Web 2.0 Expo: Even Faster Web Sites

Steve Souders [email_address] http://stevesouders.com/ Even Faster Web Sites best practices for faster pages 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 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 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

High Performance Web Sites YSlow

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

Even Faster Web Sites

Split the initial payload

Load scripts without blocking

Don't scatter scripts

Split dominant content domains

Make static content cookie-free

Reduce cookie weight

Minify CSS

Optimize images

Use iframes sparingly

To www or not to www

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

Scripts Block <script src="A.js"> blocks parallel downloads and rendering What's "Cuzillion"? http://stevesouders.com/cuzillion/?ex=10008

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 73.6% avg functions not used before onload www.aol.com 70% www.ebay.com 56% www.facebook.com 91% www.google.com/search 55% search.live.com/results 76% www.msn.com 69% www.myspace.com 82% en.wikipedia.org/wiki 68% www.yahoo.com 87% www.youtube.com 82%

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 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) MSN

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 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.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

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 Rendering

long executing inline scripts block rendering of the entire page

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

best to move inline scripts above stylesheets or below other resources

Examples of Scattered Scripts eBay MSN MySpace Wikipedia

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