Hi -
As you know, Tomcat processes Java "servlets" on the client.
As you also know, "Javascript" happens to be downloaded from the server (along with HTML), but it's processed entirely on the client.
Finally, Eclipse allows you to debug Java. It even allows you to debug Java servlets (with the correct configuration).
But I'm not at all sure how you expect to use Eclipse with Javascript.
SUGGESTION:
If you're not already familiar with it, get Firebug:
http://getfirebug.com/javascript
It's absolutely indispensable - for Javascript, CSS and HTML.
Try it - I honestly think you'll like it!
IMHO .. PSM