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Even Faster Web Sites

Even Faster Web Sites

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Even Faster Web Sites

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  1. Even Faster Web Sites http://stevesouders.com/docs/tae-20090914.ppt Disclaimer: This content does not necessarily reflect the opinions of my employer.

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

  3. Make fewer HTTP requests • Use a CDN • Add an Expires header • Gzip components • Put stylesheets at the top • Put scripts at the bottom • Avoid CSS expressions • Make JS and CSS external • Reduce DNS lookups • Minify JS • Avoid redirects • Remove duplicate scripts • Configure ETags • Make AJAX cacheable 14 Rules

  4. web performance guy

  5. 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

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

  7. scripts block <script src="A.js"> blocks parallel downloads and rendering 9 secs: IE 6-7, FF 3.0, Chr 1, Op 9-10, Saf 3 7 secs: IE 8, FF 3.5, Chr 2, Saf 4

  8. MSN.com: parallel scripts 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)

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

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

  11. XHR Injection varxhrObj = 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

  12. Script in Iframe <iframe src='A.html' width=0 height=0 frameborder=0 id=frame1></iframe> • 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');

  13. 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

  14. Script Defer <script defer src='A.js'></script> supported in IE and FF 3.1+ script and main page domains can differ no need to refactor JavaScript

  15. document.write Script Tag document.write("<script type='text/javascript' src='A.js'> <\/script>"); parallelization only works in IE parallel downloads for scripts, nothing else all document.writes must be in same script block

  16. browser busy indicators

  17. Load Scripts Without Blocking *Only other document.write scripts are downloaded in parallel (in the same script block).

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

  19. menu.js image.gif

  20. asynchronous JS example: menu.js script DOM element approach <script type="text/javascript"> vardomscript = document.createElement('script'); domscript.src = "menu.js"; document.getElementsByTagName('head')[0].appendChild(domscript); varaExamples = [ ['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>

  21. before menu.js image.gif menu.js after image.gif

  22. Loading Scripts Without Blocking !IE *Only other document.write scripts are downloaded in parallel (in the same script block).

  23. what about inlined code that depends on the script?

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

  25. John Resig's degrading script tags at the end of menu-degrading.js: var scripts = document.getElementsByTagName("script"); varcntr = scripts.length; while ( cntr ) { varcurScript = 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 <script src="menu-degrading.js" type="text/javascript"> varaExamples = [['couple-normal.php', 'Normal Script Src'], ...]; function init() { EFWS.Menu.createMenu('examplesbtn', aExamples); } init(); </script> http://ejohn.org/blog/degrading-script-tags/

  26. technique 4: degrading script tags <script type="text/javascript"> varaExamples = [['couple-normal.php', 'Normal Script Src'],...]; function init() { EFWS.Menu.createMenu('examplesbtn', aExamples); } vardomscript = 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); </script> elegant, flexible (cool!) not well known doesn't work for 3rd party scripts (unless...)

  27. technique 5: script onload <script type="text/javascript"> varaExamples = [['couple-normal.php', 'Normal Script Src'], ...]; function init() { EFWS.Menu.createMenu('examplesbtn', aExamples); } vardomscript = 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); </script> pretty nice, medium complexity menu.js image.gif

  28. 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!

  29. flushing the document early html image image script call PHP's flush() html image image script gotchas: • PHP output_buffering – ob_flush() • Transfer-Encoding: chunked • gzip – Apache's DeflateBufferSize before 2.2.8 • proxies and anti-virus software • browsers – Safari (1K), Chrome (2K) other languages: • $| or FileHandleautoflush (Perl), flush (Python), ios.flush (Ruby)

  30. flushing and domain blocking html image image script blocked by HTML document html image image script different domains you might need to move flushed resources to a domain different from the HTML doc

  31. successful flushing http://www.google.com/images/nav_logo4.png google image image script image 204 Google Search external resource downloaded early content visible to the user

  32. performance analyzers (HPWS)

  33. performance analyzers (EFWS)

  34. performance analyzers (other)

  35. takeaways focus on the frontend run YSlow (http://developer.yahoo.com/yslow) and Page Speed! (http://code.google.com/speed/page-speed/) speed matters

  36. impact on revenue +2000 ms  -4.3% revenue/user1 +400 ms  -5-9% full-page traffic2 +400 ms  -0.59% searches/user1 fastest users+50% page views3 -5000 ms +7-12% revenue4 1 http://en.oreilly.com/velocity2009/public/schedule/detail/8523 2 http://www.slideshare.net/stoyan/yslow-20-presentation 3 http://en.oreilly.com/velocity2009/public/schedule/detail/7579 4 http://en.oreilly.com/velocity2009/public/schedule/detail/7709 Bing: Yahoo: Google: AOL: Shopzilla:

  37. cost savings hardware – reduced load • Shopzilla – 50% fewer servers bandwidth – reduced response size http://billwscott.com/share/presentations/2008/stanford/HPWP-RealWorld.pdf

  38. if you want • better user experience • more revenue • reduced operating costs the strategy is clear Even Faster Web Sites

  39. book signing immediately 3:30-3:50 Steve Souders souders@google.com http://stevesouders.com/docs/tae-20090914.ppt