Even Faster Web Sites

1. Even Faster Web Sites Steve Souders souders@google.com http://stevesouders.com/docs/teched-20090512.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. Simplifying CSS Selectors rule selector • #toc > LI { font-weight: bold; } simple selectors declaration block combinator

37. types of CSS selectors • ID selectors • #toc { margin-left: 20px; } • element whose ID attribute has the value "toc" • class selectors • .chapter { font-weight: bold; } • elements with class=chapter • type selectors • A { text-decoration: none; } • all A elements in the document tree • http://www.w3.org/TR/CSS2/selector.html

38. types of CSS selectors • adjacent sibling selectors • H1 + #toc { margin-top: 40px; } • an element with ID=toc that immediately follows an H1 • child selectors • #toc > LI { font-weight: bold; } • all LI elements whose parent has id="toc" • descendant selectors • #toc A { color: #444; } • all A elements that have id="toc" as an ancestor

39. types of CSS selectors • universal selectors • * { font-family: Arial; } • all elements • attribute selectors • [href="#index"] { font-style: italic; } • all elements where the href attribute is "#index" • psuedo classes and elements • A:hover { text-decoration: underline; } • non-DOM behavior • others: :visited, :link, :active, :focus, :first-child, :before, :after

40. writing efficient CSS https://developer.mozilla.org/en/Writing_Efficient_CSS • "The style system matches a rule by starting with the rightmost selector and moving to the left through the rule's selectors. As long as your little subtree continues to check out, the style system will continue moving to the left until it either matches the rule or bails out because of a mismatch." • #toc > LI { font-weight: bold; } find every LI whose parent is id="toc" • #toc A { color: #444; } find every A and climb its ancestors until id="toc" or DOM root (!) is found

41. writing efficient CSS • avoid universal selectors • don't qualify ID selectors • bad: DIV #navbar {} • good: #navbar {} • don't qualify class selectors • bad: LI .tight {} • good: .li-tight {} • make rules as specific as possible • bad: #navbar A {} • good: .a-navbar {} https://developer.mozilla.org/en/Writing_Efficient_CSS

42. writing efficient CSS • avoid descendant selectors • bad: UL LI A {} • better: UL > LI > A {} • avoid tag-child selectors • bad: UL > LI > A {} • best: .li-anchor {} • be wary of child selectors • rely on inheritance • http://www.w3.org/TR/CSS21/propidx.html https://developer.mozilla.org/en/Writing_Efficient_CSS David Hyatt 4/21/2000

43. testing massive CSS • 20K A elements • no style: control • tag: • A {} • class: • .a00001 {} • .a20000 {} • descender: • DIV DIVDIV P A.a00001 {} • child: • DIV > DIV > DIV > P > A.a00001 {} • http://jon.sykes.me/153/more-css-performance-testing-pt-3

44. CSS performance isn't linear • IE 7 "cliff" at 18K rules

45. real world levels of CSS

46. testing typical CSS 1K rules (vs. 20K) same amount of CSS in all test pages 30 ms avg delta • "costly"selectors aren't always costly (at typical levels) • are these selectors "costly"? • DIV DIVDIV P A.class0007 { ... } http://www.stevesouders.com/blog/2009/03/10/performance-impact-of-css-selectors/

47. testing expensive selectors 1K rules (vs. 20K) same amount of CSS in all test pages 2126 ms avg delta! truly expensive selector A.class0007 * { ... } • compare to: • DIV DIVDIV P A.class0007 { ... } the key is the key selector – the rightmost argument

48. selectors to avoid • A.class0007 DIV { ... } • #id0007 > A { ... } • .class0007 [href] { ... } • DIV:first-child { ... }

49. reflow time vs. load time • reflow – time to apply CSS, re-layout elements, and repaint • triggered by DHTML: • elem.className = "newclass"; • elem.style.cssText = "color: red"; • elem.style.padding = "8px"; • elem.style.display = ""; • reflow can happen multiple times for long-lasting Web 2.0 apps

50. reflow time by browser • reflow performance varies by browser and action • "1x" is 1-6 seconds depending on browser (1K rules)