If you are web developer you may have noticed that the latest version of Yahoo’s User Interface toolset and widgets (for web development), YUI 3.0, is now available as a preview release. YUI has long been a popular “Ajax” library both because of its liberal BSD license, and because of the number of features it provides.

The big news about YUI the third are that it changes from the root and (unfortunately) is not compatible with YUI 2.x APIs as Eric and Matt stated on developer blog.

YUI 3.0 builds off of the YUI 2.x codeline, but we’ve evolved most of the core APIs in working toward the five key goals described above. As a result, migrating from YUI 2.x to 3.x will require effort at the implementation level.

However, YUI 3.0 will ship with a limited compatibility layer for the current YUI Core that will allow you to run some of your YUI 2.x-based implementations (Yahoo Global Object, Dom Collection, and Event Utility) on top of YUI 3.0.

These radical changes are toward 5 goals:

• Lighter (less K-weight on the wire and on the page for most uses)
• faster (fewer http requests, less code to write and compile, more efficient code)
• more consistent (common naming, event signatures, and widget APIs throughout the library)
• more powerful (do more with less implementation code)
• more securable (safer and easier to expose to multiple developers working in the same environment; easier to run under systems like Caja or ADsafe)

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Mozilla has just introduced a new JavaScript optimization feature to Firefox 3.1 development code base (Shiretoko) that well enhances JavaScript-based web apps performance by a 2x – 20x fold compared to the Firefox 3.0, according to JavaScript performance tests ran and published by Mozilla’s Brendan Eich.

I’m extremely pleased to announce the launch of TraceMonkey, an evolution of Firefox’s SpiderMonkey JavaScript engine for Firefox 3.1 that uses a new kind of Just-In-Time (JIT) compiler to boost JS performance by an order of magnitude or more.

Here are some of the charts from Brendan’s blog:

Assorted benchmarks

SunSpider micro-benchmarks

However the best way to evaluate it is to see it in action via simple JavaScript image editor that lets you adjust a picture’s contrast and brightness with a couple of sliders created by Mike Schroepfer. By default, TraceMonkey is disabled (as it is still buggy), there is a very noticeable delay while sliding. Turn it on (javascript.options.jit.content = true in about:config) and the thing works like charm, very smoothly.

JavaScript Image Editor

Going into significant detail on how all of this came about, Brendan notes some key points:

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