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Web20expo 20080425

The document discusses techniques for improving frontend web performance, including splitting code into critical and non-critical sections, loading scripts asynchronously without blocking other downloads, and avoiding scattering scripts throughout a page. It provides examples of sites that could benefit from these techniques and recommends tools like YSlow for auditing performance. The overall message is that frontend optimizations like JavaScript improvements can significantly speed up sites.

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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=&quot;A.js&quot;> blocks parallel downloads and rendering What's &quot;Cuzillion&quot;? 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 &quot;everything else&quot; 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(&quot;HEAD&quot;)[0]; var c=g.createElement(&quot;script&quot;); c.type=&quot;text/javascript&quot;; 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 (&quot;<scri&quot; + &quot;ipt type='text/javascript' src='A.js'>&quot; + &quot;</scri&quot; + &quot;ipt>&quot;); 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 http://stevesouders.com/cuzillion/? ex=10019
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 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 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 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 [email_address] http://stevesouders.com/