elem = document.getElementsByTagName('html')[0]; elem.className = elem.className.replace('no-js','js'); // quicker reference, safer replace var elem = document.documentElement; elem.className = elem.className.replace(/bno-jsb/,'js'); // one line ftw! document.documentElement.className = document.documentElement.className.replace(/bno-jsb/, 'js'); // shorter with a self-executing anonymous function (function(B){B.className=B.className.replace(/bno-jsb/,

// html.no-js ==> html.js var elem = document.getElementsByTagName('html')[0]; var str=‘Let’s put this into action’ elem.className = elem.className.replace('no-js','js'); // quicker reference, safer replace var elem = document.documentElement; elem.className = elem.className.replace(/bno-jsb/,'js'); // one line ftw! document.documentElement.className = document.documentElement.className.replace(/bno-jsb/, 'js'); // shorter with a self-executing anonymous function (function(B){B.className=B.className.replace(/bno-jsb/, 'js')})(document.documentElement); // pass className, object string notation (function(H,C){H[C]=H[C].replace(/bno-jsb/,'js')}) (document.documentElement,'className')

Conditionals // old 'n busted if ( type === 'foo' || type === 'bar' ) {} // regex test if ( /^(foo|bar)$/.test(type) ) {} // obj literal lookup (smaller if <5 items) if ( ({foo:1,bar:1})[type] ) {}

Logic and Ternary operands // basic function detection document.querySelectorAll && document.querySelectorAll('a:nth-child(2)') // assignment is legal, but it evaluates to the right expression callback && (isCallbackCalled = true) && callback(returnVal); // call or cache the callback function (isCallbackCalled || returnVal) ? fn(returnVal) : (callback = fn); // inline function calls isToday('Saturday') && Math.round(Math.random()) && $('#winnar').show() // if JSON2.js or Native JSON is present, otherwise eval. data = window.JSON && JSON.parse(data) || eval('('+data +')');

Write maintainable code As a developer, you should work ﬁrst and foremost for the user of your products. The second most important person to work for is the developer that takes over from you. - Christian Heilmann

Comments /*! * Will not be removed by YUI Compressor */ // for quick toggling on and off: /* */ aaaahYeah(); /* */ /* * / ohHellNo(); /* */

Compression Tools CompressorRater http://compressorrater.thruhere.net/ YUI Compressor front-end http://refresh-sf.com/yui/

Thanks, ya’ll. Slides at http://paulirish.com/perf @paul_irish thx: Alex Sexton, Ben Alman, Adam Sontag, James Padolsey, temp01, #jquery on Freenode

todo shadow effect to code samples more context research and this: http:// groups.google.com/group/jquery-dev/msg/ b4b7935a4013dfe7 and http://ispeakwebstuff.co.uk/ web-design-development-tutorials/clever-jquery- selectors/

` // pngfix for IE6 // e.g. FL.pngfix('img.bigProdShot,a.thumb'); pngfix : function(sel){ // conditional comments for inclusion of that js. if (typeof DD_belatedPNG == 'undefined'){ return; } else { // delay pngfix until window onload $(window).load(function(){ $(sel).each(function() { DD_belatedPNG.fixPng(arguments[1]); }); }); } } // end of FL.pngfix()

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jQuery Anti-Patterns for Performance & Compression

by Paul Irish on Sep 11, 2009

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