1. Steve Souders souders@google.com http://stevesouders.com/docs/cbs-20090209.ppt Even Faster Websites Disclaimer: This content does not necessarily reflect the opinions of my employer.

2. 17% 83% iGoogle, primed cache The Importance of Frontend Performance 9%91% iGoogle, empty cache

3. Time Spent on the Frontend Empty CachePrimed Cache www.aol.com97% www.ebay.com95%81% www.facebook.com95%81% www.google.com/search47%0% search.live.com/results67%0% www.msn.com98%94% www.myspace.com98% en.wikipedia.org/wiki94%91% www.yahoo.com97%96% www.youtube.com98%97% 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 1.Make fewer HTTP requests 2.Use a CDN 3.Add an Expires header 4.Gzip components 5.Put stylesheets at the top 6.Put scripts at the bottom 7.Avoid CSS expressions 8.Make JS and CSS external 9.Reduce DNS lookups 10.Minify JS 11.Avoid redirects 12.Remove duplicate scripts 13.Configure ETags 14.Make AJAX cacheable

6. High Performance Web Sites YSlow

7. http://en.oreilly.com/velocity2009 June 22-24, 2009

9. Even Faster Websites 1.Split the initial payload 2.Load scripts without blocking 3.Don't scatter inline scripts 4.Couple asynchronous scripts 5.Split dominant domains 6.Simplify CSS Selectors 7.Use iframes sparingly 8.Flush the document early O'Reilly, Q2 2009

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

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

12. a tool for quickly constructing web pages to see how components interact Open Source http://stevesouders.com/cuzillion/ Cuzillion 'cuz there are a zillion pages to check

13. JavaScript Functions Executed before onload www.aol.com115K30% www.ebay.com183K44% www.facebook.com1088K 9% www.google.com/search15K45% search.live.com/results17K24% www.msn.com131K31% www.myspace.com297K18% en.wikipedia.org/wiki114K32% www.yahoo.com321K13% www.youtube.com240K18% 26% avg 252K avg Initial Payload and Execution

14. 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?

15. 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) MSN.com: Parallel Scripts

16. Advanced Script Loading XHR Eval XHR Injection Script in Iframe Script DOM Element Script Defer document.write Script Tag

17. 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

18. 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

19. Script in Iframe <iframe src='A.html' width=0 height=0 frameborder=0 id=frame1> 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

20. 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

21. Script Defer 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

22. document.write Script Tag document.write("<scr" + "ipt type='text/javascript' src='A.js'>" + " "); 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

23. Browser Busy Indicators

24. status bar progress bar logocursor block render block onload normal Script Src FFIE,FF FFIE,FF XHR Eval no XHR Injection no Script in Iframe IE,FFFFIE,FFFFnoIE,FF Script DOM Element FF noFF Script Defer FF IE,FF document.write Script Tag FFIE,FF FFIE,FF good to show busy indicators when the user needs feedback bad when downloading in the background

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

26. Summary of Traits || down- loads domains can differ existing scripts browser busy ensures order size (bytes) normal Script Src noyes IE,FF ~50 XHR Eval IE,FFno ~500 XHR Injection IE,FFnoyesno ~500 Script in Iframe IE,FFno IE,FFno~50 Script DOM Element IE,FFyes FF ~200 Script Defer IEyes IE,FFIE~50 document.write Script Tag IE * yes IE,FFIE~100 * 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 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 orderno order no busy show busy no busy preserve order

28. 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?

29. Inline Scripts Block long executing inline scripts block rendering and downloads http://stevesouders.com/cuzillion/?ex=10035 workarounds: initiate execution with setTimeout (>250 for FF, nglayout.initialpaint.delay ) move JavaScript to external script with advanced downloading techniques use Defer attribute (IE only)

30. 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

31. eBay MSN MySpace Wikipedia Examples of Scattered Scripts

32. 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

33. 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 13K+ tests, 9K+ unique testers, 50+ browsers help out by running the test!

34. Measuring Performance Episodes dev boxsynthetic testing bucket testing real user data Hammerhead

35. 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

36. CNet Performance Analysis cool –flushed document –HTTP/1.0 downgrade opportunities –load oreo.moo.rb.combined.js async –split i.i.com.com across two domains –concatenate 10 scripts –sprite 25 CSS background images –30 resources with short Expires –62% (62K) of CSS not used requests: 107 load time: 3.7 secs xfer size: 436K YSlow: F (48)

37. BNet Performance Analysis cool –flushed document –@import stylesheets opportunities –compress 235K (16 files) –sprite 57 CSS background images –concatenate 12 scripts, 6 stylesheets –optimize images (30K, 16%) –106 resources with short Expires –60% (29K) of CSS not used –remove ETags requests: 149 load time: 5.9 secs xfer size: 759K YSlow: F (26)

38. cool –flushed document opportunities –compress 151K (11 files) –move inline script above stylesheets –concatenate 16 scripts –sprite 26 CSS background images –optimize images (104K, 28%) –move www.cbssports.com images to a CDN –split images.cbssports.com across two domains –almost all resources have a short Expires –49% (24K) of CSS not used –minify 63K (8 scripts) –remove ETags requests: 99 load time: 8.2 secs xfer size: 689K YSlow: F (31) CBSSports Performance Analysis

39. Takeaways focus on the frontend run YSlow: http://developer.yahoo.com/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

40. Impact on Revenue Google: Yahoo: Amazon: 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

41. Cost Savings hardware – reduced load bandwidth – reduced response size http://billwscott.com/share/presentations/2008/stanford/HPWP-RealWorld.pdf

42. if you want better user experience more revenue reduced operating expenses the strategy is clear Even Faster Websites

43. Steve Souders souders@google.com http://stevesouders.com/docs/cbs-20090209.ppt