1. Even Faster Web Sites best practices for faster pages
Permission to use photo given by Amnemona:
Steve Souders
Disclaimer: This content does not necessarily reflect the opinions of my employer.

2. The Importance of Frontend Performance9%
91%
17%
83%
iGoogle, primed cache
Data source: Steve Souders
Tested on IE6 on Comcast cable modem (~5 mbps) medium powered PC, April 2008.
iGoogle, empty cache

3. Time Spent on the Frontend
Empty Cache
Primed Cache
97%
95%
81%
47% 0%
search.live.com/results
67%
98%
94%
en.wikipedia.org/wiki
91%
96%
Ten top sites according to Alexa.com.
Data source: Steve Souders
Tested on IE6 on Comcast cable modem (~5 mbps) medium powered PC, April 2008.
For Google and Live Search there are so few components (2-4) and they're mostly cacheable so the HTML document is a bigger percentage.

4. The Performance Golden Rule
80-90% of the end-user response time is
spent on the frontend. Start there.
greater potential for improvement
simpler
If you could cut performance in half, FE changes would be 40-45%, while BE would be only 5-10%.
BE changes are typically more complex: rearchitecture, optimize code, add/modify hw, distribute databases, etc.
FE is simpler: change web server config, place scripts and stylesheets differently in the page, combine requests, etc.
I’ve worked with dev teams to cut response times on 50 properties, often by 25% or more. And feedback from other companies is similar.
Permission to use photo given by Technicolor:
proven to work

5. 14 Rules Make fewer HTTP requests Use a CDN Add an Expires header
Gzip components
Put stylesheets at the top
Put scripts at the bottom
Avoid CSS expressions
Make JS and CSS external
Reduce DNS lookups
Minify JS
Avoid redirects
Remove duplicate scripts
Configure ETags
Make AJAX cacheable
photo courtesy of Vicki & Chuck Rogers:

6. YSlow
High Performance Web Sites

7. http://conferences.oreilly.com/velocity/ 20% discount: vel08st

8. High Performance Web Sites, Vol 2
Split the initial payload
Load scripts without blocking
Don't scatter inline scripts
Split dominant domains
Make static content cookie-free
Reduce cookie weight
Minify CSS
Optimize images
Use iframes sparingly
To www or not to www

9. Why focus on JavaScript?
Yahoo!
YouTube
AOL
Wikipedia
eBay
Facebook
MySpace
Data Source: Steve Souders
aol 76%
ebay 45%
facebook 41%
google 42%
live search 9%
msn 37%
myspace 37%
yahoo 45%
youtube 60%
wikipedia 26%
average 42%

10. Scripts Block
<script src="A.js"> blocks parallel downloads and rendering
What's "Cuzillion"?

11. Cuzillion 'cuz there are a zillion pages to check
a tool for quickly constructing web pages to see how components interact
Open Source

12. Initial Payload and Execution
JavaScript
Functions Executed before onload
115K
30%
183K
44%
1088K 9%
15K
45%
search.live.com/results
17K
24%
131K
31%
297K
18%
en.wikipedia.org/wiki
114K
32%
321K
13%
240K
Data source: Steve Souders
252K avg
26% avg

13. 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?
Permission to use photo given by Brian.H -

14. MSN.com: Parallel Scripts
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)
Of the ten top sites, MSN.com (Script DOM Element), Live Search (Script in Iframe), and Yahoo (Script DOM Element) use advanced script loading techniques.

15. Advanced Script Loading
XHR Eval
XHR Injection
Script in Iframe
Script DOM Element
Script Defer
document.write Script Tag
All of these allow for parallel downloads, but none of them allow for parallel JS execution – that's not possible (currently, WebKit is doing some stuff on that).

16. XHR Eval script must have same domain as main page
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

17. XHR Injection script must have same domain as main page
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

18. Script in Iframe iframe must have same domain as main page
<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');

19. Script DOM Element script and main page domains can differ
var se = document.createElement('script');
se.src = '
document.getElementsByTagName('head')
[0].appendChild(se);
script and main page domains can differ
no need to refactor JavaScript

20. Script Defer only supported in IE
<script defer src='A.js'></script>
only supported in IE
script and main page domains can differ
no need to refactor JavaScript

21. document.write Script Tag
"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

22. Browser Busy Indicators
Audio (IE "click") is another busy indicator.
Delayed rendering and delayed onload ("done") are other busy indicators.
Sometimes busy indicators are bad, sometimes good.

23. Browser Busy Indicators
status
bar
progress
logo
cursor
block
render
onload
normal Script Src FF
IE,FF
XHR Eval no
XHR Injection
Script in Iframe
Script DOM Element
Script Defer
document.write Script Tag
Data source: Steve Souders
Audio (IE "click") is another busy indicator.
Delayed rendering and delayed onload ("done") are other busy indicators.
Sometimes busy indicators are bad, sometimes good.
good to show busy indicators when the user needs feedback
bad when downloading in the background

24. Ensure/Avoid Ordered Execution
Ensure scripts execute in order:
necessary when scripts have dependencies
IE:
FF:
Avoid scripts executing in order:
faster – first script back is executed immediately

25. Summary of Traits normal Script Src XHR Eval XHR Injection
|| down-loads
domains can differ
existing scripts
browser busy
ensures order
size (bytes)
normal Script Src no
yes
IE,FF
~50
XHR Eval
~500
XHR Injection
Script in Iframe
Script DOM Element FF
~200
Script Defer IE
document.write Script Tag
IE*
~100
Data source: Steve Souders
*Only other document.write scripts are downloaded in parallel (in the same script block).

26. and the winner is...
I'll do JavaScript and PHP implementations of this logic soon.

27. 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?
Permission to use photo given by Reciprocity:

28. Inline Scripts Block
long executing inline scripts block rendering and downloads
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)

29. 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
best to move inline scripts above stylesheets or below other resources
use Link,
Joseph Smarr from Plaxo advocates interspersing setTimeout through JavaScript threads every n00 ms.

30. Examples of Scattered Scripts
Wikipedia
MySpace
eBay
MSN
Data source: Steve Souders

31. 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
Permission to use photo given by _iosonoshuo_:

32. Takeaways focus on the frontend
run 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!

33. Steve Souders souders@google.com http://stevesouders.com/
"thank you" by nj dodge:
Steve Souders