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Google在Web前端方面的经验
Google在Web前端方面的经验
Google在Web前端方面的经验
Google在Web前端方面的经验
Google在Web前端方面的经验
Google在Web前端方面的经验
Google在Web前端方面的经验
Google在Web前端方面的经验
Google在Web前端方面的经验
Google在Web前端方面的经验
Google在Web前端方面的经验
Google在Web前端方面的经验
Google在Web前端方面的经验
Google在Web前端方面的经验
Google在Web前端方面的经验
Google在Web前端方面的经验
Google在Web前端方面的经验
Google在Web前端方面的经验
Google在Web前端方面的经验
Google在Web前端方面的经验
Google在Web前端方面的经验
Google在Web前端方面的经验
Google在Web前端方面的经验
Google在Web前端方面的经验
Google在Web前端方面的经验
Google在Web前端方面的经验
Google在Web前端方面的经验
Google在Web前端方面的经验
Google在Web前端方面的经验
Google在Web前端方面的经验
Google在Web前端方面的经验
Google在Web前端方面的经验
Google在Web前端方面的经验
Google在Web前端方面的经验
Google在Web前端方面的经验
Google在Web前端方面的经验
Google在Web前端方面的经验
Google在Web前端方面的经验
Google在Web前端方面的经验
Google在Web前端方面的经验
Google在Web前端方面的经验
Google在Web前端方面的经验
Google在Web前端方面的经验
Google在Web前端方面的经验
Google在Web前端方面的经验
Google在Web前端方面的经验
Google在Web前端方面的经验
Google在Web前端方面的经验
Google在Web前端方面的经验
Google在Web前端方面的经验
Google在Web前端方面的经验
Google在Web前端方面的经验
Google在Web前端方面的经验
Google在Web前端方面的经验
Google在Web前端方面的经验
Google在Web前端方面的经验
Google在Web前端方面的经验
Google在Web前端方面的经验
Google在Web前端方面的经验
Google在Web前端方面的经验
Google在Web前端方面的经验
Google在Web前端方面的经验
Google在Web前端方面的经验
Google在Web前端方面的经验
Google在Web前端方面的经验
Google在Web前端方面的经验
Google在Web前端方面的经验
Google在Web前端方面的经验
Google在Web前端方面的经验
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Google在Web前端方面的经验

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  1. Steve Souders [email_address] http://stevesouders.com/docs/sxsw-20090314.ppt Even Faster Web Sites Disclaimer: This content does not necessarily reflect the opinions of my employer.
  2. the importance of frontend performance 17% 83% iGoogle, primed cache 9% 91% iGoogle, empty cache
  3. time spent on the frontend April 2008 Empty Cache Primed Cache www.aol.com 97% 97% www.ebay.com 95% 81% www.facebook.com 95% 81% www.google.com/search 47% 0% search.live.com/results 67% 0% www.msn.com 98% 94% www.myspace.com 98% 98% en.wikipedia.org/wiki 94% 91% www.yahoo.com 97% 96% www.youtube.com 98% 97%
  4. 14 RULES <ul><li>MAKE FEWER HTTP REQUESTS </li></ul><ul><li>USE A CDN </li></ul><ul><li>ADD AN EXPIRES HEADER </li></ul><ul><li>GZIP COMPONENTS </li></ul><ul><li>PUT STYLESHEETS AT THE TOP </li></ul><ul><li>PUT SCRIPTS AT THE BOTTOM </li></ul><ul><li>AVOID CSS EXPRESSIONS </li></ul><ul><li>MAKE JS AND CSS EXTERNAL </li></ul><ul><li>REDUCE DNS LOOKUPS </li></ul><ul><li>MINIFY JS </li></ul><ul><li>AVOID REDIRECTS </li></ul><ul><li>REMOVE DUPLICATE SCRIPTS </li></ul><ul><li>CONFIGURE ETAGS </li></ul><ul><li>MAKE AJAX CACHEABLE </li></ul>
  5.  
  6.  
  7.  
