Even Faster Web Sites

1. Even Faster Web Sites http://stevesouders.com/docs/jquery-20090913.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

5. Sept 2007

8. June 2009

9. 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

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

11. 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

12. initial payload and execution 26% avg 252K avg

13. 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?

14. 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)

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

16. 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

17. 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

18. 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');

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

20. 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

21. 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

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

23. 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

25. 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>

26. before after

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

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

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

30. 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

31. 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!

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

33. 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:

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

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

36. book signing now Steve Souders souders@google.com http://stevesouders.com/docs/jquery-20090913.ppt