steve souders [email protected] life's too short, write fast code part 1 disclaimer: this...
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Steve [email protected]
http://stevesouders.com/docs/facebook-20081030.ppt
Life's too short,write fast code
part 1
Disclaimer: This content does not necessarily reflect the opinions of my employer.
17%
83%
iGoogle, primed cache
The Importance of Frontend Performance
9% 91%
iGoogle, empty cache
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%April 2008
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 Rules1. Make fewer HTTP
requests2. Use a CDN3. Add an Expires header4. Gzip components5. Put stylesheets at the
top6. Put scripts at the
bottom7. Avoid CSS expressions8. Make JS and CSS
external9. Reduce DNS lookups10.Minify JS11.Avoid redirects12.Remove duplicate
scripts13.Configure ETags14.Make AJAX cacheable
High Performance Web Sites
YSlow
High Performance Web Sites, Vol 2
1. Split the initial payload2. Load scripts without blocking3. Don't scatter inline scripts4. Split dominant domains5. Make static content cookie-free6. Reduce cookie weight7. Minify CSS8. Optimize images9. Use iframes sparingly10.To www or not to www
}part 1
AOLeBayFacebookMySpaceWikipediaYahoo!
Why focus on JavaScript?
YouTube
Scripts Block
<script src="A.js"> blocks parallel downloads and rendering
What's "Cuzillion"?
http://stevesouders.com/cuzillion/?ex=10008
JavaScript
Functions Executed before
onload
www.aol.com 115K 30%
www.ebay.com 183K 44%
www.facebook.com 1088K 9%
www.google.com/search
15K 45%
search.live.com/results
17K 24%
www.msn.com 131K 31%
www.myspace.com 297K 18%
en.wikipedia.org/wiki 114K 32%
www.yahoo.com 321K 13%
www.youtube.com 240K 18%
26% avg252K avg
Initial Payload and Execution
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?
MSNScripts and other resources downloaded in parallel! How? Secret sauce?!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)
MSN.com: Parallel Scripts
Advanced Script Loading
XHR Eval
XHR Injection
Script in Iframe
Script DOM Element
Script Defer
document.write Script Tag
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); };xhrObj.open('GET', 'A.js', true);xhrObj.send('');
http://stevesouders.com/cuzillion/?ex=10009
XHR Injectionvar 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 pagehttp://stevesouders.com/cuzillion/?ex=10015
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 pagewindow.frames[0].createNewDiv();
// access main page from iframeparent.document.createElement('div');
http://stevesouders.com/cuzillion/?ex=10012
Script DOM Elementvar 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<script defer src='A.js'></script>
only supported in IE (just landed in FF 3.1)
script and main page domains can differ
no need to refactor JavaScript
http://stevesouders.com/cuzillion/?ex=10013
document.write Script Tagdocument.write("<scr" + "ipt type='text/javascript' src='A.js'>" + "</scr" + "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
good to show busy indicators when the user needs feedback
bad when downloading in the background
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
immediatelyhttp://stevesouders.com/cuzillion/?ex=10019
Ensure/Avoid Ordered Execution
Summary of Traits
*Only other document.write scripts are downloaded in parallel (in the same script block).
and the winner is...XHR EvalXHR InjectionScript in iframeScript DOM ElementScript Defer
Script DOM ElementScript Defer
Script DOM Element
Script DOM Element (FF)Script Defer (IE)
XHR EvalXHR InjectionScript in iframeScript DOM Element (IE)
XHR InjectionXHR EvalScript DOM Element (IE)
Managed XHR InjectionManaged XHR EvalScript DOM Element
Managed XHR InjectionManaged XHR Eval
Script DOM Element (FF)Script Defer (IE)Managed XHR EvalManaged XHR Injection
Script DOM Element (FF)Script Defer (IE)Managed XHR EvalManaged XHR Injection
different domains same domains
no order
preserve order
no order
no busyshow busy
show busyno busy
preserve order
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 after Stylesheets Block Downloading
Firefox 3 and IE download stylesheets in parallel
...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
eBayMSNMySpaceWikipedia
Examples of Scattered Scripts
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
Announcement 1: UA Profiler
tracks browser performance traits
http://stevesouders.com/ua/
go to the test page
your browser automatically walks through the tests (requires JS)
results recorded and shared publicly
currently 2K+ tests, 1K+ unique testers, 100+ browsers
help out by running the test!
Measuring Performance
Episodes
dev box synthetic testing
bucket testing
real user data
Hammerhead
Announcement 2: Hammerhead
"moving performance testing upstream"http://stevesouders.com/hammerhead/
Firebug extension
load M URLs N times, empty & primed cache
record average & median time
add'l features: export dataload time measurementmodal cache clearing
combine with bandwidth throttler
Facebook Performance Analysis
the good– CDN (Akamai)– future Expires header (~10 days)– gzip turned on– stylesheets at the top (pretty much)– few CSS expressions (4)– JavaScript is minified– no redirects– few ETags (only profile photos)
1. move js below css2. shard across 2 domains3. combine scripts, load async, move lower4. sprite CSS background images5. prefetch resources for next page
1
2
3
4
5
2
Welcome
Home
~150 requests~1M JavaScript
(uncompr)~300K CSS (uncompr)
Home
1. move js below css2. combine stylesheets3. combine scripts, load async, move lower4. sprite CSS background images!!5. reduce size of JS – 85% not used by onload6. reduce size of CSS – 81% (240K) not used by
onload7. optimize images – 44% (97K) lossless
(smushit.com)8. reduce DNS lookups – 15 domains!9. remove ETags on profile photos
Takeaways
focus on the frontend
run YSlow: http://developer.yahoo.com/yslow
this year's focus: JavaScriptSplit the Initial PayloadLoad Scripts without BlockingDon't Scatter Inline Scripts
speed matters
life's too short, write fast code
