SXSW: Even Faster Web Sites

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.

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

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%

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

25% discount code: "ssouders25"

Sept 2007

June 2009

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)

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

scripts block <script src="A.js"> blocks parallel downloads and rendering http://stevesouders.com/cuzillion/?ex=10008

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

asynchronous script loading 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(''); http://stevesouders.com/cuzillion/?ex=10009

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

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

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

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

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.write s must be in same script block http://stevesouders.com/cuzillion/?ex=10014

browser busy indicators

browser busy indicators good to show busy indicators when the user needs feedback bad when downloading in the background

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

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

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?

synchronous JS example: menu.js

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

<script type="text/javascript">

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>

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() {

}

init();

</script>

script DOM element approach

before after

load scripts without blocking * Only other document.write scripts are downloaded in parallel (in the same script block). !IE

asynchronous scripts wrap-up

what about

inlined code

that depends on the script?

what about

inlined code

that depends on the script?

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

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

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

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

best to move inline scripts above stylesheets or below other resources

use Link, not @import

don't scatter inline scripts eBay MSN MySpace Wikipedia

iframes: most expensive DOM element

load 100 empty elements 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

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

<iframe id=iframe1 src=""></iframe>

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

</script>

scripts block iframe

no surprise – scripts in the parent block the iframe from loading

IE Firefox Safari Chrome Opera script script script

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

stylesheets after iframe still block (FF)

surprise – even moving the stylesheet after the iframe still causes the iframe's resources to be blocked in Firefox

IE Firefox Safari Chrome Opera stylesheet stylesheet stylesheet

iframes: no free connections

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

iframe parent

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:

$| 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

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

takeaways

focus on the frontend

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

this year's focus: JavaScript

speed matters

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

cost savings