Steve Souders Even Faster Web Sites Disclaimer: This content does not necessarily reflect the opinions of my employer.

17% 83% iGoogle, primed cache the importance of frontend performance 9%91% iGoogle, empty cache

time spent on the frontend Empty CachePrimed Cache search.live.com/results67%0% en.wikipedia.org/wiki94%91% April 2008

The Performance Golden Rule 80-90% of the end-user response time is spent on the frontend. Start there. greater potential for improvement simpler proven to work

14 R ULES 1.M AKE FEWER HTTP REQUESTS 2.U SE A CDN 3.A DD AN E XPIRES HEADER 4.G ZIP COMPONENTS 5.P UT STYLESHEETS AT THE TOP 6.P UT SCRIPTS AT THE BOTTOM 7.A VOID CSS EXPRESSIONS 8.M AKE JS AND CSS EXTERNAL 9.R EDUCE DNS LOOKUPS 10.M INIFY JS 11.A VOID REDIRECTS 12.R EMOVE DUPLICATE SCRIPTS 13.C ONFIGURE ET AGS 14.M AKE AJAX CACHEABLE

Sept 2007

June 2009

Even Faster Web Sites Splitting the initial payload Loading scripts without blocking Coupling asynchronous scripts Positioning inline scripts Sharding dominant domains Flushing the document early Using iframes sparingly Simplifying CSS Selectors Understanding Ajax performance Doug Crockford Creating responsive web apps Ben Galbraith, Dion Almaer Writing efficient JavaScript Nicholas Zakas Scaling with Comet Dylan Schiemann Going beyond gzipping Tony Gentilcore Optimizing images Stoyan Stefanov, Nicole Sullivan

AOL eBay Facebook MySpace Wikipedia Yahoo! Why focus on JavaScript? YouTube

scripts block blocks parallel downloads and rendering 7 secs: IE 8, FF 3.5(?), Chr 2, Saf 4 What's Cuzillion? 9 secs: IE 6-7, FF 3.0, Chr 1, Op 9-10, Saf 3

a tool for quickly constructing web pages to see how components interact Open Source Cuzillion 'cuz there are a zillion pages to check

JavaScript Functions Executed before onload % search.live.com/results17K24% en.wikipedia.org/wiki114K32% % avg 252K avg initial payload and execution

Splitting the initial payload split your JavaScript between what's needed to render the page and everything else load "everything else" after the page is rendered separate manually (Firebug); tools needed to automate this (Doloto from Microsoft) load scripts without blocking – how?

MSN Scripts and other resources downloaded in parallel! How? Secret sauce?! var p= g.getElementsByTagName("HEAD")[0]; var c=g.createElement("script"); c.type="text/javascript"; c.onreadystatechange=n; c.onerror=c.onload=k; c.src=e; p.appendChild(c) MSN.com: parallel scripts

Loading Scripts Without Blocking XHR Eval XHR Injection Script in Iframe Script DOM Element Script Defer document.write Script Tag

XHR Eval script must have same domain as main page must refactor script var xhrObj = getXHRObject(); xhrObj.onreadystatechange = function() { if ( xhrObj.readyState != 4 ) return; eval(xhrObj.responseText); }; xhrObj.open('GET', 'A.js', true); xhrObj.send('');

XHR Injection var xhrObj = getXHRObject(); xhrObj.onreadystatechange = function() { if ( xhrObj.readyState != 4 ) return; var se=document.createElement('script'); document.getElementsByTagName('head') [0].appendChild(se); se.text = xhrObj.responseText; }; xhrObj.open('GET', 'A.js', true); xhrObj.send(''); script must have same domain as main page

Script in Iframe <iframe src='A.html' width=0 height=0 frameborder=0 id=frame1> iframe must have same domain as main page must refactor script: // access iframe from main page window.frames[0].createNewDiv(); // access main page from iframe parent.document.createElement('div');

Script DOM Element var se = document.createElement('script'); se.src = ' document.getElementsByTagName('head') [0].appendChild(se); script and main page domains can differ no need to refactor JavaScript

