Yahoo's YUI team released a new version of its popular open-source Ajax framework. YUI has become one of the significant Ajax client libraries, in part because of its well-designed architecture, and in part because of its rich and attractive UI components.

The latest version of YUI includes a CSS3 selector engine. This allows client code to quickly access CSS selectors on a page:

Most major libraries have now added selector functionality, and there’s an emerging body of work that helps implementers sort out the relative performance profiles of the various tools. The YUI Selector Utility implements much of the CSS Selector syntax as defined by the W3C, including the proposed CSS3 Selector extensions.

The new YUI charting controls are the results of the YUI team collaborating with Yahoo's Flash developers:

[The charting control] is a hybrid JavaScript/Flash component that supports bar, line, and pie charts. The Charts Control draws data from the same DataSource Utility that underpins the YUI DataTable Control, making it possible to do combined chart/table visualizations. The Charts Control accepts CSS style information, allowing you to skin the chart itself without touching the underlying .swf file.

Another new component is a Get utility:

Get provides an interface for dynamically adding script nodes and CSS link nodes to the page. This is the same engine we use in the YUI Loader Utility; with 2.4.0, we’ve reorganized the functionality and made it available as a separate module. You’ll find the Get Utility useful for loading JavaScript and CSS on an as-needed basis and for proxyless web-services calls where you’re retrieving JSON data.

YUI 2.4 now also includes a profiler:

Profiler allows you to target specific code for profiling and to retrieve profiling data programmatically while your application is running — in any A-Grade browser.

Another new utility makes it easier to work with JSON on the client, based on Douglas Crockford’s public-domain JSON parse and stringify functionality.

Finally, YUI 2.4 includes numerous enhancements to existing components, such as the rich text editor:

With 2.4.0, you can better control the dependency list, allowing you to shave more than 50% off the overall k-weight of the widget (vs. its 2.3.1 profile) if you don’t need some of the glossier UI elements.

What do you think of the Yahoo YUI library?