  8. 25% discount code: &quot;ssouders25&quot;
  9. Sept 2007
  10. June 2009
  11. Even Faster Websites Split the initial payload Load scripts without blocking Couple asynchronous scripts Don't scatter inline scripts Split the dominant domain Flush the document early Use iframes sparingly Simplify CSS Selectors Ajax performance (Doug Crockford) Writing efficient JavaScript (Nicholas Zakas) Creating responsive web apps (Ben Galbraith, Dion Almaer) Comet (Dylan Schiemann) Beyond Gzipping (Tony Gentilcore) Optimize Images (Stoyan Stefanov, Nicole Sullivan)
  12. why focus on JavaScript? AOL eBay Facebook MySpace Wikipedia Yahoo! YouTube
  13. scripts block <script src=&quot;A.js&quot;> blocks parallel downloads and rendering http://stevesouders.com/cuzillion/?ex=10008
  14. MSN.com: parallel scripts Scripts and other resources downloaded in parallel! How? Secret sauce?! var p= g.getElementsByTagName(&quot;HEAD&quot;)[0]; var c=g.createElement(&quot;script&quot;); c.type=&quot;text/javascript&quot;; c.onreadystatechange=n; c.onerror=c.onload=k; c.src=e; p.appendChild(c) MSN
  15. asynchronous script loading XHR Eval XHR Injection Script in Iframe Script DOM Element Script Defer document.write Script Tag
  16. 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(''); http://stevesouders.com/cuzillion/?ex=10009
  17. 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 http://stevesouders.com/cuzillion/?ex=10015
  18. Script in Iframe <iframe src='A.html' width=0 height=0 frameborder=0 id=frame1></iframe> <ul><li>iframe must have same domain as main page </li></ul><ul><li>must refactor script: </li></ul><ul><ul><li>// access iframe from main page </li></ul></ul><ul><ul><li>window.frames[0].createNewDiv(); </li></ul></ul><ul><ul><li>// access main page from iframe </li></ul></ul><ul><ul><li>parent.document.createElement('div'); </li></ul></ul>http://stevesouders.com/cuzillion/?ex=10012
  19. Script DOM Element var se = document.createElement('script'); se.src = 'http://anydomain.com/A.js'; document.getElementsByTagName('head')[0] .appendChild(se); script and main page domains can differ no need to refactor JavaScript http://stevesouders.com/cuzillion/?ex=10010
  20. Script Defer <script defer src='A.js'></script> only supported in IE (just landed in FF 3.1) script and main page domains can differ no need to refactor JavaScript http://stevesouders.com/cuzillion/?ex=10013
  21. document.write Script Tag document.write (&quot;<scr&quot; + &quot;ipt type='text/javascript' src='A.js'>&quot; + &quot;</scr&quot; + &quot;ipt>&quot;); parallelization only works in IE parallel downloads for scripts, nothing else all document.write s must be in same script block http://stevesouders.com/cuzillion/?ex=10014
  22. browser busy indicators
  23. browser busy indicators good to show busy indicators when the user needs feedback bad when downloading in the background
  24. ensure/avoid ordered execution <ul><li>Ensure scripts execute in order: </li></ul><ul><ul><li>necessary when scripts have dependencies </li></ul></ul><ul><ul><li>IE: http://stevesouders.com/cuzillion/?ex=10017 </li></ul></ul><ul><ul><li>FF: http://stevesouders.com/cuzillion/?ex=10018 </li></ul></ul><ul><li>Avoid scripts executing in order: </li></ul><ul><ul><li>faster – first script back is executed immediately </li></ul></ul><ul><ul><li>http://stevesouders.com/cuzillion/?ex=10019 </li></ul></ul>
  25. load scripts without blocking * Only other document.write scripts are downloaded in parallel (in the same script block).
  26. 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 order no order no busy show busy show busy no busy preserve order
  27. load scripts without blocking <ul><li>don't let scripts block other downloads </li></ul><ul><li>you can still control execution order, busy indicators, and onload event </li></ul><ul><li>What about inline scripts? </li></ul>
  28.  
