A talk I gave October 2008 at the Web Experience Forum in Boston.

1. Performance
Improvements in
Browsers
John Resig
http://ejohn.org/ - http://twitter.com/jeresig/

2. About Me
✦ Work for the Mozilla Corporation (Firefox!)
✦ Do a lot of JavaScript performance analysis
✦ Dromaeo.com is my performance test suite
✦ Tests the performance of JavaScript engines
✦ Tests the performance of browser DOM
✦ Work on Firebug (great developer tool)
✦ Creator of the jQuery JavaScript Library
✦ http://jquery.com/
✦ Used by Microsoft, Google, Adobe, Nokia,
IBM, Intel, CBS News, NBC, etc.

3. Upcoming Browsers
✦ The browsers:
✦ Firefox 3.1
✦ Safari 4
✦ Internet Explorer 8
✦ Opera 10
✦ Google Chrome
✦ Defining characteristics:
✦ Better performance
✦ Advanced JavaScript engines

4. Firefox 3.1
✦ Set to be released Spring 2009
✦ Goals:
✦ Performance improvements
✦ Video and Audio tags
✦ Private browsing
✦ Beta 1 just released
✦ http://developer.mozilla.org/En/Firefox_3.1_for_developers

5. Safari 4
✦ Released in conjunction with OS X 10.6
✦ Features:
✦ Performance improvements
✦ Desktop Apps
✦ ACID 3 compliance
✦ Revamped dev tools
✦ Preview seeded to developers
✦ http://webkit.org/blog/

6. Internet Explorer 8
✦ Released late 2008/early 2009
✦ Features:
✦ Backwards compatibility with IE 7
✦ Web Clips (trim out a part of a page and
place on desktop)
✦ Process per tab
✦ Beta 2 recently
released
✦ http://www.microsoft.com/
windows/internet-explorer/
beta/readiness/new-features.aspx

7. Opera 10
✦ Unspecified release schedule (2009?)
✦ Features:
✦ ACID 3 compliance
✦ Video and Audio tags
✦ Opera 9.6 recently released
✦ http://labs.opera.com/

8. Google Chrome
✦ Released September 2008
✦ Features:
✦ Private browsing
✦ Process per tab
✦ Next release schedule unknown
✦ http://googlechromereleases.blogspot.com/

9. Process Per Tab
✦ Most browsers have a single process
✦ Share memory, resources
✦ Pages rendered using threads
✦ IE 8 and Chrome split tabs into individual
processes
✦ What does this change?
✦ Pages can do more processing
✦ (Not block the UI or other tabs)
✦ Tabs consume more memory

10. Process Per Tab
✦ Examples of changes, in Chrome.
✦ Timer speed is what you set it to.
✦ Browsers cap the speed to 10ms.
✦ setInterval(fn, 1);
✦ Can do more non-stop processing, without
warning:
while (true) {}
✦ Chrome has a process manager (like the
OS process manager - see CPU, Memory)

11. JavaScript Engines
✦ New wave of engines:
✦ Firefox: TraceMonkey
✦ Safari: SquirrelFish (Extreme)
✦ Chrome: V8
✦ Continually leap-frogging each other

12. Measuring Speed
✦ SunSpider
✦ Released by the WebKit team last fall
✦ Focuses completely on JavaScript
✦ Dromaeo
✦ Released by Mozilla this spring
✦ Mix of JavaScript and DOM
✦ V8 Benchmark
✦ Released by Chrome team last month
✦ Lots of recursion testing
✦ Quality: http://ejohn.org/blog/javascript-benchmark-quality/

13. http://ejohn.org/blog/javascript-performance-rundown/

14. http://ejohn.org/blog/javascript-performance-rundown/

15. http://ejohn.org/blog/javascript-performance-rundown/

16. Recent Numbers
http://arstechnica.com/journals/linux.ars/2008/10/07/extreme-javascript-performance

17. Recent Numbers
http://arstechnica.com/journals/linux.ars/2008/10/07/extreme-javascript-performance

18. Network

19. Network
✦ Steve Souders is the man.
✦ http://stevesouders.com/ua/
✦ YSlow

20. Simultaneous Conn.
✦ Number of downloads per domain
✦ Should be at least 4
✦ FF 2, IE 6, and IE 7 are 2
✦ Safari is 4
✦ Everyone else is 6-7
✦ Max connections: Number of simultaneous
downloads
✦ Firefox, Opera: 25-30
✦ Everyone else: 50-60

21. Parallel Scripts
✦ Download scripts simultaneously
✦ Even though they must execute in order
✦ <script defer>
✦ From Internet Explorer
✦ Just landed for Firefox 3.1
✦ Replacement for JavaScript-based
loading

22. Redirect Caching
✦ A simple request:
http://foo.com ->
http://www.foo.com ->
http://www.foo.com/
✦ Very costly, should be cached.
✦ Chrome and Firefox do well here.