Script Defer only supported in IE (just landed in FF 3.1) script and main page domains can differ no need to refactor JavaScript

document.write Script Tag document.write(" "); parallelization only works in IE parallel downloads for scripts, nothing else all document.write s must be in same script block

browser busy indicators

status bar progress bar logocursor block render block onload normal Script Src FFIE,FF FFIE,FF XHR Eval no XHR Injection no Script in Iframe IE,FFFFIE,FFFFnoIE,FF Script DOM Element FF noFF Script Defer FF IE,FF document.write Script Tag FFIE,FF FFIE,FF good to show busy indicators when the user needs feedback bad when downloading in the background

Ensure scripts execute in order: necessary when scripts have dependencies IE: FF: Avoid scripts executing in order: faster – first script back is executed immediately ensure/avoid ordered execution

Loading Scripts Without Blocking || down- loads domains can differ existing scripts browser busy ensures order size (bytes) normal Script Src noyes IE,FF ~50 XHR Eval IE,FFno ~500 XHR Injection IE,FFnoyesno ~500 Script in Iframe IE,FFno IE,FFno~50 Script DOM Element IE,FFyes FF ~200 Script Defer IEyes IE,FFIE~50 document.write Script Tag IE * yes IE,FFIE~100 * Only other document.write scripts are downloaded in parallel (in the same script block).

and the winner is... XHR Eval XHR Injection Script in iframe Script DOM Element Script Defer Script DOM Element Script Defer Script DOM Element Script DOM Element (FF) Script Defer (IE) XHR Eval XHR Injection Script in iframe Script DOM Element (IE) XHR Injection XHR Eval Script DOM Element (IE) Managed XHR Injection Managed XHR Eval Script DOM Element Managed XHR Injection Managed XHR Eval Script DOM Element (FF) Script Defer (IE) Managed XHR Eval Managed XHR Injection Script DOM Element (FF) Script Defer (IE) Managed XHR Eval Managed XHR Injection different domains same domains no order preserve orderno order no busy show busy no busy preserve order

Loading Scripts Without Blocking don't let scripts block other downloads you can still control execution order, busy indicators, and onload event What about inline scripts?

synchronous JS example: menu.js var aExamples = [ ['couple-normal.php', 'Normal Script Src'], ['couple-xhr-eval.php', 'XHR Eval'],... ['managed-xhr.php', 'Managed XHR'] ]; function init() { EFWS.Menu.createMenu('examplesbtn', aExamples); } init();

asynchronous JS example: menu.js var domscript = document.createElement('script'); domscript.src = "menu.js"; document.getElementsByTagName('head')[0].appendChild(domscri pt); var aExamples = [ ['couple-normal.php', 'Normal Script Src'], ['couple-xhr-eval.php', 'XHR Eval'],... ['managed-xhr.php', 'Managed XHR'] ]; function init() { EFWS.Menu.createMenu('examplesbtn', aExamples); } init(); script DOM element approach

before after

Loading Scripts Without Blocking || down- loads domains can differ existing scripts browser busy ensures order size (bytes) normal Script Src noyes IE,FF ~50 XHR Eval IE,FFno ~500 XHR Injection IE,FFnoyesno ~500 Script in Iframe IE,FFno IE,FFno~50 Script DOM Element IE,FFyes FF ~200 Script Defer IEyes IE,FFIE~50 document.write Script Tag IE * yes IE,FFIE~100 * Only other document.write scripts are downloaded in parallel (in the same script block). !IE

what about inlined code that depends on the script?

