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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.
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Even Faster Web Sitesbest 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
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
YSlow High Performance Web Sites
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? 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 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 varxhrObj = 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 varxhrObj = 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 defersrc='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 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 *Only other document.write scripts are downloaded in parallel (in the same script block).
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/