best-practices for performance
description
Transcript of best-practices for performance
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Steve [email protected]://stevesouders.com/
Even Faster Web Sites best practices for faster pages
Disclaimer: This content does not necessarily reflect the opinions of my employer.
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17%
83%
iGoogle, primed cache
The Importance of Frontend Performance
9% 91%
iGoogle, empty cache
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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%
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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
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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
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High Performance Web Sites
YSlow
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http://conferences.oreilly.com/velocity/ 20% discount: vel08st
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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
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AOLeBayFacebookMySpaceWikipediaYahoo!
Why focus on JavaScript?
YouTube
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Scripts Block
<script src="A.js"> blocks parallel downloads and rendering
What's "Cuzillion"?
http://stevesouders.com/cuzillion/?ex=10008
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a tool for quickly constructing web pages to see how components interact
Open Source
http://stevesouders.com/cuzillion/
Cuzillion'cuz there are a zillion pages to check
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Initial Payload and Execution
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
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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?
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MSNScripts 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)
MSN.com: Parallel Scripts
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Advanced Script Loading
XHR Eval
XHR Injection
Script in Iframe
Script DOM Element
Script Defer
document.write Script Tag
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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
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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
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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
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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
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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
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document.write Script Tagdocument.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
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Browser Busy Indicators
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Browser Busy Indicators
good to show busy indicators when the user needs feedback
bad when downloading in the background
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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
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Summary of Traits
*Only other document.write scripts are downloaded in parallel (in the same script block).
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and the winner is...
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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?
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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 techniquesuse Defer attribute (IE only)
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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
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eBayMSNMySpaceWikipedia
Examples of Scattered Scripts
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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
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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
you CAN make your site even faster!
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Steve [email protected]://stevesouders.com/