Transcript High Performance Web Sites 14 rules for faster

Even Faster Web Sites
best practices for faster pages
Steve Souders
[email protected]
http://stevesouders.com/
Disclaimer: This content does not necessarily reflect the opinions of my employer.
The Importance of Frontend
Performance
9%
17%
91%
83%
iGoogle, primed cache
iGoogle, empty cache
Time Spent on the Frontend
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
Empty Cache
97%
Primed Cache
97%
95%
95%
47%
81%
81%
0%
67%
98%
98%
94%
0%
94%
98%
91%
97%
98%
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: vel08st
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 JavaScript?
Yahoo!
Wikipedia
eBay
AOL
MySpace
YouTube
Facebook
Scripts Block
<script src="A.js"> 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/
Split the Initial Payload: Facebook
43 external scripts, 550K uncompressed
9% of functionality is used before onload
Unexecuted Payload
functions not used
before onload
www.aol.com
www.ebay.com
www.facebook.com
www.google.com/search
70%
56%
91%
55%
search.live.com/results
www.msn.com
www.myspace.com
en.wikipedia.org/wiki
76%
69%
82%
68%
www.yahoo.com
www.youtube.com
87%
82%
73.6% 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 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
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
<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
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
IE,FF
FF
IE,FF
IE,FF
no
no
no
no
no
no
no
no
no
no
no
no
IE,FF
FF
IE,FF
FF
no
IE,FF
FF
FF
FF
FF
no
FF
FF
FF
FF
FF
FF
IE,FF
FF
IE,FF
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
normal Script Src
XHR Eval
XHR Injection
Script in Iframe
Script DOM Element
Script Defer
document.write
Script Tag
*Only
size
(bytes)
no
yes
yes
IE,FF
IE,FF
~50
IE,FF
no
no
no
no
~500
IE,FF
no
yes
no
no
~500
IE,FF
no
no
IE,FF
no
~50
IE,FF
yes
yes
FF
FF
~200
IE
yes
yes
IE,FF
IE
~50
IE*
yes
yes
IE,FF
IE
~100
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 setTimeout
move JavaScript 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
eBay
MySpace
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: JavaScript
Split the Initial Payload
Load Scripts without Blocking
Don't Scatter Scripts
speed matters
you CAN make your site even faster!
Steve Souders
[email protected]
http://stevesouders.com/