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Web 2.0 Expo: Even Faster Web Sites
- 1. 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.
- 2. The Importance of Frontend Performance 17% 83% iGoogle, primed cache 9% 91% iGoogle, empty cache
- 3. 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%
- 4. 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
- 5. 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
- 6. High Performance Web Sites YSlow
- 7. http://conferences.oreilly.com/velocity/ 20% discount: vel08st
- 8. 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
- 9. Why focus on JavaScript? AOL eBay Facebook MySpace Wikipedia Yahoo! YouTube
- 10. Scripts Block <script src=&quot;A.js&quot;> blocks parallel downloads and rendering What's &quot;Cuzillion&quot;? http://stevesouders.com/cuzillion/?ex=10008
- 11. 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/
- 12. Split the Initial Payload: Facebook 43 external scripts, 550K uncompressed 9% of functionality is used before onload
- 13. 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%
- 14. 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?
- 15. 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
- 16. Advanced Script Loading XHR Eval XHR Injection Script in Iframe Script DOM Element Script Defer document.write Script Tag
- 17. 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
- 18. 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
- 19. 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
- 20. 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
- 21. 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
- 22. 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
- 24. Browser Busy Indicators good to show busy indicators when the user needs feedback bad when downloading in the background
- 25. 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
- 26. Summary of Traits * Only other document.write scripts are downloaded in parallel (in the same script block).
- 27. and the winner is...
- 28. 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?
- 29. 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
- 30. 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
- 31. Examples of Scattered Scripts eBay MSN MySpace Wikipedia
- 32. 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
- 33. 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!
- 34. Steve Souders [email_address] http://stevesouders.com/
Editor's Notes
- Permission to use photo given by Amnemona: http://www.flickr.com/photos/marinacvinhal/379111290/