How does one go about debugging javascript?

How does one go about debugging javascript?
Do you use firebug and run your page through your localhost?
If javascript is part of an ASP.NET application, I have found that the breakpoints in a .js file in Visual Studio seem to be ignored.
The problem I see is that the ASP.NET application which uses javascript code has too versions — a published and a debug version. The Debug version is located within my group of folders under the localhost. Also, when I launch the program through Visual…
How does one go about debugging javascript?

See original post by xarzu