23. Link Prefetching
✦ <link rel=”prefetch” href=”someimg.png”/>
✦ Pre-load resources for later use
✦ (images, stylesheets)
✦ Currently only in Firefox
✦ Replacement for JavaScript preloading

24. DOM Navigation

25. Class Name
✦ New method:
getElementsByClassName
✦ Works just like:
getElementsByTagName
✦ Fast way of finding elements by their class
name(s):
<div class=”person sidebar”></div>
✦ document.getElementsByClassName(“sidebar”)
✦ Safari 3.1 and Firefox 3.0
✦ Drop-in replacement for existing queries

26. Speed Results
http://ejohn.org/blog/getelementsbyclassname-speed-comparison/

27. Selectors API
✦ querySelectorAll
✦ Use CSS selectors to find DOM elements
✦ document.querySelectorAll(“div p”)
✦ Good cross-browser support
✦ IE 8, Safari 4, FF 3, Opera 10
✦ Drop-in replacement for JavaScript
libraries.

28. Speed Results
http://www2.webkit.org/perf/slickspeed/

29. JavaScript Threads
✦ JavaScript has always been single-threaded
✦ Limited to working linearly
✦ New HTML 5 Web Workers
✦ Spawn JavaScript threads
✦ Run complicated work in the background
✦ Doesn’t block the browser!
✦ Demo: http://ejohn.org/apps/threads/
✦ Drop-in usable, huge quality boost.

30. Styling and Effects
✦ Lots of commons styling effects
✦ Can be replaced and simplified by the
browser
✦ Drastically simplify pages and improve
their performance

31. Rounded Corners
✦ CSS 3 specification
✦ Implemented in Safari, Firefox, Opera
✦ -moz-border-radius: 5px;
✦ -webkit-border-radius: 5px;
✦ Can replace clumsy, slow, old methods.

32. Shadows
✦ Box Shadows
✦ Shadow behind a div
✦ -webkit-box-shadow: 5px 5px 5px rgba(0, 0, 0, 0.5)
✦ Text Shadows
✦ Shadow behind some text
✦ text-shadow: -1px -1px #666, 1px 1px #FFF;
✦ Implemented in WebKit, Firefox
✦ Can replace clumsy, slow, old methods.

33. Example Shadows
✦ Demos: http://maettig.com/code/css/text-
shadow.html
http://webkit.org/blog/86/box-shadow/

34. Custom Fonts
✦ Load in custom fonts
✦ Can load TrueType fonts
✦ Implemented in Safari and Firefox
✦ Demo: http://ejohn.org/apps/fontface/
blok.html
✦ Can replace using Flash-based fonts.

35. Transforms and Animations
✦ Transforms allow you to rotate, scale, and
offset an element
✦ -webkit-transform: rotate(30deg);
✦ Animations allow you to morph an
element using nothing but CSS
✦ -webkit-transition: all 1s ease-in-out;
✦ Implemented in WebKit and Firefox
✦ Demo: http://www.the-art-of-web.com/css/
css-animation/
✦ Can replace JS animations, today.

36. Canvas
✦ Proposed and first implemented by Apple
in WebKit
✦ A 2d drawing layer
✦ With possibilities for future expansion
✦ Embedded in web pages (looks and
behaves like an img element)
✦ Works in all browsers (IE with ExCanvas)
✦ Offload rendering to client
✦ Better user interaction

37. Shapes and Paths
✦ NOT vectors (unlike SVG)
✦ Rectangles
✦ Arcs
✦ Lines
✦ Curves
✦ Charts:

38. Fill and Stroke
✦ All can be styled (similar to CSS)
✦ Stroke styles the path (or outline)
✦ Fill is the color of the interior
✦ Sparklines:

39. Canvas Embedding
✦ Canvases can consume:
✦ Images
✦ Other Canvases
✦ Will be able to consume (Firefox 3.1):
✦ Video
✦ In an extension:
✦ Web Pages

40. Data

41. Native JSON
✦ JSON is a format for transferring data
✦ (Uses JavaScript syntax to achieve this.)
✦ Has been slow and a little hacky.
✦ Browser now have native support in
Firefox 3.1 and IE 8
✦ Drop-in usable, today
✦ JSON.encode(object)
✦ JSON.decode(string)

42. Performance
✦ Encoding:
✦ Decoding:

43. New Measurements

44. Painting
✦ When something is physically drawn to
the screen
✦ Hard to quantify without more
information
✦ Firefox 3.1 includes a new event:
MozAfterPaint
✦ Demo: http://ejohn.org/blog/browser-
paint-events/

45. Reflow
✦ CSS has lots of boxes in it
✦ Position of boxes is constantly recomputed
and repositioned (before being painted)
✦ This is reflow
✦ Demo: http://dougt.wordpress.com/
2008/05/24/what-is-a-reflow/

46. Questions?
✦ John Resig
http://ejohn.org/
http://twitter.com/jeresig/