1.Steve Souders [email_address] http://stevesouders.com/docs/sxsw-20090314.ppt Even Faster Web Sites Disclaimer:This content does not necessarily reflect the opinions of my employer.

2. the importance of frontend performance 17% 83% iGoogle, primed cache 9% 91% iGoogle, empty cache 3. time spent on the frontend April 2008 Empty Cache Primed Cache www.aol.com 97% 97% www.ebay.com 95% 81% www.facebook.com 95% 81% www.google.com/search 47% 0% search.live.com/results 67% 0% www.msn.com 98% 94% www.myspace.com 98% 98% en.wikipedia.org/wiki 94% 91% www.yahoo.com 97% 96% www.youtube.com 98% 97% 4. 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

5. 6. 7. 8. 25% discount code: "ssouders25" 9. Sept 2007 10. June 2009 11. Even Faster Websites Split the initial payload Load scripts without blocking Couple asynchronous scripts Don't scatter inline scripts Split the dominant domain Flush the document early Use iframes sparingly Simplify CSS Selectors Ajax performance (Doug Crockford) Writing efficient JavaScript (Nicholas Zakas) Creating responsive web apps (Ben Galbraith, Dion Almaer) Comet (Dylan Schiemann) Beyond Gzipping (Tony Gentilcore) Optimize Images (Stoyan Stefanov, Nicole Sullivan) 12. why focus on JavaScript? AOL eBay Facebook MySpace Wikipedia Yahoo! YouTube 13. scripts block 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.writeScript Tag document.write ("" + "" + "ipt>"); parallelization only works in IE parallel downloads for scripts, nothing else alldocument.write s must be in same script block http://stevesouders.com/cuzillion/?ex=10014 22. browser busy indicators 23. browser busy indicators goodto show busy indicators when the user needs feedback badwhen 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. load scripts without blocking * 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 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 order no order no busy show busy show busy no busy preserve order 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. 29. synchronous JS example: menu.js

var aExamples =

[

['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();

30. asynchronous JS example: menu.js

var domscript = document.createElement('script');

domscript.src = "menu.js";

document.getElementsByTagName('head')[0].appendChild(domscript);

var aExamples =

[

['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 DOM element approach 31. before after 32. load scripts without blocking * Only other document.write scripts are downloaded in parallel (in the same script block). !IE 33. asynchronous scripts wrap-up

what about

inlined code

that depends on the script?

34.

what about

inlined code

that depends on the script?

35. baseline coupling results (not good) *Scripts download in parallel regardless of the Defer attribute. need a way to load scripts asynchronously AND preserve order 36. coupling techniques

hardcoded callback

window onload

timer

degrading script tags

script onload

37. technique 1: hardcoded callback

var aExamples = [['couple-normal.php', 'Normal Script Src'], ...];

function init() {

EFWS.Menu.createMenu('examplesbtn', aExamples);

}

var domscript = document.createElement('script');

domscript.src = "menu.js";

document.getElementsByTagName('head')[0].appendChild(domscript);

init() is called from within menu.js

not very flexible

doesn't work for 3 rdparty scripts

38. technique 2: window onload

var aExamples = [['couple-normal.php', 'Normal Script Src'], ...];

function init() {

EFWS.Menu.createMenu('examplesbtn', aExamples);

}

if ( window.addEventListener ) {

window.addEventListener("load", init, false);

}

else if ( window.attachEvent ) {

window.attachEvent("onload", init);

}

init() is called at window onload

must use async technique that blocks onload:

• Script in Iframe does this across most browsers

init() called later than necessary

39. technique 3: timer

var domscript = document.createElement('script');

domscript.src = "menu.js";

document.getElementsByTagName('head')[0].appendChild(domscript);

var aExamples = [['couple-normal.php', 'Normal Script Src'], ...];

function init() {

EFWS.Menu.createMenu('examplesbtn', aExamples);

}

function initTimer(interval) {

if ( "undefined" === typeof(EFWS) ) {

setTimeout(initTimer, interval);

}

else {

init();

}

}

initTimer(300);

load ifintervaltoo low, delay if too high

slight increased maintenance EFWS

40. John Resig's degrading script tags

var aExamples = [['couple-normal.php', 'Normal Script Src'], ...];

function init() {

EFWS.Menu.createMenu('examplesbtn', aExamples);

}

init();

at the end of menu-degrading.js: var scripts = document.getElementsByTagName("script"); var cntr = scripts.length; while ( cntr ) { var curScript = scripts[cntr-1]; if (curScript.src.indexOf("menu-degrading.js") != -1) { eval( curScript.innerHTML ); break; } cntr--; } http://ejohn.org/blog/degrading-script-tags/ cleaner clearer safer inlined code not called if script fails no browser supports it 41. technique 4: degrading script tags

var aExamples = [['couple-normal.php', 'Normal Script Src'],...];

function init() {

EFWS.Menu.createMenu('examplesbtn', aExamples);

}

var domscript = document.createElement('script');

domscript.src = "menu-degrading.js";

if ( -1 != navigator.userAgent.indexOf("Opera") ) {

domscript.innerHTML = "init();";

}

else {

domscript.text = "init();";

}

document.getElementsByTagName('head')[0].appendChild(domscript);

elegant, flexible (cool!)

not well known

doesn't work for 3 rdparty scripts (unless...)

