even faster web sites

17%

83%

iGoogle, primed cache

the importance of frontend performance

9% 91%

iGoogle, empty cache

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

Sept 2007

June 2009

Even Faster Web SitesSplitting the initial payloadLoading scripts without blockingCoupling asynchronous scriptsPositioning inline scriptsSharding dominant domainsFlushing the document earlyUsing iframes sparinglySimplifying CSS Selectors

Understanding Ajax performance..........Doug CrockfordCreating responsive web apps............Ben Galbraith, Dion

AlmaerWriting efficient JavaScript.............Nicholas ZakasScaling with Comet.....................Dylan SchiemannGoing beyond gzipping...............Tony GentilcoreOptimizing images...................Stoyan Stefanov, Nicole

Sullivan

AOLeBayFacebookMySpaceWikipediaYahoo!

Why focus on JavaScript?

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

JavaScript

Functions Executed before

onload

www.aol.com 115K 30%

www.ebay.com 183K 44%

www.facebook.com 1088K 9%

www.google.com/search

15K 45%

search.live.com/results

17K 24%

www.msn.com 131K 31%

www.myspace.com 297K 18%

en.wikipedia.org/wiki 114K 32%

www.yahoo.com 321K 13%

www.youtube.com 240K 18%

26% avg252K avg

initial payload and execution

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?

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

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 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 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 pagewindow.frames[0].createNewDiv();

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

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

<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

Script Defer

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

document.write Script Tag

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

Load Scripts Without Blocking

XHR EvalXHR InjectionScript in iframeScript DOM ElementScript Defer

Script DOM ElementScript Defer

Script DOM Element

Script DOM Element (FF)Script Defer (IE)

XHR EvalXHR InjectionScript in iframeScript DOM Element (IE)

XHR InjectionXHR EvalScript DOM Element (IE)

Managed XHR InjectionManaged XHR EvalScript DOM Element

Managed XHR InjectionManaged XHR Eval

Script DOM Element (FF)Script Defer (IE)Managed XHR EvalManaged XHR Injection

Script DOM Element (FF)Script Defer (IE)Managed XHR EvalManaged XHR Injection

different domains same domains

no order

preserve order

no order

no busyshow busy

show busyno busy

preserve order

and the winner is...

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

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

!IE

Loading Scripts Without Blocking

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

asynchronous loading & coupling

async technique: Script DOM Elementeasy, cross-browserdoesn't ensure script order

coupling technique: script onloadfairly easy, cross-browserensures 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!

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:

1 http://en.oreilly.com/velocity2009/public/schedule/detail/8523 2 http://www.slideshare.net/stoyan/yslow-20-presentation3 http://en.oreilly.com/velocity2009/public/schedule/detail/75794 http://en.oreilly.com/velocity2009/public/schedule/detail/7709

+2000 ms -4.3% revenue/user1

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

+400 ms -0.59% searches/user1

fastest users +50% page views3

-5000 ms +7-12% revenue4

impact on revenue

hardware – reduced loadShopzilla – 50% fewer servers

bandwidth – reduced response size

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

cost savings

if you want better user experience more revenue reduced operating costs

the strategy is clear

Even Faster Web Sites

Steve Souderssouders@google.com

http://stevesouders.com/docs/jquery-20090913.ppt

book signing now