Web Coding & Development All-in-One For Dummies, 2nd Edition

Chapter 2

Debugging JavaScript Code

IN THIS CHAPTER

Learning JavaScript’s error types

Debugging errors by using the Console window

Setting breakpoints

Watching variable and expression values

Learning JavaScript’s most common errors and error messages

Testing proves a programmer’s failure. Debugging is the programmer’s vindication.

— BORIS BEIZER

It usually doesn’t take too long to get short scripts and functions up and running. However, as your code grows larger and more complex, errors inevitably creep in. In fact, it has been proven mathematically that any code beyond a minimum level of complexity will contain at least one error, and probably quite a lot more.

Many of the bugs that crawl into your code will consist of simple syntax problems that you can fix quickly, but others will be more subtle and harder to find. For the latter — whether the errors are incorrect values returned by functions or problems with the overall logic of a script — you need to be able to get inside your ...