  29. synchronous JS example: menu.js <ul><li><script src=&quot;menu.js&quot; type=&quot;text/javascript&quot;></script> </li></ul><ul><li><script type=&quot;text/javascript&quot;> </li></ul><ul><li>var aExamples = </li></ul><ul><li>[ </li></ul><ul><li>['couple-normal.php', 'Normal Script Src'], </li></ul><ul><li>['couple-xhr-eval.php', 'XHR Eval'], </li></ul><ul><li>... </li></ul><ul><li>['managed-xhr.php', 'Managed XHR'] </li></ul><ul><li>]; </li></ul><ul><li>function init() { </li></ul><ul><li>EFWS.Menu.createMenu('examplesbtn', aExamples); </li></ul><ul><li>} </li></ul><ul><li>init(); </li></ul><ul><li></script> </li></ul>
  30. asynchronous JS example: menu.js <ul><li><script type=&quot;text/javascript&quot;> </li></ul><ul><li>var domscript = document.createElement('script'); </li></ul><ul><li>domscript.src = &quot;menu.js&quot;; </li></ul><ul><li>document.getElementsByTagName('head')[0].appendChild(domscript); </li></ul><ul><li>var aExamples = </li></ul><ul><li>[ </li></ul><ul><li>['couple-normal.php', 'Normal Script Src'], </li></ul><ul><li>['couple-xhr-eval.php', 'XHR Eval'], </li></ul><ul><li>... </li></ul><ul><li>['managed-xhr.php', 'Managed XHR'] </li></ul><ul><li>]; </li></ul><ul><li>function init() { </li></ul><ul><li>EFWS.Menu.createMenu('examplesbtn', aExamples); </li></ul><ul><li>} </li></ul><ul><li>init(); </li></ul><ul><li></script> </li></ul>script DOM element approach
  31. before after
  32. load scripts without blocking * Only other document.write scripts are downloaded in parallel (in the same script block). !IE
  33. asynchronous scripts wrap-up <ul><li>what about </li></ul><ul><li>inlined code </li></ul><ul><li>that depends on the script? </li></ul>
  34. <ul><li>what about </li></ul><ul><li>inlined code </li></ul><ul><li>that depends on the script? </li></ul>
  35. baseline coupling results (not good) * Scripts download in parallel regardless of the Defer attribute. need a way to load scripts asynchronously AND preserve order
  36. coupling techniques <ul><li>hardcoded callback </li></ul><ul><li>window onload </li></ul><ul><li>timer </li></ul><ul><li>degrading script tags </li></ul><ul><li>script onload </li></ul>
  37. technique 1: hardcoded callback <ul><li><script type=&quot;text/javascript&quot;> </li></ul><ul><li>var aExamples = [['couple-normal.php', 'Normal Script Src'], ...]; </li></ul><ul><li>function init() { </li></ul><ul><li>EFWS.Menu.createMenu('examplesbtn', aExamples); </li></ul><ul><li>} </li></ul><ul><li>var domscript = document.createElement('script'); </li></ul><ul><li>domscript.src = &quot;menu.js&quot;; </li></ul><ul><li>document.getElementsByTagName('head')[0].appendChild(domscript); </li></ul><ul><li></script> </li></ul><ul><li>init() is called from within menu.js </li></ul><ul><li>not very flexible </li></ul><ul><li>doesn't work for 3 rd party scripts </li></ul>
  38. technique 2: window onload <ul><li><iframe src=&quot;menu.php&quot; width=0 height=0 frameborder=0> </iframe> </li></ul><ul><li><script type=&quot;text/javascript&quot;> </li></ul><ul><li>var aExamples = [['couple-normal.php', 'Normal Script Src'], ...]; </li></ul><ul><li>function init() { </li></ul><ul><li>EFWS.Menu.createMenu('examplesbtn', aExamples); </li></ul><ul><li>} </li></ul><ul><li>if ( window.addEventListener ) { </li></ul><ul><li>window.addEventListener(&quot;load&quot;, init, false); </li></ul><ul><li>} </li></ul><ul><li>else if ( window.attachEvent ) { </li></ul><ul><li>window.attachEvent(&quot;onload&quot;, init); </li></ul><ul><li>} </li></ul><ul><li></script> </li></ul><ul><li>init() is called at window onload </li></ul><ul><li>must use async technique that blocks onload: </li></ul><ul><ul><li>Script in Iframe does this across most browsers </li></ul></ul><ul><li>init() called later than necessary </li></ul>
