JCreator is a powerful IDE for Java. JCreator provides the user with a wide range of functionality such as : Project management, project templates, code-completion, debugger interface, editor with syntax highlighting, wizards and a fully customizable user interface. It has Popup code completion, code snippets, JSP, Ant and CVS support and much more. But most interesting it is written for newbies in mind.
Next comes Eclipse which is an open source IDE. It is also very good. Since you are looking for java script only then you can go for JCreator Academic editions it is free for students.
www.eclipse.org