Yahoo! recommends YUI 3. Learn about the YUI 3 Global Object on YUILibrary.com.
The YAHOO Global Object lives at the top of the namespace tree for all YUI components. It also includes some utility methods for type-checking, user-agent detection, and module extension.
YAHOO.lang type checking methods to deal with unpredictable dataYAHOO.env.ua can tell you with some accuracy which browser your page is being viewed in.YAHOO.lang.extend: Leverage class inheritance in an object-oriented architecture.YAHOO.lang.augmentProto: Use YAHOO.lang.augmentProto to help modularize class behaviors.YAHOO.lang.augmentObject: Use augmentObject to extend static classes, object literals, or class instances.YAHOO.lang.merge: Merge several objects, creating a unique set.All YUI 2.x users should review the YUI 2.8.2 security bulletin, which discusses a vulnerability present in YUI 2.4.0-2.8.1.

Copyright © 2012 Yahoo! Inc. All rights reserved.