  39. technique 3: timer <ul><li><script type=&quot;text/javascript&quot;> </li></ul><ul><li>var domscript = document.createElement('script'); </li></ul><ul><li>domscript.src = &quot;menu.js&quot;; </li></ul><ul><li>document.getElementsByTagName('head')[0].appendChild(domscript); </li></ul><ul><li>var aExamples = [['couple-normal.php', 'Normal Script Src'], ...]; </li></ul><ul><li>function init() { </li></ul><ul><li>EFWS.Menu.createMenu('examplesbtn', aExamples); </li></ul><ul><li>} </li></ul><ul><li>function initTimer(interval) { </li></ul><ul><li>if ( &quot;undefined&quot; === typeof(EFWS) ) { </li></ul><ul><li>setTimeout(initTimer, interval); </li></ul><ul><li>} </li></ul><ul><li>else { </li></ul><ul><li>init(); </li></ul><ul><li>} </li></ul><ul><li>} </li></ul><ul><li>initTimer(300); </li></ul><ul><li></script> </li></ul><ul><li>load if interval too low, delay if too high </li></ul><ul><li>slight increased maintenance – EFWS </li></ul>
  40. John Resig's degrading script tags <ul><li><script src=&quot;menu-degrading.js&quot; type=&quot;text/javascript&quot;> </li></ul><ul><li>var aExamples = [['couple-normal.php', 'Normal Script Src'], ...]; </li></ul><ul><li>function init() { </li></ul><ul><li>EFWS.Menu.createMenu('examplesbtn', aExamples); </li></ul><ul><li>} </li></ul><ul><li>init(); </li></ul><ul><li></script> </li></ul>at the end of menu-degrading.js: var scripts = document.getElementsByTagName(&quot;script&quot;); var cntr = scripts.length; while ( cntr ) { var curScript = scripts[cntr-1]; if (curScript.src.indexOf(&quot;menu-degrading.js&quot;) != -1) { eval( curScript.innerHTML ); break; } cntr--; } http://ejohn.org/blog/degrading-script-tags/ cleaner clearer safer – inlined code not called if script fails no browser supports it
  41. technique 4: degrading script tags <ul><li><script type=&quot;text/javascript&quot;> </li></ul><ul><li>var aExamples = [['couple-normal.php', 'Normal Script Src'],...]; </li></ul><ul><li>function init() { </li></ul><ul><li>EFWS.Menu.createMenu('examplesbtn', aExamples); </li></ul><ul><li>} </li></ul><ul><li>var domscript = document.createElement('script'); </li></ul><ul><li>domscript.src = &quot;menu-degrading.js&quot;; </li></ul><ul><li>if ( -1 != navigator.userAgent.indexOf(&quot;Opera&quot;) ) { </li></ul><ul><li>domscript.innerHTML = &quot;init();&quot;; </li></ul><ul><li>} </li></ul><ul><li>else { </li></ul><ul><li>domscript.text = &quot;init();&quot;; </li></ul><ul><li>} </li></ul><ul><li>document.getElementsByTagName('head')[0].appendChild(domscript); </li></ul><ul><li></script> </li></ul><ul><li>elegant, flexible (cool!) </li></ul><ul><li>not well known </li></ul><ul><li>doesn't work for 3 rd party scripts (unless...) </li></ul>
