By default, you can use notepad to view JavaScript source code. To change it, follow these steps:
Quit Internet Explorer (if it is running).
Double-click My Computer.
On the View menu, click Options (or Folder Options).
Click the File Types tab. In the Registered File Types box, find JavaScript, click it, and then click Edit. Then select your editor.
Note: If it is not works, you may need to type a space and %1 at the end of the command. For example, if you want to use Notepad to be your default HTML editor, type the following command:
c:\windows\notepad.exe "%1"
OK, click Close, and then click Close again.
Reference: http://support.microsoft.com/kb/163606/en-us
Does it really work? I don't know. But try it, please.