Good JavaScript IDE with jQuery support

I'm planning to start learning jQuery (among other things), so I'm looking for a good Javascript editor that can preferably provide some of the following features:

What can I use as a Notepad++ alternative in Linux (Ubuntu)?

I got addicted to Notepad++ on Windows and I've recently moved to Ubuntu. I'm missing a tool as such.

How do I convert dos files to linux files in vim?

If I open files I created in windows, the lines all end with ^M.