  42. technique 5: script onload <ul><li><script type=&quot;text/javascript&quot;> </li></ul><ul><li>var aExamples = [['couple-normal.php', 'Normal Script Src'], ...]; </li></ul><ul><li>function init() { </li></ul><ul><li>EFWS.Menu.createMenu('examplesbtn', aExamples); </li></ul><ul><li>} </li></ul><ul><li>var domscript = document.createElement('script'); </li></ul><ul><li>domscript.src = &quot;menu.js&quot;; </li></ul><ul><li>domscript.onloadDone = false; </li></ul><ul><li>domscript.onload = function() { </li></ul><ul><li>if ( ! domscript.onloadDone ) { init(); } </li></ul><ul><li>domscript.onloadDone = true; </li></ul><ul><li>}; </li></ul><ul><li>domscript.onreadystatechange = function() { </li></ul><ul><li>if ( &quot;loaded&quot; === domscript.readyState ) { </li></ul><ul><li>if ( ! domscript.onloadDone ) { init(); } </li></ul><ul><li>domscript.onloadDone = true; </li></ul><ul><li>} </li></ul><ul><li>} </li></ul><ul><li>document.getElementsByTagName('head')[0].appendChild(domscript); </li></ul><ul><li></script> </li></ul><ul><li>pretty nice, medium complexity </li></ul>
  43. <ul><li>what about </li></ul><ul><li>multiple scripts </li></ul><ul><li>that depend on each other, </li></ul><ul><li>and inlined code </li></ul><ul><li>that depends on the scripts? </li></ul><ul><li>two solutions: </li></ul><ul><ul><li>Managed XHR </li></ul></ul><ul><ul><li>DOM Element and Doc Write </li></ul></ul>
  44. multiple script example: menutier.js <ul><li><script src=&quot;menu.js&quot; type=&quot;text/javascript&quot;></script> </li></ul><ul><li><script src=&quot;menutier.js&quot; type=&quot;text/javascript&quot;></script> </li></ul><ul><li><script type=&quot;text/javascript&quot;> </li></ul><ul><li>var aRaceConditions = [['couple-normal.php', 'Normal...]; </li></ul><ul><li>var aWorkarounds = [['hardcoded-callback.php', 'Hardcod...]; </li></ul><ul><li>var aMultipleScripts = [['managed-xhr.php', 'Managed XH...]; </li></ul><ul><li>var aLoadScripts = [['loadscript.php', 'loadScript'], ...]; </li></ul><ul><li>var aSubmenus = </li></ul><ul><li>[[&quot;Race Conditions&quot;, aRaceConditions], </li></ul><ul><li>[&quot;Workarounds&quot;, aWorkarounds], </li></ul><ul><li>[&quot;Multiple Scripts&quot;, aMultipleScripts], </li></ul><ul><li>[&quot;General Solution&quot;, aLoadScripts]]; </li></ul><ul><li>function init() { </li></ul><ul><li>EFWS.Menu.createTieredMenu('examplesbtn', aSubmenus); </li></ul><ul><li>} </li></ul><ul><li></script> </li></ul>
  45. technique 1: managed XHR <ul><li><script type=&quot;text/javascript&quot;> </li></ul><ul><li>var aRaceConditions = [['couple-normal.php', 'Normal...]; </li></ul><ul><li>var aWorkarounds = [['hardcoded-callback.php', 'Hardcod...]; </li></ul><ul><li>var aMultipleScripts = [['managed-xhr.php', 'Managed XH...]; </li></ul><ul><li>var aLoadScripts = [['loadscript.php', 'loadScript'], ...]; </li></ul><ul><li>var aSubmenus = [[&quot;Race Conditions&quot;, aRaceConditions], ...]; </li></ul><ul><li>function init() { </li></ul><ul><li>EFWS.Menu.createTieredMenu('examplesbtn', aSubmenus); </li></ul><ul><li>} </li></ul><ul><li>EFWS.Script.loadScriptXhrInjection(&quot;menu.js&quot;, null, true); </li></ul><ul><li>EFWS.Script.loadScriptXhrInjection(&quot;menutier.js&quot;, init, true); </li></ul><ul><li></script> </li></ul><ul><li>XHR Injection asynchronous technique does not preserve order – we have to add that </li></ul>before after
