ProgrammersHelp.co.uk JavaScript 1.5 Reference
Extensive documentation on the JavaScript language. Recommended if you would like to learn the event handlers, standard functions, objects, and other information.

ECMAScript- ECMA-262
Documentation for ECMAScript.

Microsoft JScript
This leads to documentation on JScript, the version of JavaScript used in Microsoft Internet Explorer. Includes a JScript guide, reference, and more.