Steve Souderssouders@google.com

http://stevesouders.com/docs/sxsw-20090314.ppt

Even Faster Web Sites

Disclaimer: This content does not necessarily reflect the opinions of my employer.

17%

83%

iGoogle, primed cache

the importance of frontend performance

9% 91%

iGoogle, empty cache

time spent on the frontend

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%April 2008

14 RULES

1. MAKE FEWER HTTP REQUESTS

2. USE A CDN3. ADD AN EXPIRES HEADER4. GZIP COMPONENTS5. PUT STYLESHEETS AT THE

TOP6. PUT SCRIPTS AT THE

BOTTOM7. AVOID CSS EXPRESSIONS8. MAKE JS AND CSS

EXTERNAL9. REDUCE DNS LOOKUPS10.MINIFY JS11.AVOID REDIRECTS12.REMOVE DUPLICATE

SCRIPTS13.CONFIGURE ETAGS14.MAKE AJAX CACHEABLE

25% discount code: "ssouders25"

Sept 2007

June 2009

Even Faster Websites

Split the initial payloadLoad scripts without

blockingCouple asynchronous scripts

Don't scatter inline scriptsSplit the dominant

domainFlush 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)

AOLeBayFacebookMySpaceWikipediaYahoo!

why focus on JavaScript?

YouTube

scripts block

<script src="A.js"> blocks parallel downloads and rendering

http://stevesouders.com/cuzillion/?ex=10008

MSNScripts 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

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 Injectionvar 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 pagehttp://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 pagewindow.frames[0].createNewDiv();

// access main page from iframeparent.document.createElement('div');

http://stevesouders.com/cuzillion/?ex=10012

Script DOM Elementvar 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 Tagdocument.write("<scr" + "ipt type='text/javascript' src='A.js'>" + "</scr" + "ipt>");

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

load scripts without blocking

*Only other document.write scripts are downloaded in parallel (in the same script block).

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

load 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 5: script onload<script type="text/javascript">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);</script>

pretty nice, medium complexity

case study: Google Analytics

recommended pattern:1

<script type="text/javascript">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>

<script type="text/javascript">var pageTracker = _gat._getTracker("UA-xxxxxx-x");pageTracker._trackPageview();</script>

document.write Script Tag approach blocks other resources

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

case study: dojox.analytics.Urchin1

_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)1http://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

http://stevesouders.com/cuzillion/?ex=10021

best to move inline scripts above stylesheets or below other resources

use Link, not @import

eBayMSNMySpaceWikipedia

don't scatter inline scripts

iframes: most expensive DOM element

load 100 empty elements of each type

tested in all major browsers1

1IE 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><script type="text/javascript">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)

htmlimageimagescript

htmlimageimagescript call PHP's flush()

flushing and domain blocking

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

imageimagescript

htmlimageimagescript

googleimageimagescriptimage204

case study: Google search

blocked by HTML document

different domains

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.ppt2 http://www.slideshare.net/stoyan/yslow-20-presentation

+500 ms -20% traffic1

+400 ms -5-9% full-page traffic2

+100 ms -1% sales1

cost savings

hardware – reduced load

bandwidth – reduced response size

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

if you want better user experience more revenue reduced operating expenses

the strategy is clear

Even Faster Web Sites

Steve Souderssouders@google.com

http://stevesouders.com/docs/sxsw-20090314.ppt