Even Faster Web Sites best practices for faster
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% 17% 91% 83% i. Google, primed cache i. Google, empty cache
Time Spent on the Frontend www. aol. com www. ebay. com www. facebook. com www. google. com/search. live. com/results www. msn. com www. myspace. com en. wikipedia. org/wiki www. yahoo. com www. youtube. com Empty Cache 97% 95% Primed Cache 97% 81% 47% 67% 98% 94% 97% 98% 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: vel 08 st
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 Java. Script? Yahoo! Wikipedia e. Bay AOL My. Space You. Tube Facebook
Scripts Block <script src="A. js"> blocks parallel downloads and rendering http: //stevesouders. com/cuzillion/? ex=10008 What's "Cuzillion"?
Cuzillion 'cuz there 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, 550 K uncompressed 9% of functionality is used before onload
Unexecuted Payload www. aol. com www. ebay. com www. facebook. com www. google. com/search. live. com/results www. msn. com www. myspace. com en. wikipedia. org/wiki www. yahoo. com www. youtube. com functions not used before onload 70% 56% 91% 55% 76% 69% 82% 68% 87% 82% 73. 6% avg
Split the initial payload split your Java. Script 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?
MSN. com: Parallel Scripts MSN Scripts and other resources downloaded in parallel! How? var p=g. get. Elements. By. Tag. Name("HEAD")[0]; var c=g. create. Element("script"); c. type="text/javascript"; c. onreadystatechange=n; c. onerror=c. onload=k; c. src=e; p. append. Child(c)
Advanced Script Loading XHR Eval XHR Injection Script in Iframe Script DOM Element Script Defer document. write Script Tag
XHR Eval var xhr. Obj = get. XHRObject(); xhr. Obj. onreadystatechange = function() { if ( xhr. Obj. ready. State != 4 ) return; eval(xhr. Obj. response. Text); }; xhr. Obj. open('GET', 'A. js', true); xhr. Obj. send(''); script must have same domain as main page must refactor script http: //stevesouders. com/cuzillion/? ex=10009
XHR Injection var xhr. Obj = get. XHRObject(); xhr. Obj. onreadystatechange = function() { if ( xhr. Obj. ready. State != 4 ) return; var se=document. create. Element('script'); document. get. Elements. By. Tag. Name('head') [0]. append. Child(se); se. text = xhr. Obj. response. Text; }; xhr. Obj. open('GET', 'A. js', true); xhr. Obj. 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=frame 1></iframe> iframe must have same domain as main page must refactor script: // access iframe from main page window. frames[0]. create. New. Div(); // access main page from iframe parent. document. create. Element('div'); http: //stevesouders. com/cuzillion/? ex=10012
Script DOM Element var se = document. create. Element('script'); se. src = 'http: //anydomain. com/A. js'; document. get. Elements. By. Tag. Name('head') [0]. append. Child(se); script and main page domains can differ no need to refactor Java. Script 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 Java. Script http: //stevesouders. com/cuzillion/? ex=10013
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
Browser Busy Indicators
Browser Busy Indicators normal Script Src XHR Eval XHR Injection Script in Iframe Script DOM Element Script Defer document. write Script Tag status bar progress bar logo cursor block render block onload FF IE, FF no no no IE, FF FF no IE, FF FF FF no FF FF 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 normal Script Src size (bytes) no yes IE, FF ~50 XHR Eval XHR Injection Script in Iframe Script DOM Element IE, FF no no ~500 IE, FF no yes no no ~500 IE, FF no no IE, FF no ~50 IE, FF yes FF FF ~200 Script Defer document. write Script Tag IE yes IE, FF IE ~50 IE* yes IE, FF IE ~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 set. Timeout move Java. Script 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 e. Bay My. Space
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: Java. Script 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/
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