Even Faster Web Sites
best practices for faster pages
Steve Souders
souders@google.com
http://stevesouders.com/docs/linkedin-20080805.ppt
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 Empty Cache 97% Primed Cache 97%
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
95% 95% 47% 67% 98% 98% 94% 97% 98%
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/
June 22-24, 2009
High Performance Web Sites, Vol 2
1. Split the initial payload 2. Load scripts without blocking 3. Don't scatter inline scripts 4. Split dominant 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
blocks parallel downloads and rendering
http://stevesouders.com/cuzillion/?ex=10008
What's "Cuzillion"?
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/
Initial Payload and Execution
JavaScript Functions Executed before onload
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
115K 183K 1088K 15K 17K 131K 297K 114K 321K 240K 252K avg
30% 44% 9% 45% 24% 31% 18% 32% 13% 18% 26% avg
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?
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)
Advanced Script Loading
XHR Eval
XHR Injection
Script in Iframe Script DOM Element Script Defer document.write Script Tag
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
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
Script in 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
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
Script Defer
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 FF FF
IE,FF
no no FF FF FF IE,FF
IE,FF
no no IE,FF FF FF IE,FF
FF
no no FF FF FF FF
IE,FF
no no no no FF IE,FF
IE,FF
no no IE,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 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
long executing inline scripts block rendering and downloads
http://stevesouders.com/cuzillion/?ex=10035
workarounds:
initiate execution with setTimeout (>250 for FF, nglayout.initialpaint.delay) move JavaScript to external script with advanced downloading techniques use Defer attribute (IE only)
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 use Link, not @import
Examples of Scattered Scripts
MSN Wikipedia eBay MySpace
Don't Scatter Inline 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
this year's focus: JavaScript
Split the Initial Payload Load Scripts without Blocking Don't Scatter Inline Scripts
speed matters
you CAN make your site even faster!
Announcement 1: HTTPWatch for FF
http://httpwatch.com/ previously IE only Firefox private beta now
Firebug 1.05 Net Panel buggy
Announcement 2: Firebug Lite 1.2
http://getfirebug.com/lite.html console.log Inspect
DOM and CSS
Announcement 3: Mozilla & Firebug
John Resig, Rob Campbell, Jan Odvarko Firebug Working Group stability, performance, bug fixes
LinkedIn Analysis
1
2 3
1. reduce backend time (25%) 2. raise inline script after stylesheet var google_keywords = 'Internet', ...; 5. ads – where to begin?! prod/css?f=css..."> var google_keywords = 'Internet', ...; 6. lazy load scripts 4
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Steve Souders
souders@google.com
http://stevesouders.com/docs/linkedin-20080805.ppt