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Web 2.0 Expo: Even Faster Web Sites


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Web 2.0 Expo: Even Faster Web Sites

  1. Steve Souders [email_address] 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 97% 97% 95% 81% 95% 81% 47% 0% 67% 0% 98% 94% 98% 98% 94% 91% 97% 96% 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 <ul><li>Make fewer HTTP requests </li></ul><ul><li>Use a CDN </li></ul><ul><li>Add an Expires header </li></ul><ul><li>Gzip components </li></ul><ul><li>Put stylesheets at the top </li></ul><ul><li>Put scripts at the bottom </li></ul><ul><li>Avoid CSS expressions </li></ul><ul><li>Make JS and CSS external </li></ul><ul><li>Reduce DNS lookups </li></ul><ul><li>Minify JS </li></ul><ul><li>Avoid redirects </li></ul><ul><li>Remove duplicate scripts </li></ul><ul><li>Configure ETags </li></ul><ul><li>Make AJAX cacheable </li></ul>
  6. High Performance Web Sites YSlow
  7. <ul><li> 20% discount: vel08st </li></ul>
  8. Even Faster Web Sites <ul><li>Split the initial payload </li></ul><ul><li>Load scripts without blocking </li></ul><ul><li>Don't scatter scripts </li></ul><ul><li>Split dominant content domains </li></ul><ul><li>Make static content cookie-free </li></ul><ul><li>Reduce cookie weight </li></ul><ul><li>Minify CSS </li></ul><ul><li>Optimize images </li></ul><ul><li>Use iframes sparingly </li></ul><ul><li>To www or not to www </li></ul>
  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;?
  11. Cuzillion 'cuz there are a zillion pages to check a tool for quickly constructing web pages to see how components interact Open Source
  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 70% 56% 91% 55% 76% 69% 82% 68% 87% 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. 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); };'GET', 'A.js', true); xhrObj.send('');
  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; };'GET', 'A.js', true); xhrObj.send(''); script must have same domain as main page
  19. Script in Iframe <iframe src='A.html' width=0 height=0 frameborder=0 id=frame1></iframe> <ul><li>iframe must have same domain as main page </li></ul><ul><li>must refactor script: </li></ul><ul><ul><li>// access iframe from main page </li></ul></ul><ul><ul><li>window.frames[0].createNewDiv(); </li></ul></ul><ul><ul><li>// access main page from iframe </li></ul></ul><ul><ul><li>parent.document.createElement('div'); </li></ul></ul>
  20. Script DOM Element var se = document.createElement('script'); se.src = ''; document.getElementsByTagName('head') [0].appendChild(se); script and main page domains can differ no need to refactor JavaScript
  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
  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
  23. Browser Busy Indicators
  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 <ul><li>Ensure scripts execute in order: </li></ul><ul><ul><li>necessary when scripts have dependencies </li></ul></ul><ul><ul><li>IE: </li></ul></ul><ul><ul><li>FF: </li></ul></ul><ul><li>Avoid scripts executing in order: </li></ul><ul><ul><li>faster – first script back is executed immediately </li></ul></ul><ul><ul><li> </li></ul></ul>
  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 <ul><li>don't let scripts block other downloads </li></ul><ul><li>you can still control execution order, busy indicators, and onload event </li></ul><ul><li>What about inline scripts? </li></ul>
  29. Inline Scripts Block Rendering <ul><li>long executing inline scripts block rendering of the entire page </li></ul><ul><li> </li></ul><ul><li>workarounds: </li></ul><ul><ul><li>initiate execution with setTimeout </li></ul></ul><ul><ul><li>move JavaScript to external script with advanced downloading techniques </li></ul></ul>
  30. Inline Scripts after Stylesheets Block Downloading <ul><li>Firefox blocks parallel downloads when downloading stylesheets </li></ul><ul><li>IE doesn't... </li></ul><ul><li>...unless the stylesheet is followed by an inline script </li></ul><ul><li> </li></ul><ul><li>best to move inline scripts above stylesheets or below other resources </li></ul>
  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 <ul><li>focus on the frontend </li></ul><ul><li>run YSlow: </li></ul><ul><li>Velocity: register before May 5 </li></ul><ul><li>this year's focus: JavaScript </li></ul><ul><ul><li>Split the Initial Payload </li></ul></ul><ul><ul><li>Load Scripts without Blocking </li></ul></ul><ul><ul><li>Don't Scatter Scripts </li></ul></ul><ul><li>speed matters </li></ul><ul><li>you CAN make your site even faster! </li></ul>
  34. Steve Souders [email_address]