42. technique 5: script onload

var aExamples = [['couple-normal.php', 'Normal Script Src'], ...];

function init() {

EFWS.Menu.createMenu('examplesbtn', aExamples);

}

var domscript = 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);

pretty nice, medium complexity

43.

what about

multiple scripts

that depend on each other,

and inlined code

that depends on the scripts?

two solutions:

• Managed XHR

• DOM Element and Doc Write

44. multiple script example: menutier.js

var aRaceConditions = [['couple-normal.php', 'Normal...];

var aWorkarounds = [['hardcoded-callback.php', 'Hardcod...];

var aMultipleScripts = [['managed-xhr.php', 'Managed XH...];

var aLoadScripts = [['loadscript.php', 'loadScript'], ...];

var aSubmenus =

[["Race Conditions", aRaceConditions],

["Workarounds", aWorkarounds],

["Multiple Scripts", aMultipleScripts],

["General Solution", aLoadScripts]];

function init() {

EFWS.Menu.createTieredMenu('examplesbtn', aSubmenus);

}

45. technique 1: managed XHR

var aRaceConditions = [['couple-normal.php', 'Normal...];

var aWorkarounds = [['hardcoded-callback.php', 'Hardcod...];

var aMultipleScripts = [['managed-xhr.php', 'Managed XH...];

var aLoadScripts = [['loadscript.php', 'loadScript'], ...];

var aSubmenus = [["Race Conditions", aRaceConditions], ...];

function init() {

EFWS.Menu.createTieredMenu('examplesbtn', aSubmenus);

}

EFWS.Script.loadScriptXhrInjection("menu.js", null, true);

EFWS.Script.loadScriptXhrInjection("menutier.js", init, true);

XHR Injection asynchronous technique does not preserve order we have to add that

before after 46. EFWS.loadScriptXhrInjection

// Load an external script.

// Optionally call a callback and preserve order.

loadScriptXhrInjection: function(url, onload, bOrder) {

var iQ = EFWS.Script.queuedScripts.length;

if ( bOrder ) {

var qScript = { response: null, onload: onload, done: false };

EFWS.Script.queuedScripts[iQ] = qScript;

}

var xhrObj = EFWS.Script.getXHRObject();

xhrObj.onreadystatechange = function() {

if ( xhrObj.readyState == 4 ) {

if ( bOrder ) {

EFWS.Script.queuedScripts[iQ].response = xhrObj.responseText;

EFWS.Script.injectScripts();

}

else {

eval(xhrObj.responseText);

if ( onload ) {

onload();

}

}

}

};

xhrObj.open('GET', url, true);

xhrObj.send('');

}

process queue (next slide) or... eval now, call callback save response to queue add to queue (if bOrder) 47. EFWS.injectScripts

// Process queued scripts to see if any are ready to inject.

injectScripts: function() {

var len = EFWS.Script.queuedScripts.length;

for ( var i = 0; i < len; i++ ) {

var qScript = EFWS.Script.queuedScripts[i];

if ( ! qScript.done ) {

if ( ! qScript.response ) {

// STOP! need to wait for this response

break;

}

else {

eval(qScript.response);

if ( qScript.onload ) {

qScript.onload();

}

qScript.done = true;

}

}

}

}

preserves external script order non-blocking works in all browsers couples with inlined code works with scripts across domains ready for this script, eval and call callback bail need to wait to preserve order if not yet injected 48. technique 2: DOM Element and Doc Write Firefox & Opera use Script DOM Element IE usedocument.writeScript Tag Safari, Chrome no benefit; rely on Safari 4 and Chrome 2 49. EFWS.loadScripts

loadScripts: function(aUrls, onload) {

// first pass: see if any of the scripts are on a different domain

var nUrls = aUrls.length;

var bDifferent = false;

for ( var i = 0; i < nUrls; i++ ) {

if ( EFWS.Script.differentDomain(aUrls[i]) ) {

bDifferent = true;

break;

}

}

// pick the best loading function

var loadFunc = EFWS.Script.loadScriptXhrInjection;

if ( bDifferent ) {

if ( -1 != navigator.userAgent.indexOf('Firefox') ||

-1 != navigator.userAgent.indexOf('Opera') ) {

loadFunc = EFWS.Script.loadScriptDomElement;