  46. EFWS.loadScriptXhrInjection <ul><li>// Load an external script. </li></ul><ul><li>// Optionally call a callback and preserve order. </li></ul><ul><li>loadScriptXhrInjection: function(url, onload, bOrder) { </li></ul><ul><li>var iQ = EFWS.Script.queuedScripts.length; </li></ul><ul><li>if ( bOrder ) { </li></ul><ul><li>var qScript = { response: null, onload: onload, done: false }; </li></ul><ul><li>EFWS.Script.queuedScripts[iQ] = qScript; </li></ul><ul><li>} </li></ul><ul><li>var xhrObj = EFWS.Script.getXHRObject(); </li></ul><ul><li>xhrObj.onreadystatechange = function() { </li></ul><ul><li>if ( xhrObj.readyState == 4 ) { </li></ul><ul><li>if ( bOrder ) { </li></ul><ul><li>EFWS.Script.queuedScripts[iQ].response = xhrObj.responseText; </li></ul><ul><li>EFWS.Script.injectScripts(); </li></ul><ul><li>} </li></ul><ul><li>else { </li></ul><ul><li>eval(xhrObj.responseText); </li></ul><ul><li>if ( onload ) { </li></ul><ul><li>onload(); </li></ul><ul><li>} </li></ul><ul><li>} </li></ul><ul><li>} </li></ul><ul><li>}; </li></ul><ul><li>xhrObj.open('GET', url, true); </li></ul><ul><li>xhrObj.send(''); </li></ul><ul><li>} </li></ul>process queue (next slide) or... eval now, call callback save response to queue add to queue (if bOrder)
  47. EFWS.injectScripts <ul><li>// Process queued scripts to see if any are ready to inject. </li></ul><ul><li>injectScripts: function() { </li></ul><ul><li>var len = EFWS.Script.queuedScripts.length; </li></ul><ul><li>for ( var i = 0; i < len; i++ ) { </li></ul><ul><li>var qScript = EFWS.Script.queuedScripts[i]; </li></ul><ul><li>if ( ! qScript.done ) { </li></ul><ul><li>if ( ! qScript.response ) { </li></ul><ul><li>// STOP! need to wait for this response </li></ul><ul><li>break; </li></ul><ul><li>} </li></ul><ul><li>else { </li></ul><ul><li>eval(qScript.response); </li></ul><ul><li>if ( qScript.onload ) { </li></ul><ul><li>qScript.onload(); </li></ul><ul><li>} </li></ul><ul><li>qScript.done = true; </li></ul><ul><li>} </li></ul><ul><li>} </li></ul><ul><li>} </li></ul><ul><li>} </li></ul>preserves external script order non-blocking works in all browsers couples with inlined code works with scripts across domains ready for this script, eval and call callback bail – need to wait to preserve order if not yet injected
  48. technique 2: DOM Element and Doc Write Firefox & Opera – use Script DOM Element IE – use document.write Script Tag Safari, Chrome – no benefit; rely on Safari 4 and Chrome 2
  49. EFWS.loadScripts <ul><li>loadScripts: function(aUrls, onload) { </li></ul><ul><li>// first pass: see if any of the scripts are on a different domain </li></ul><ul><li>var nUrls = aUrls.length; </li></ul><ul><li>var bDifferent = false; </li></ul><ul><li>for ( var i = 0; i < nUrls; i++ ) { </li></ul><ul><li>if ( EFWS.Script.differentDomain(aUrls[i]) ) { </li></ul><ul><li>bDifferent = true; </li></ul><ul><li>break; </li></ul><ul><li>} </li></ul><ul><li>} </li></ul><ul><li>// pick the best loading function </li></ul><ul><li>var loadFunc = EFWS.Script.loadScriptXhrInjection; </li></ul><ul><li>if ( bDifferent ) { </li></ul><ul><li>if ( -1 != navigator.userAgent.indexOf('Firefox') || </li></ul><ul><li>-1 != navigator.userAgent.indexOf('Opera') ) { </li></ul><ul><li>loadFunc = EFWS.Script.loadScriptDomElement; </li></ul><ul><li>} </li></ul><ul><li>else { </li></ul><ul><li>loadFunc = EFWS.Script.loadScriptDocWrite; </li></ul><ul><li>} </li></ul><ul><li>} </li></ul><ul><li>// second pass: load the scripts </li></ul><ul><li>for ( var i = 0; i < nUrls; i++ ) { </li></ul><ul><li>loadFunc(aUrls[i], ( i+1 == nUrls ? onload : null ), true); </li></ul><ul><li>} </li></ul><ul><li>} </li></ul>
