Using notepad makes no sense at all, just because the particular "editor" is below any reasonable minimal requirements: it cannot even show position of a cursor. Even a minimal home-made editor based on standard Windows or .NET Forms or WPF control could do much better. So, I don't think this is a reasonable option in practice. But editors based, say, on Scintilla, such as Notepad2, Notepad++ or SciTE would do even better.
See:
http://en.wikipedia.org/wiki/Scintilla_%28editing_component%29[
^]
http://en.wikipedia.org/wiki/Notepad%2B%2B[
^],
http://www.notepad-plus-plus.org/[
^];
http://en.wikipedia.org/wiki/Notepad2[
^],
http://www.flos-freeware.ch/notepad2.html[
^];
http://en.wikipedia.org/wiki/SciTE[
^],
http://www.scintilla.org/SciTE.html[
^].
Much more useful could be some IDE. Try Open Source Aptana Studio; see:
http://en.wikipedia.org/wiki/Aptana_Studio[
^];
http://www.aptana.org/[
^].
Another good thing is SharpDevelop, see:
http://en.wikipedia.org/wiki/SharpDevelop[
^],
http://sharpdevelop.com/[
^]. It has a good text editor component AvalonEdit, which you can compile and use in your own text editor. You can download it with SharpDevelop source code; see:
http://wiki.sharpdevelop.net/AvalonEdit.ashx[
^].
See also CodeProject article:
Using AvalonEdit (WPF Text Editor)[
^].
To me, the best one is Visual Studio, which you can use for JavaScript editing and step-by-step debugging in the context of your Web site:
http://en.wikipedia.org/wiki/Visual_Studio[
^];
http://www.microsoft.com/visualstudio/en-us[
^].
You can always use its free edition, Visual Studio Express:
http://en.wikipedia.org/wiki/Visual_Studio_Express[
^],
http://www.microsoft.com/visualstudio/en-us/products/2010-editions/express[
^].
Good luck,
—SA