Life's too short, write fast code part 1

1. Life's too short,write fast codepart 1 Steve Souders souders@google.com http://stevesouders.com/docs/myspace-20081024.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. 14 Rules • 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

6. YSlow High Performance Web Sites

7. http://conferences.oreilly.com/velocity/ June 22-24, 2009

9. High Performance Web Sites, Vol 2 } • Split the initial payload • Load scripts without blocking • Don't scatter inline scripts • Split dominant domains • Make static content cookie-free • Reduce cookie weight • Minify CSS • Optimize images • Use iframes sparingly • To www or not to www part 1

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

11. Scripts Block <script src="A.js"> blocks parallel downloads and rendering http://stevesouders.com/cuzillion/?ex=10008 What's "Cuzillion"?

12. Initial Payload and Execution 26% avg 252K avg

13. Split 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. Advanced Script Loading 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 http://stevesouders.com/cuzillion/?ex=10009

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

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'); 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("<scr" + "ipt type='text/javascript' src='A.js'>" + "</scr" + "ipt>"); 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

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 • Ensure scripts execute in order: • necessary when scripts have dependencies • IE: http://stevesouders.com/cuzillion/?ex=10017 • FF: http://stevesouders.com/cuzillion/?ex=10018 • Avoid scripts executing in order: • faster – first script back is executed immediately • http://stevesouders.com/cuzillion/?ex=10019

25. Summary of Traits *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 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

27. Load 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?

28. Inline Scripts after Stylesheets Block Downloading Firefox 3 and IE download stylesheets in parallel ...unless the stylesheet is followed by an inline script http://stevesouders.com/cuzillion/?ex=10021 best to move inline scripts above stylesheets or below other resources use Link, not @import

29. Examples of Scattered Scripts MSN Wikipedia eBay MySpace

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

31. Announcement 1: UA Profiler tracks browser performance traits http://stevesouders.com/ua/ go to the test page your browser automatically walks through the tests (requires JS) results recorded and shared publicly currently 2K+ tests, 1K+ unique testers, 100+ browsers help out by running the test!

32. Measuring Performance Episodes dev box synthetic testing bucket testing real user data Hammerhead

33. Announcement 2: Hammerhead"moving performance testing upstream" http://stevesouders.com/hammerhead/ Firebug extension load M URLs N times, empty & primed cache record average & median time add'l features: export data load time measurement modal cache clearing combine with bandwidth throttler

34. Splash YSlow: 74 unused JS: ~87% unused CSS: ~61%, 47K

35. Home YSlow: 49 unused JS: ~86% unused CSS: ~61%, 44K

36. Profile YSlow: 81 unused JS: ~91% unused CSS: ~69%, 43K

37. Splash YSlow: 60 unused JS: ~89% unused CSS: ~65%, 36K

38. MySpace performance analysis analyzed Splash, Home, Profile, More Pics the good • future Expires (10 days) • gzip • some CSS sprites • no CSS expressions • no redirects • bad ETags syntax changed

39. MySpace performance analysis the opportunities • YSlow: 74, 49, 81 60 added myspacecdn.com, x.myspace.com to CDN list • ads • combine scripts & stylesheets • split JS payload: ~90% unused (~360K uncomp) • remove unused CSS: ~65% (~50K uncomp) • move scripts to the bottom or load w/o blocking • minify scripts

40. HTTP waterfall

41. Takeaways focus on the frontend run YSlow: http://developer.yahoo.com/yslow this year's focus: JavaScript Split the Initial Payload Load Scripts without Blocking Don't Scatter Inline Scripts speed matters life's too short, write fast code

42. Steve Souders souders@google.com http://stevesouders.com/docs/myspace-20081024.ppt