I'm learning javascript and I thought it would be fun to build a "simple" calculator. I spent a few hours coding, and implementing the functions, but it only works partially. Can one of you look at my code and try and figure out what's wrong? The Calculator.zip Here's some explanation of the issues:

1. the add(), subtract(), multiply(), and divide() methods work partially, not at all, or don't do as they're supposed to..
2. sometimes the 0 wont clear when the replaceDisplay() method evaluates the screen.

If it helps, I'm also using jquery, so keep that in mind. Thank you!