Faster Web Sites

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 iGoogle, empty cache Time Spent on the Frontend www.aol.com www.ebay.com www.facebook.com www.google.com/search search.live.com/results www.msn.com www.myspace.com en.wikipedia.org/wiki www.yahoo.com www.youtube.com Empty Cache 97% 95% 95% 47% 67% 98% 98% 94% 97% 98% Primed Cache 97% 81% 81% 0% 0% 94% 98% 91% 96% 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 1. Make fewer HTTP requests 2. Use a CDN 3. Add an Expires header 4. Gzip components 5. Put stylesheets at the top 6. Put scripts at the bottom 7. Avoid CSS expressions 8. Make JS and CSS external 9. Reduce DNS lookups 10. Minify JS 11. Avoid redirects 12. Remove duplicate scripts 13. Configure ETags 14. Make AJAX cacheable YSlow High Performance Web Sites http://conferences.oreilly.com/velocity/ 20% discount: vel08st Even Faster Web Sites 1. Split the initial payload 2. Load scripts without blocking 3. Don't scatter scripts 4. Split dominant content domains 5. Make static content cookie-free 6. Reduce cookie weight 7. Minify CSS 8. Optimize images 9. Use iframes sparingly 10.To www or not to www Why focus on JavaScript? Yahoo! Wikipedia eBay AOL MySpace YouTube Facebook Scripts Block 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("" + ""); 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 Browser Busy Indicators status bar progress bar logo cursor block render block onload normal Script Src XHR Eval XHR Injection Script in Iframe Script DOM Element Script Defer document.write Script Tag FF no no IE,FF FF IE,FF no no FF FF IE,FF no no IE,FF FF FF no no FF FF IE,FF no no no no IE,FF no no IE,FF FF FF FF FF IE,FF FF IE,FF FF FF FF IE,FF IE,FF IE,FF 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 || domains existing browser ensures downcan scripts busy order loads differ size (bytes) normal Script Src XHR Eval XHR Injection Script in Iframe Script DOM Element Script Defer document.write Script Tag no IE,FF IE,FF IE,FF IE,FF IE IE* yes no no no yes yes yes yes no yes no yes yes yes IE,FF no no IE,FF FF IE,FF IE,FF IE,FF no no no FF IE IE ~50 ~500 ~500 ~50 ~200 ~50 ~100 *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 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/