Web 2.0 Expo: Even Faster Web Sites

Slide 1: 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.

Slide 2: The Importance of Frontend Performance 9% 91% 17% 83% iGoogle, primed cache iGoogle, empty cache

Slide 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%

Slide 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

Slide 5: 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

Slide 6: YSlow High Performance Web Sites

Slide 7: http://conferences.oreilly.com/velocity/ 20% discount: vel08st

Slide 8: 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

Slide 9: Why focus on JavaScript? Yahoo! Wikipedia eBay AOL MySpace YouTube Facebook

Slide 10: Scripts Block <script src="A.js"> blocks parallel downloads and rendering http://stevesouders.com/cuzillion/?ex=10008 What's "Cuzillion"?

Slide 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/

Slide 12: Split the Initial Payload: Facebook 43 external scripts, 550K uncompressed 9% of functionality is used before onload

Slide 13: Unexecuted Payload 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% 73.6% avg

Slide 14: 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?

Slide 15: 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)

Slide 16: Advanced Script Loading XHR Eval XHR Injection Script in Iframe Script DOM Element Script Defer document.write Script Tag

Slide 17: XHR Eval var xhrObj = 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

Slide 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

Slide 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

Slide 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

Slide 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

Slide 22: 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

Slide 23: Browser Busy Indicators

Slide 24: Browser Busy Indicators good to show busy indicators when the user needs feedback bad when downloading in the background

Slide 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

Slide 26: Summary of Traits Only other document.write scripts are downloaded in parallel (in the same script block). *

Slide 27: and the winner is...

Slide 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?

Slide 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 s etTimeout move JavaScript to external script with advanced downloading techniques

Slide 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

Slide 31: Examples of Scattered Scripts MSN Wikipedia eBay MySpace

Slide 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

Slide 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!

Slide 34: Steve Souders souders@google.com http://stevesouders.com/