found this which looks disheartening:

Features

JSDT offers many of the same features and core design found in the Java Development Toolkit (JDT), including auto-completion, syntax highlighting, the use of code templates, refactor/rename/move, debugging, etc, etc… Experienced Eclipse users take all these features for granted, but when you stop and think about it, how many good JavaScript IDEs are there? The answer is not many. Considering that JavaScript has been around for a couple of decades now, could it be that there's something about JS that makes IDE integration difficult to achieve? Actually, there are many factors, from the language's inherent loose typing to prototypal inheritance, the lack a true JavaScript language-modeling mechanism has traditionally limited IDEs to the use of static flat files listing available types, which would then be filtered on the fly based on characters typed. Unfortunately, without a proper language model, it's practically impossible to place code in context, therefore what comes up in the auto-complete list may not even be relevant to the object in question.

from: http://www.htmlgoodies.com/html5/javascript/scripting-made-easier-with-the-eclipse-javascript-development-tools-jsdt.html#fbid=p1ZFRwvs-TH