  50. multiple scripts with dependencies <ul><li><script type=&quot;text/javascript&quot;> </li></ul><ul><li>var aRaceConditions = [['couple-normal.php', 'Normal...]; </li></ul><ul><li>var aWorkarounds = [['hardcoded-callback.php', 'Hardcod...]; </li></ul><ul><li>var aMultipleScripts = [['managed-xhr.php', 'Managed XH...]; </li></ul><ul><li>var aLoadScripts = [['loadscript.php', 'loadScript'], ...]; </li></ul><ul><li>var aSubmenus = [[&quot;Race Conditions&quot;, aRaceConditions], ...]; </li></ul><ul><li>function init() { </li></ul><ul><li>EFWS.Menu.createTieredMenu('examplesbtn', aSubmenus); </li></ul><ul><li>} </li></ul><ul><li>EFWS.Script.loadScripts([&quot;menu.js&quot;, &quot;menutier.js&quot;], init); </li></ul><ul><li></script> </li></ul><ul><li>scripts on same domain: </li></ul><ul><ul><li>order preserved, no blocking </li></ul></ul><ul><li>scripts on different domain: </li></ul><ul><ul><li>order preserved: all </li></ul></ul><ul><ul><li>loads scripts in parallel: all except Saf3, Chr1 </li></ul></ul><ul><ul><li>load script and image in parallel: FF, Saf4, Chr2 </li></ul></ul>
  51. asynchronous scripts wrap-up
  52. case study: Google Analytics <ul><li>recommended pattern: 1 </li></ul><ul><li><script type=&quot;text/javascript&quot;> </li></ul><ul><li>var gaJsHost = ((&quot;https:&quot; == document.location.protocol) ? &quot;https://ssl.&quot; : &quot;http://www.&quot;); </li></ul><ul><li>document.write(unescape(&quot;%3Cscript src='&quot; + gaJsHost + &quot;google-analytics.com/ga.js' type='text/javascript'%3E%3C/script%3E&quot;)); </li></ul><ul><li></script> </li></ul><ul><li><script type=&quot;text/javascript&quot;> </li></ul><ul><li>var pageTracker = _gat._getTracker(&quot;UA-xxxxxx-x&quot;); </li></ul><ul><li>pageTracker._trackPageview(); </li></ul><ul><li></script> </li></ul><ul><li>document.write Script Tag approach blocks other resources </li></ul>1 http://www.google.com/support/analytics/bin/answer.py?hl=en&answer=55488
  53. case study: dojox.analytics.Urchin 1 <ul><li>_loadGA: function(){ </li></ul><ul><li>var gaHost = (&quot;https:&quot; == document.location.protocol) ? </li></ul><ul><li>&quot;https://ssl.&quot; : &quot;http://www.&quot;; </li></ul><ul><li>dojo.create('script', { </li></ul><ul><li>src: gaHost + &quot;google-analytics.com/ga.js&quot; </li></ul><ul><li>}, dojo.doc.getElementsByTagName(&quot;head&quot;)[0]); </li></ul><ul><li>setTimeout(dojo.hitch(this, &quot;_checkGA&quot;), this.loadInterval); </li></ul><ul><li>}, </li></ul><ul><li>_checkGA: function(){ </li></ul><ul><li>setTimeout(dojo.hitch(this, !window[&quot;_gat&quot;] ? &quot;_checkGA&quot; : &quot;_gotGA&quot;), this.loadInterval); </li></ul><ul><li>}, </li></ul><ul><li>_gotGA: function(){ </li></ul><ul><li>this.tracker = _gat._getTracker(this.acct); ... </li></ul><ul><li>} </li></ul><ul><li>Script DOM Element approach </li></ul><ul><li>&quot;timer&quot; coupling technique (script onload better) </li></ul>1 http://docs.dojocampus.org/dojox/analytics/Urchin
  54. asynchronous loading & coupling <ul><li>async technique: Script DOM Element </li></ul><ul><ul><li>easy, cross-browser </li></ul></ul><ul><ul><li>doesn't ensure script order </li></ul></ul><ul><li>coupling technique: script onload </li></ul><ul><ul><li>fairly easy, cross-browser </li></ul></ul><ul><ul><li>ensures execution order for external script and inlined code </li></ul></ul>
  55. bad: stylesheet followed by inline script <ul><li>browsers download stylesheets in parallel with other resources that follow... </li></ul><ul><li>...unless the stylesheet is followed by an inline script </li></ul><ul><li>http://stevesouders.com/cuzillion/?ex=10021 </li></ul><ul><li>best to move inline scripts above stylesheets or below other resources </li></ul><ul><li>use Link, not @import </li></ul>