baseline coupling results (not good) Preserve Execution Order Load Script & Image in Parallel normal Script Src allIE8, Saf4, Chr2 XHR Eval -all XHR Injection -all Script in Iframe -all Script DOM Element FF, OpIE, FF, Saf, Chr Script Defer FF, Saf, Chr, OpIE, (Saf4, Chr2) * document.write Script Tag allSaf4, Chr2 * Scripts download in parallel regardless of the Defer attribute. need a way to load scripts asynchronously AND preserve order

coupling techniques hardcoded callback window onload timer degrading script tags script onload

technique 1: hardcoded callback var aExamples = [['couple-normal.php', 'Normal Script Src'],...]; function init() { EFWS.Menu.createMenu('examplesbtn', aExamples); } var domscript = document.createElement('script'); domscript.src = "menu.js"; document.getElementsByTagName('head')[0].appendChild(domscri pt); init() is called from within menu.js not very flexible doesn't work for 3 rd party scripts

technique 2: window onload var aExamples = [['couple-normal.php', 'Normal Script Src'],...]; function init() { EFWS.Menu.createMenu('examplesbtn', aExamples); } if ( window.addEventListener ) { window.addEventListener("load", init, false); } else if ( window.attachEvent ) { window.attachEvent("onload", init); } init() is called at window onload must use async technique that blocks onload: Script in Iframe does this across most browsers init() called later than necessary

technique 3: timer var domscript = document.createElement('script'); domscript.src = "menu.js"; document.getElementsByTagName('head')[0].appendChild(domscript); var aExamples = [['couple-normal.php', 'Normal Script Src'],...]; function init() { EFWS.Menu.createMenu('examplesbtn', aExamples); } function initTimer(interval) { if ( "undefined" === typeof(EFWS) ) { setTimeout(initTimer, interval); } else { init(); } initTimer(300); load if interval too low, delay if too high slight increased maintenance – EFWS

John Resig's degrading script tags var aExamples = [['couple-normal.php', 'Normal Script Src'],...]; function init() { EFWS.Menu.createMenu('examplesbtn', aExamples); } init(); at the end of menu-degrading.js: var scripts = document.getElementsByTagName("script"); var cntr = scripts.length; while ( cntr ) { var curScript = scripts[cntr-1]; if (curScript.src.indexOf("menu-degrading.js") != -1) { eval( curScript.innerHTML ); break; } cntr--; } cleaner clearer safer – inlined code not called if script fails no browser supports it

technique 4: degrading script tags var aExamples = [['couple-normal.php', 'Normal Script Src'],...]; function init() { EFWS.Menu.createMenu('examplesbtn', aExamples); } var domscript = document.createElement('script'); domscript.src = "menu-degrading.js"; if ( -1 != navigator.userAgent.indexOf("Opera") ) { domscript.innerHTML = "init();"; } else { domscript.text = "init();"; } document.getElementsByTagName('head')[0].appendChild(domscript); elegant, flexible (cool!) not well known doesn't work for 3 rd party scripts (unless...)

technique 5: script onload var aExamples = [['couple-normal.php', 'Normal Script Src'],...]; function init() { EFWS.Menu.createMenu('examplesbtn', aExamples); } var domscript = document.createElement('script'); domscript.src = "menu.js"; domscript.onloadDone = false; domscript.onload = function() { if ( ! domscript.onloadDone ) { init(); } domscript.onloadDone = true; }; domscript.onreadystatechange = function() { if ( "loaded" === domscript.readyState ) { if ( ! domscript.onloadDone ) { init(); } domscript.onloadDone = true; } document.getElementsByTagName('head')[0].appendChild(domscript); pretty nice, medium complexity

what about multiple scripts that depend on each other, and inlined code that depends on the scripts? two solutions: Managed XHR DOM Element and Doc Write

multiple script example: menutier.js var aRaceConditions = [['couple-normal.php', 'Normal...]; var aWorkarounds = [['hardcoded-callback.php', 'Hardcod...]; var aMultipleScripts = [['managed-xhr.php', 'Managed XH...]; var aLoadScripts = [['loadscript.php', 'loadScript'],...]; var aSubmenus = [["Race Conditions", aRaceConditions], ["Workarounds", aWorkarounds], ["Multiple Scripts", aMultipleScripts], ["General Solution", aLoadScripts]]; function init() { EFWS.Menu.createTieredMenu('examplesbtn', aSubmenus); }

technique 1: managed XHR var aRaceConditions = [['couple-normal.php', 'Normal...]; var aWorkarounds = [['hardcoded-callback.php', 'Hardcod...]; var aMultipleScripts = [['managed-xhr.php', 'Managed XH...]; var aLoadScripts = [['loadscript.php', 'loadScript'],...]; var aSubmenus = [["Race Conditions", aRaceConditions],...]; function init() { EFWS.Menu.createTieredMenu('examplesbtn', aSubmenus); } EFWS.Script.loadScriptXhrInjection("menu.js", null, true); EFWS.Script.loadScriptXhrInjection("menutier.js", init, true); XHR Injection asynchronous technique does not preserve order – we have to add that before after

