Yahoo User Interface Library

http://developer.yahoo.net/yui/

The Yahoo! User Interface Library is a set of utilities and controls, written in JavaScript, for building richly interactive web applications using techniques such as DOM scripting, HTML and AJAX.

The UI Library Utilities facilitate the implementation of rich client-side features by enhancing and normalizing the developer's interface to important elements of the browser infrastructure (such as events, in-page HTTP requests and the DOM).

The Yahoo UI Library Controls produce visual, interactive user interface elements on the page with just a few lines of code and an included CSS file. All the components in the Yahoo! User Interface Library have been released as open source under a BSD license and are free for all uses.

If there is one thing to love about this library, it's the documentation. From day one, every available component has full API documentation as well as a short "Getting Started" guide complete with working examples. No trawling through the developers' blogs, no pulling apart complex applications: this toolkit has all the spit and polish of a commercial product.

For now, the library's scope is somewhat limited. Beyond the core utilities for animation, remote scripting (AJAX), event handling, DOM manipulation, and drag-and-drop (which are certainly nothing to sneeze at!), the library currently offers only three actual widgets for building user interfaces:

Calendar for selecting dates
Slider for visually choosing from a range of values
TreeView for browsing through a hierarchy of items
Though the selection isn't overwhelming, these three widgets alone already solve some problems that have traditionally taken a lot of work to overcome. No doubt future widget releases will address some of the more mundane needs of web application user interfaces.

It's particularly refreshing to see Yahoo! opening up its box of goodies and sharing them with the web development community. This move contrasts sharply with Google's approach of protecting its JavaScript assets by hiding them away in obfuscated code.