Users use NotePad, TextPad, or Notepad++ to name a few.
I don't use this feature because for it to work you have to completely
close the editor each time you want to apply a change, which makes it
useless to me. I use Notepad++ as an external editor where I write the
code, and then I paste it into the internal editor when I want to run it.
Notepad++ offers visual cues, JS-syntax coloring, version comparisons, and
many (many) other features.
In situations where the code is too long for the internal editor and I have
to use an external one, I use Notepad because it's easy to open it, enter
the code (again, having edited it in Notepad++), save and close it in a
matter of seconds.
I'll second the recommendation for Notepad++ as it's free and fast and it does what you want. I don't find closing the editor each time to be a problem, except on a Mac.
I just tried notepad++ and I've got to admit it's pretty much what I need. However, I can't find how to set JS-synthax coloring. In the Language tab, the only languages listed are JAVA and JSP although JAVA seems to have a similar synthax. DO you set it to JAVA or is there a separate JS plugin I need to install?
I'm not sure why it would be missing in yours.