Even Faster Web Sites
http://stevesouders.com/docs/jquery-20090913.ppt
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
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
Sept 2007
June 2009
Even Faster Web Sites
Splitting the initial payload
Loading scripts without blocking
Coupling asynchronous scripts
Positioning inline scripts
Sharding dominant domains
Flushing the document early
Using iframes sparingly
Simplifying CSS Selectors
Understanding Ajax performance..........Doug Crockford
Creating responsive web apps............Ben Galbraith, Dion Almaer
Writing efficient JavaScript.............Nicholas Zakas
Scaling with Comet.....................Dylan Schiemann
Going beyond gzipping...............Tony Gentilcore
Optimizing images...................Stoyan Stefanov, Nicole Sullivan
Why focus on JavaScript?
Yahoo!
Wikipedia
eBay
AOL
MySpace
YouTube
Facebook
scripts block
<script src="A.js"> blocks parallel
downloads and rendering
9 secs: IE 6-7, FF 3.0, Chr 1, Op 9-10, Saf 3
7 secs: IE 8, FF 3.5, Chr 2, Saf 4
initial payload and execution
JavaScript
Functions Executed
before onload
www.aol.com
www.ebay.com
www.facebook.com
www.google.com/search
115K
183K
1088K
15K
30%
44%
9%
45%
search.live.com/results
www.msn.com
www.myspace.com
en.wikipedia.org/wiki
17K
131K
297K
114K
24%
31%
18%
32%
www.yahoo.com
www.youtube.com
321K
240K 252K avg
13%
18% 26% avg
splitting 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? 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)
Loading Scripts Without Blocking
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
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
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');
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
Script Defer
<script defer src='A.js'></script>
supported in IE and FF 3.1+
script and main page domains can differ
no need to refactor JavaScript
document.write Script Tag
document.write("<script
type='text/javascript' src='A.js'>
<\/script>");
parallelization only works in IE
parallel downloads for scripts, nothing else
all document.writes must be in same
script block
Load Scripts Without Blocking
||
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...
XHR Eval
XHR Injection
Script in iframe
Script DOM Element
Script Defer
same domains
different domains
Script DOM Element
Script Defer
no order
no order
preserve order
XHR Eval
XHR Injection
Script in iframe
Script DOM Element (IE)
preserve order
Script DOM Element (FF)
Script Defer (IE)
Managed XHR Eval
Managed XHR Injection
Script DOM Element
no busy
Script DOM Element (FF)
Script Defer (IE)
Managed XHR Injection
Managed XHR Eval
no busy
XHR Injection
XHR Eval
Script DOM Element (IE)
show busy
Managed XHR Injection
Managed XHR Eval
Script DOM Element
show busy
Script DOM Element (FF)
Script Defer (IE)
Managed XHR Eval
Managed XHR Injection
asynchronous JS example: menu.js
script DOM element approach
<script type="text/javascript">
var domscript = document.createElement('script');
domscript.src = "menu.js";
document.getElementsByTagName('head')[0].appendChild(domscri
pt);
var aExamples =
[
['couple-normal.php', 'Normal Script Src'],
['couple-xhr-eval.php', 'XHR Eval'],
...
['managed-xhr.php', 'Managed XHR']
];
function init() {
EFWS.Menu.createMenu('examplesbtn', aExamples);
}
init();
</script>
before
after
Loading Scripts Without Blocking
||
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
IE
yes
yes
IE,FF
FF !IE ~200
IE
~50
IE*
yes
yes
IE,FF
IE
other document.write scripts are downloaded in parallel (in the same script block).
~100
what about
inlined code
that depends on the script?
coupling techniques
hardcoded callback
window onload
timer
degrading script tags
script onload
technique 5: script onload
<script type="text/javascript">
var aExamples = [['couple-normal.php', 'Normal Script Src'], ...];
function init() {
EFWS.Menu.createMenu('examplesbtn', aExamples);
}
var domscript = document.createElement('script');
domscript.src = "menu.js";
domscript.onloadDone = false;
domscript.onload = function() {
if ( ! domscript.onloadDone ) { init(); }
domscript.onloadDone = true;
};
domscript.onreadystatechange = function() {
if ( "loaded" === domscript.readyState ) {
if ( ! domscript.onloadDone ) { init(); }
domscript.onloadDone = true;
}
}
document.getElementsByTagName('head')[0].appendChild(domscript);
</script>
pretty nice, medium complexity
asynchronous loading & coupling
async technique: Script DOM Element
easy, cross-browser
doesn't ensure script order
coupling technique: script onload
fairly easy, cross-browser
ensures execution order for external script
and inlined code
multiple interdependent external and
inline scripts:
much more complex (see hidden slides)
concatenate your external scripts into one!
takeaways
focus on the frontend
run YSlow
(http://developer.yahoo.com/yslow)
and Page Speed!
(http://code.google.com/speed/page-speed/)
speed matters
impact on revenue
Bing: +2000 ms  -4.3% revenue/user1
Yahoo: +400 ms  -5-9% full-page traffic
2
Google: +400 ms  -0.59% searches/user1
AOL: fastest users  +50% page views3
Shopzilla: -5000 ms  +7-12% revenue4
1
2
3
4
http://en.oreilly.com/velocity2009/public/schedule/detail/8523
http://www.slideshare.net/stoyan/yslow-20-presentation
http://en.oreilly.com/velocity2009/public/schedule/detail/7579
http://en.oreilly.com/velocity2009/public/schedule/detail/7709
cost savings
hardware – reduced load
Shopzilla – 50% fewer servers
bandwidth – reduced response size
http://billwscott.com/share/presentations/2008/stanford/HPWP-RealWorld.pdf
if you want
better user experience
more revenue
reduced operating costs
the strategy is clear
Even Faster Web Sites
book signing now
Steve Souders
souders@google.com
http://stevesouders.com/docs/jquery-20090913.ppt