steve souders souders@google.com even faster web sites best practices for faster pages disclaimer:...

Steve Souderssouders@google.comhttp://stevesouders.com/

Even Faster Web Sites best practices for faster pages

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%

The Performance Golden Rule

80-90% of the end-user response time is spent on the frontend. Start there.

greater potential for improvement

simpler

proven to work

14 Rules1. Make fewer HTTP

requests2. 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

High Performance Web Sites

YSlow

http://conferences.oreilly.com/velocity/ 20% discount: vel08st

High Performance Web Sites, Vol 2

1. Split the initial payload2. Load scripts without blocking3. Don't scatter inline scripts4. Split dominant domains5. Make static content cookie-free6. Reduce cookie weight7. Minify CSS8. Optimize images9. Use iframes sparingly10.To www or not to www

AOLeBayFacebookMySpaceWikipediaYahoo!

Why focus on JavaScript?

YouTube

Scripts Block

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

What's "Cuzillion"?

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

a tool for quickly constructing web pages to see how components interact

Open Source

http://stevesouders.com/cuzillion/

Cuzillion'cuz there are a zillion pages to check

Initial Payload and Execution

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

Split 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?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

Advanced 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

script and main page domains can differ

no need to refactor JavaScript

http://stevesouders.com/cuzillion/?ex=10013

document.write Script Tagdocument.write("<scri" + "ipt type='text/javascript' src='A.js'>" + "</scri" + "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

Browser Busy Indicators

Browser Busy Indicators

good to show busy indicators when the user needs feedback

bad when downloading in the background

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

immediatelyhttp://stevesouders.com/cuzillion/?ex=10019

Ensure/Avoid Ordered Execution

Summary of Traits

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

and the winner is...

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?

Inline Scripts Block

long executing inline scripts block rendering and downloads

http://stevesouders.com/cuzillion/?ex=10035

workarounds: initiate execution with setTimeout (>250

for FF, nglayout.initialpaint.delay)move JavaScript to external script with

advanced downloading techniquesuse Defer attribute (IE only)

Inline Scripts after Stylesheets Block Downloading

Firefox blocks parallel downloads when downloading stylesheets

IE doesn't...

...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

Examples of Scattered Scripts

Don't Scatter Inline Scripts

remember inline scripts carry a cost

avoid long-executing inline scripts

don't put inline scripts between stylesheets and other resources

Takeaways

focus on the frontend

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

this year's focus: JavaScriptSplit the Initial PayloadLoad Scripts without BlockingDon't Scatter Inline Scripts

speed matters

you CAN make your site even faster!

Steve Souderssouders@google.comhttp://stevesouders.com/