Even Faster Web Sites

1. Even Faster Web Sites Steve Souders souders@google.com http://stevesouders.com/docs/shopping-com-20090520.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. time spent on the frontend April 2008

4. 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

5. 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

9. Sept 2007

10. June 2009

11. 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

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

13. 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 http://stevesouders.com/cuzillion/?ex=10008 What's Cuzillion?

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

15. 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?

16. 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)

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

18. 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 http://stevesouders.com/cuzillion/?ex=10009

19. 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 http://stevesouders.com/cuzillion/?ex=10015

20. 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'); http://stevesouders.com/cuzillion/?ex=10012

21. 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

22. 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

23. 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 http://stevesouders.com/cuzillion/?ex=10014

24. browser busy indicators

25. browser busy indicators good to show busy indicators when the user needs feedback bad when downloading in the background

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

27. 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

29. 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>

30. before after

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

32. what about • inlined code • that depends on the script?

33. coupling techniques • hardcoded callback • window onload • timer • degrading script tags • script onload

34. 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

35. 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!

36. flushing the document early • 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) html image image script call PHP's flush() html image image script

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

38. http://www.shopping.com/xFS?KW=sony&CLT=SCH http://www.shopping.com/xPO-Nike_Mens_Super_Bad_Ft_Football_Cleats http://www.shopping.com/

39. http://www.shopping.com • 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

40. http://www.shopping.com/xFS?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

41. http://www.shopping.com/xPO-Nike_Mens_Super_Bad_Ft_Football_Cleatshttp://www.shopping.com/xPO-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

42. takeaways • focus on the frontend • run YSlow: http://developer.yahoo.com/yslow • speed matters

43. impact on revenue • Google: • Yahoo: • Amazon: +500 ms  -20% traffic1 +400 ms  -5-9% full-page traffic2 +100 ms  -1% sales1 1 http://home.blarg.net/~glinden/StanfordDataMining.2006-11-29.ppt 2 http://www.slideshare.net/stoyan/yslow-20-presentation

44. cost savings • hardware – reduced load • bandwidth – reduced response size http://billwscott.com/share/presentations/2008/stanford/HPWP-RealWorld.pdf

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

46. Steve Souders souders@google.com http://stevesouders.com/docs/shopping-com-20090520.ppt