Extending Native Date Continued (Part II)

About 6 months ago, I wrote several articles about extending the native JavaScript Date Object with constants, static methods, and public methods on the prototype:

Date Functions
YUI Datemath on JavaScript Date Object

The first article describes methods that I designed myself, while the second explains how to convert YUI Datemath to extend the Date Object instead of using static methods. I recently revisited all the methods that I append to Date and Date.prototype, creating a JavaScript unit test using the YUI Test Framework. While they all worked before, I have re-written them now to handle errors and bad parameters better than before. As noted in the comments, many of them return default values, or NULL when enough parameters are not provided.

Check out the new Date.js here and the unit test here if you want to double check that it all works well on your favorite browser.