Even Faster Web Sites at The Ajax Experience

the importance of frontend performance 17% 83% iGoogle, primed cache 9% 91% iGoogle, empty cache

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

web performance guy

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

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

scripts block <script src="A.js"> blocks parallel downloads and rendering 7 secs: IE 8, FF 3.5, Chr 2, Saf 4 9 secs: IE 6-7, FF 3.0, Chr 1, Op 9-10, Saf 3

MSN.com: parallel scripts 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

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

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('');

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

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');

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

Script Defer <script defer src='A.js'></script> supported in IE and FF 3.1+ script and main page domains can differ no need to refactor JavaScript

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.write s must be in same script block

browser busy indicators

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

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

menu.js image.gif

asynchronous JS example: menu.js

<script type="text/javascript">

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>

script DOM element approach

before after menu.js image.gif menu.js image.gif

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

what about

inlined code

that depends on the script?

coupling techniques

hardcoded callback

window onload

timer

degrading script tags

script onload

technique 1: hardcoded callback

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

function init() {

}

</script>

init() is called from within menu.js

not very flexible

doesn't work for 3 rd party scripts

technique 2: window onload

<iframe src="menu.php" width=0 height=0 frameborder=0> </iframe>

function init() {

}

if ( window.addEventListener ) {

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

}

else if ( window.attachEvent ) {

window.attachEvent("onload", init);

}

</script>

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

technique 3: timer

function init() {

}

function initTimer(interval) {

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

setTimeout(initTimer, interval);

}

else {

init();

}

}

initTimer(300);

</script>

load if interval too low, delay if too high

slight increased maintenance – EFWS

John Resig's degrading script tags

<script src="menu-degrading.js" type="text/javascript">

function init() {

}

init();

</script>

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

technique 4: degrading script tags

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

function init() {

}

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

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

domscript.innerHTML = "init();";

}

else {

domscript.text = "init();";

}

</script>

elegant, flexible (cool!)

not well known

doesn't work for 3 rd party scripts (unless...)

technique 5: script onload

function init() {

}

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;

}

}

</script>

pretty nice, medium complexity

menu.js image.gif

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

multiple script example: menutier.js

<script src="menu.js" type="text/javascript"></script>

<script src="menutier.js" type="text/javascript"></script>

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);

}

</script>

technique 1: managed XHR

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

function init() {

}

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

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

</script>

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

before after

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)

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

technique 2: DOM Element and Doc Write Firefox & Opera – use Script DOM Element IE – use document.write Script Tag Safari, Chrome – no benefit; rely on Safari 4 and Chrome 2

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);

}

}

multiple scripts with dependencies

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

function init() {

}

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

</script>

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

asynchronous scripts wrap-up

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"));

</script>

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

pageTracker._trackPageview();

</script>

document.write Script Tag approach blocks other resources

1 http://www.google.com/support/analytics/bin/answer.py?hl=en&answer=55488

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

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!

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 FileHandle autoflush (Perl), flush (Python), ios.flush (Ruby)

call PHP's flush() html image image script html image image script

flushing and domain blocking

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

blocked by HTML document different domains html image image script html image image script

successful flushing

Google Search

external resource downloaded early

content visible to the user

http://www.google.com/images/nav_logo4.png google image image script image 204

performance analyzers (HPWS) YSlow Page Speed Pagetest VRTA neXpert combine JS & CSS X X X use CSS sprites X X use a CDN X X set Expires in the future X X X X X gzip text responses X X X X X put CSS at the top X X put JS at the bottom X avoid CSS expressions X X make JS & CSS external reduce DNS lookups X X minify JS X X X avoid redirects X X X X remove dupe scripts X remove ETags X X X

performance analyzers (EFWS) YSlow Page Speed Pagetest VRTA neXpert don't block UI thread split JS payload X load scripts async X inline JS b4 stylesheet X write efficient JS min. uncompressed size optimize images X X shard domains X X flush the document avoid iframes simplify CSS selectors X X

performance analyzers (other) YSlow Page Speed Pagetest VRTA neXpert use persistent conns X X X reduce cookies 2.0 X X X avoid net congestion X increase MTU, TCP win X avoid server congestion X remove unused CSS X specify image dims X use GET for Ajax 2.0 reduce DOM elements 2.0 avoid 404 errors 2.0 avoid Alpha filters 2.0 don't scale images 2.0 X optimize favicon 2.0

focus on the frontend

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

and Page Speed! ( http://code.google.com/speed/page-speed/ )

speed matters

takeaways

Bing:

Yahoo:

Google:

AOL:

Shopzilla:

impact on revenue 1 http://en.oreilly.com/velocity2009/public/schedule/detail/8523 2 http://www.slideshare.net/stoyan/yslow-20-presentation 3 http://en.oreilly.com/velocity2009/public/schedule/detail/7579 4 http://en.oreilly.com/velocity2009/public/schedule/detail/7709 +2000 ms  -4.3% revenue/user 1 +400 ms  -5-9% full-page traffic 2 +400 ms  -0.59% searches/user 1 fastest users  +50% page views 3 -5000 ms  +7-12% revenue 4