EFWS.loadScriptXhrInjection // Load an external script. // Optionally call a callback and preserve order. loadScriptXhrInjection: function(url, onload, bOrder) { var iQ = EFWS.Script.queuedScripts.length; if ( bOrder ) { var qScript = { response: null, onload: onload, done: false }; EFWS.Script.queuedScripts[iQ] = qScript; } var xhrObj = EFWS.Script.getXHRObject(); xhrObj.onreadystatechange = function() { if ( xhrObj.readyState == 4 ) { if ( bOrder ) { EFWS.Script.queuedScripts[iQ].response = xhrObj.responseText; EFWS.Script.injectScripts(); } else { eval(xhrObj.responseText); if ( onload ) { onload(); } }; xhrObj.open('GET', url, true); xhrObj.send(''); } process queue (next slide)or... eval now, call callback save response to queue add to queue (if bOrder)

EFWS.injectScripts // Process queued scripts to see if any are ready to inject. injectScripts: function() { var len = EFWS.Script.queuedScripts.length; for ( var i = 0; i < len; i++ ) { var qScript = EFWS.Script.queuedScripts[i]; if ( ! qScript.done ) { if ( ! qScript.response ) { // STOP! need to wait for this response break; } else { eval(qScript.response); if ( qScript.onload ) { qScript.onload(); } qScript.done = true; } ready for this script, eval and call callback bail – need to wait to preserve order if not yet injected preserves external script ordernon-blocking works in all browserscouples with inlined code works with scripts across domains

technique 2: DOM Element and Doc Write Preserve Execution Order Load Scripts in Parallel Load Script & Image in Parallel Script DOM Element FF, Op FF, Op, IE, Saf, Chr FF, IE, Saf, Chr Script Defer IE, Saf, Chr, FF, Op IE document.write Script Tag IE, Saf, Chr, FF, Op IE, Op Firefox & Opera – use Script DOM Element IE – use document.write Script Tag Safari, Chrome – no benefit; rely on Safari 4 and Chrome 2

EFWS.loadScripts loadScripts: function(aUrls, onload) { // first pass: see if any of the scripts are on a different domain var nUrls = aUrls.length; var bDifferent = false; for ( var i = 0; i < nUrls; i++ ) { if ( EFWS.Script.differentDomain(aUrls[i]) ) { bDifferent = true; break; } // pick the best loading function var loadFunc = EFWS.Script.loadScriptXhrInjection; if ( bDifferent ) { if ( -1 != navigator.userAgent.indexOf('Firefox') || -1 != navigator.userAgent.indexOf('Opera') ) { loadFunc = EFWS.Script.loadScriptDomElement; } else { loadFunc = EFWS.Script.loadScriptDocWrite; } // second pass: load the scripts for ( var i = 0; i < nUrls; i++ ) { loadFunc(aUrls[i], ( i+1 == nUrls ? onload : null ), true); }

multiple scripts with dependencies var aRaceConditions = [['couple-normal.php', 'Normal...]; var aWorkarounds = [['hardcoded-callback.php', 'Hardcod...]; var aMultipleScripts = [['managed-xhr.php', 'Managed XH...]; var aLoadScripts = [['loadscript.php', 'loadScript'],...]; var aSubmenus = [["Race Conditions", aRaceConditions],...]; function init() { EFWS.Menu.createTieredMenu('examplesbtn', aSubmenus); } EFWS.Script.loadScripts(["menu.js", "menutier.js"], init); scripts on same domain: order preserved, no blocking scripts on different domain: order preserved: all loads scripts in parallel: all except Saf3, Chr1 load script and image in parallel: FF, Saf4, Chr2