}

else {

loadFunc = EFWS.Script.loadScriptDocWrite;

}

}

// second pass: load the scripts

for ( var i = 0; i < nUrls; i++ ) {

loadFunc(aUrls[i], ( i+1 == nUrls ? onload : null ), true);

}

}

50. multiple scripts with dependencies

var aRaceConditions = [['couple-normal.php', 'Normal...];

var aWorkarounds = [['hardcoded-callback.php', 'Hardcod...];

var aMultipleScripts = [['managed-xhr.php', 'Managed XH...];

var aLoadScripts = [['loadscript.php', 'loadScript'], ...];

var aSubmenus = [["Race Conditions", aRaceConditions], ...];

function init() {

EFWS.Menu.createTieredMenu('examplesbtn', aSubmenus);

}

EFWS.Script.loadScripts(["menu.js", "menutier.js"], init);

scripts on same domain:

• order preserved, no blocking

scripts on different domain:

• order preserved: all

• loads scripts in parallel: all except Saf3, Chr1

• load script and image in parallel: FF, Saf4, Chr2

51. asynchronous scripts wrap-up 52. case study: Google Analytics

recommended pattern: 1

var gaJsHost = (("https:" == document.location.protocol) ? "https://ssl." : "http://www.");

document.write(unescape("%3Cscript src='" + gaJsHost + "google-analytics.com/ga.js' type='text/javascript'%3E%3C/script%3E"));

var pageTracker = _gat._getTracker("UA-xxxxxx-x");

pageTracker._trackPageview();

document.writeScript Tag approach blocks other resources

1 http://www.google.com/support/analytics/bin/answer.py?hl=en&answer=55488 53. case study: dojox.analytics.Urchin 1

_loadGA: function(){

var gaHost = ("https:" == document.location.protocol) ?

"https://ssl." : "http://www.";

dojo.create('script', {

src: gaHost + "google-analytics.com/ga.js"

}, dojo.doc.getElementsByTagName("head")[0]);

setTimeout(dojo.hitch(this, "_checkGA"), this.loadInterval);

},

_checkGA: function(){

setTimeout(dojo.hitch(this, !window["_gat"] ? "_checkGA" : "_gotGA"), this.loadInterval);

},

_gotGA: function(){

this.tracker = _gat._getTracker(this.acct); ...

}

Script DOM Element approach

"timer" coupling technique(script onload better)

1 http://docs.dojocampus.org/dojox/analytics/Urchin 54. 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

55. bad: stylesheet followed by inline script

browsers download stylesheets in parallel with other resources that follow...

...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

56. don't scatter inline scripts eBay MSN MySpace Wikipedia 57. iframes:most expensive DOM element

load 100emptyelements of each type

tested in all major browsers 1

1 IE 6, 7, 8; FF 2, 3.0, 3.1b2; Safari 3.2, 4; Opera 9.63, 10; Chrome 1.0, 2.0 58. iframes block onload

parent's onload doesn't fire until iframe and all its components are downloaded

workaround for Safari and Chrome: set iframe src in JavaScript

document.getElementById('iframe1').src=" url ";

59. scripts block iframe

no surprise scripts in the parent block the iframe from loading

IE Firefox Safari Chrome Opera script script script 60. stylesheets block iframe (IE, FF)

surprise stylesheets in the parent block the iframe or its resources in IE & Firefox

IE Firefox Safari Chrome Opera stylesheet stylesheet stylesheet 61. stylesheets after iframe still block (FF)

surprise even moving the stylesheetafterthe iframe still causes the iframe's resources to be blocked in Firefox

IE Firefox Safari Chrome Opera stylesheet stylesheet stylesheet 62. iframes: no free connections

iframe shares connection pool with parent (here 2 connections per server in IE 7)

iframe parent 63. flush 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:

• $|orFileHandle autoflush(Perl),flush(Python),ios.flush(Ruby)

call PHP'sflush() html image image script html image image script 64. flushing and domain blocking

you might need to move flushed resources to a domain different from the HTML doc

case study: Google search blocked by HTML document different domains html image image script html image image script google image image script image 204 65. takeaways

focus on the frontend

run YSlow:http://developer.yahoo.com/yslow

this year's focus: JavaScript

speed matters

66. impact on revenue

Google:

Yahoo:

Amazon:

1http://home.blarg.net/~glinden/StanfordDataMining.2006-11-29.ppt 2http://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 67. cost savings

hardware reduced load

bandwidth reduced response size

http://billwscott.com/share/presentations/2008/stanford/HPWP-RealWorld.pdf 68.

if you want

• better user experience

• more revenue

• reduced operating expenses

the strategy is clear

Even Faster Web Sites

69. Steve Souders [email_address] http://stevesouders.com/docs/sxsw-20090314.ppt