  56. don't scatter inline scripts eBay MSN MySpace Wikipedia
  57. iframes: most expensive DOM element <ul><li>load 100 empty elements of each type </li></ul><ul><li>tested in all major browsers 1 </li></ul>1 IE 6, 7, 8; FF 2, 3.0, 3.1b2; Safari 3.2, 4; Opera 9.63, 10; Chrome 1.0, 2.0
  58. iframes block onload <ul><li>parent's onload doesn't fire until iframe and all its components are downloaded </li></ul><ul><li>workaround for Safari and Chrome: set iframe src in JavaScript </li></ul><ul><li><iframe id=iframe1 src=&quot;&quot;></iframe> </li></ul><ul><li><script type=&quot;text/javascript&quot;> </li></ul><ul><li>document.getElementById('iframe1').src=&quot; url &quot;; </li></ul><ul><li></script> </li></ul>
  59. scripts block iframe <ul><li>no surprise – scripts in the parent block the iframe from loading </li></ul>IE Firefox Safari Chrome Opera script script script
  60. stylesheets block iframe (IE, FF) <ul><li>surprise – stylesheets in the parent block the iframe or its resources in IE & Firefox </li></ul>IE Firefox Safari Chrome Opera stylesheet stylesheet stylesheet
  61. stylesheets after iframe still block (FF) <ul><li>surprise – even moving the stylesheet after the iframe still causes the iframe's resources to be blocked in Firefox </li></ul>IE Firefox Safari Chrome Opera stylesheet stylesheet stylesheet
  62. iframes: no free connections <ul><li>iframe shares connection pool with parent (here – 2 connections per server in IE 7) </li></ul>iframe parent
  63. flush the document early <ul><li>gotchas: </li></ul><ul><ul><li>PHP output_buffering – ob_flush() </li></ul></ul><ul><ul><li>Transfer-Encoding: chunked </li></ul></ul><ul><ul><li>gzip – Apache's DeflateBufferSize before 2.2.8 </li></ul></ul><ul><ul><li>proxies and anti-virus software </li></ul></ul><ul><ul><li>browsers – Safari (1K), Chrome (2K) </li></ul></ul><ul><li>other languages: </li></ul><ul><ul><li>$| or FileHandle autoflush (Perl), flush (Python), ios.flush (Ruby) </li></ul></ul>call PHP's flush() html image image script html image image script
  64. flushing and domain blocking <ul><li>you might need to move flushed resources to a domain different from the HTML doc </li></ul>case study: Google search blocked by HTML document different domains html image image script html image image script google image image script image 204
  65. takeaways <ul><li>focus on the frontend </li></ul><ul><li>run YSlow: http://developer.yahoo.com/yslow </li></ul><ul><li>this year's focus: JavaScript </li></ul><ul><li>speed matters </li></ul>
  66. impact on revenue <ul><li>Google: </li></ul><ul><li>Yahoo: </li></ul><ul><li>Amazon: </li></ul>1 http://home.blarg.net/~glinden/StanfordDataMining.2006-11-29.ppt 2 http://www.slideshare.net/stoyan/yslow-20-presentation +500 ms  -20% traffic 1 +400 ms  -5-9% full-page traffic 2 +100 ms  -1% sales 1
  67. cost savings <ul><li>hardware – reduced load </li></ul><ul><li>bandwidth – reduced response size </li></ul>http://billwscott.com/share/presentations/2008/stanford/HPWP-RealWorld.pdf
  68. <ul><li>if you want </li></ul><ul><ul><li>better user experience </li></ul></ul><ul><ul><li>more revenue </li></ul></ul><ul><ul><li>reduced operating expenses </li></ul></ul><ul><li>the strategy is clear </li></ul><ul><li>Even Faster Web Sites </li></ul>
  69. Steve Souders [email_address] http://stevesouders.com/docs/sxsw-20090314.ppt

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