asynchronous scripts wrap-up Technique Preserve Order Load Scripts in Parallel Load Script & Image in Parallel single script Script DOM Element na all multiple scripts, no dependencies Script DOM Element naall multiple scripts, dependencies, same domain Managed XHRall multiple scripts, dependencies, same domain Script DOM Element (FF, Op), Doc Write (IE, Saf, Chr) all !Saf3, !Chr1 FF, Saf4, Chr2

case study: Google Analytics recommended pattern: 1 var gaJsHost = ((" == document.location.protocol) ? " : " document.write(unescape("%3Cscript src='" + gaJsHost + "google-analytics.com/ga.js' type='text/javascript'%3E%3C/script%3E")); var pageTracker = _gat._getTracker("UA-xxxxxx-x"); pageTracker._trackPageview(); document.write Script Tag approach blocks other resources 1

case study: dojox.analytics.Urchin 1 _loadGA: function(){ var gaHost = (" == document.location.protocol) ? " : " dojo.create('script', { src: gaHost + "google-analytics.com/ga.js" }, dojo.doc.getElementsByTagName("head")[0]); setTimeout(dojo.hitch(this, "_checkGA"), this.loadInterval); }, _checkGA: function(){ setTimeout(dojo.hitch(this, !window["_gat"] ? "_checkGA" : "_gotGA"), this.loadInterval); }, _gotGA: function(){ this.tracker = _gat._getTracker(this.acct);... } Script DOM Element approach "timer" coupling technique (script onload better) 1

asynchronous loading & coupling async technique: Script DOM Element easy, cross-browser doesn't ensure script order coupling technique: script onload fairly easy, cross-browser ensures execution order for external script and inlined code multiple interdependent external and inline scripts: much more complex (see hidden slides) concatenate your external scripts into one!

bad: stylesheet followed by inline script browsers download stylesheets in parallel with other resources that follow......unless the stylesheet is followed by an inline script best to move inline scripts above stylesheets or below other resources use Link,

eBay MSN MySpace Wikipedia mispositioned inline scripts

Positioning Inline Scripts remember inline scripts carry a cost avoid long-executing inline scripts don't put inline scripts between stylesheets and other resources

flushing the document early gotchas: PHP output_buffering – ob_flush() Transfer-Encoding: chunked gzip – Apache's DeflateBufferSize before proxies and anti-virus software browsers – Safari (1K), Chrome (2K) other languages: $| or FileHandle autoflush (Perl), flush (Python), ios.flush (Ruby) html image script html image script call PHP's flush()

flushing and domain blocking you might need to move flushed resources to a domain different from the HTML doc html image script html image script google image script image 204 case study: Google search blocked by HTML document different domains

KW=sony&CLT=SCH Nike_Mens_Super_Bad_Ft_Football_Cleats

slow spots: top – shard CSS and JS, flush middle – shard images bottom – scripts (async?) use CSS sprites (42 bg images) add future Expires header optimize images (50K, 20%) remove ETags

?KW=sony&CLT=SCH slow spots: HTML document – flush bottom – ads (async?, onload?) use CSS sprites (42 bg images) add future Expires header optimize images (20K, 15%) remove ETags

Nike_Mens_Super_Bad_Ft_Football _Cleats slow spots: HTML document – flush top – shard CSS and JS, move CSS above JS move inline JS above stylesheet use CSS sprites (42 bg images) add future Expires header optimize images (50K, 11%) remove unused CSS (27K, 20%) remove ETags

takeaways focus on the frontend run YSlow: speed matters

impact on revenue Google: Yahoo: Amazon: ms -20% traffic ms -5-9% full-page traffic ms -1% sales 1

cost savings hardware – reduced load bandwidth – reduced response size

if you want better user experience more revenue reduced operating expenses the strategy is clear Even Faster Web Sites

Steve Souders