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Faster Web Sites Powered By Docstoc
					Even Faster Web Sites
best practices for faster pages

Steve Souders
souders@google.com
http://stevesouders.com/
Disclaimer: This content does not necessarily reflect the opinions of my employer.

The Importance of Frontend Performance
9% 91%

17%

83%

iGoogle, primed cache

iGoogle, empty cache

Time Spent on the Frontend
www.aol.com www.ebay.com www.facebook.com www.google.com/search search.live.com/results www.msn.com www.myspace.com en.wikipedia.org/wiki www.yahoo.com www.youtube.com Empty Cache 97% 95% 95% 47% 67% 98% 98% 94% 97% 98% Primed Cache 97% 81% 81% 0% 0% 94% 98% 91% 96% 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 Rules
1. Make fewer HTTP requests 2. Use a CDN 3. Add an Expires header 4. Gzip components 5. Put stylesheets at the top 6. Put scripts at the bottom 7. Avoid CSS expressions 8. Make JS and CSS external 9. Reduce DNS lookups 10. Minify JS 11. Avoid redirects 12. Remove duplicate scripts 13. Configure ETags 14. Make AJAX cacheable

YSlow

High Performance Web Sites

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

Even Faster Web Sites
1. Split the initial payload 2. Load scripts without blocking 3. Don't scatter scripts 4. Split dominant content domains 5. Make static content cookie-free 6. Reduce cookie weight 7. Minify CSS 8. Optimize images 9. Use iframes sparingly 10.To www or not to www

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

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

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

What's "Cuzillion"?

Cuzillion
'cuz there are a zillion pages to check

a tool for quickly constructing web pages to see how components interact Open Source http://stevesouders.com/cuzillion/

Split the Initial Payload: Facebook

43 external scripts, 550K uncompressed 9% of functionality is used before onload

Unexecuted Payload
www.aol.com www.ebay.com www.facebook.com www.google.com/search search.live.com/results www.msn.com www.myspace.com en.wikipedia.org/wiki www.yahoo.com www.youtube.com

functions not used before onload 70% 56% 91% 55% 76% 69% 82% 68% 87% 82% 73.6% 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?

MSN.com: Parallel Scripts
MSN
Scripts 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)

Advanced Script Loading
XHR Eval XHR Injection

Script in Iframe Script DOM Element Script Defer document.write Script Tag

XHR Eval
var xhrObj = getXHRObject(); xhrObj.onreadystatechange = function() { if ( xhrObj.readyState != 4 ) return; eval(xhrObj.responseText); }; xhrObj.open('GET', 'A.js', true); xhrObj.send('');

script must have same domain as main page must refactor script
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 script and main page domains can differ no need to refactor JavaScript

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

document.write Script Tag
document.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
status bar progress bar logo cursor block render block onload

normal Script Src XHR Eval XHR Injection Script in Iframe Script DOM Element Script Defer document.write Script Tag

FF no no IE,FF FF

IE,FF no no FF FF

IE,FF no no IE,FF FF

FF no no FF FF

IE,FF no no no no

IE,FF no no IE,FF FF

FF
FF

FF
IE,FF

FF
IE,FF

FF
FF

FF
IE,FF

IE,FF
IE,FF

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

Summary of Traits
|| domains existing browser ensures downcan scripts busy order loads differ

size (bytes)

normal Script Src XHR Eval XHR Injection Script in Iframe Script DOM Element Script Defer document.write Script Tag

no IE,FF IE,FF IE,FF IE,FF IE IE*

yes no no no yes yes yes

yes no yes no yes yes yes

IE,FF no no IE,FF FF IE,FF IE,FF

IE,FF no no no FF IE IE

~50 ~500 ~500 ~50 ~200 ~50 ~100

*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 Rendering
long executing inline scripts block rendering of the entire page
http://stevesouders.com/cuzillion/?ex=10020

workarounds:
initiate execution with setTimeout move JavaScript to external script with advanced downloading techniques

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

Examples of Scattered Scripts
MSN Wikipedia eBay MySpace

Don't Scatter 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 Velocity: register before May 5 this year's focus: JavaScript
Split the Initial Payload Load Scripts without Blocking Don't Scatter Scripts

speed matters you CAN make your site even faster!

Steve Souders
souders@google.com
http://stevesouders.com/


				
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posted:5/1/2008
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Description: Even faster web sites - best practices for faster pages