View http://javascriptweblog.wordpress.com/2011/02/07/truth-equality-and-javascript
Checking for truthiness and equality in JavaScript can sometimes be a daunting procedure. This article heavily walks through the ins and outs of effectively evaluating truth and equality in JavaScript. This is an important thing to understand as fully as possible because it correlates directly to business logic and overall stability of your code. Beyond that, these checks often tie in directly to any and all security measures that have been put in place, an area in which false positives can be detrimental.