There is a JavaWorld article titled Ajax: Tools of the trade, which consists of a survey of tools for the JavaScript developer.
The article starts by mentioning the JavaScript support offered by popular IDEs such as NetBeans, IntelliJ, and Eclipse. It continues with describing tools such as Firebug (lets you edit, debug, and monitor JavaScript on the fly), YSlow (analysis webpages and suggests ways to imporve performance), and Hammerhead (measures the load time of web pages).
The next part of the article goes into ways of testing your JavaScript code, by using tools and frameworks such as JsUnit (unit testing framework for JavaScript), JSSpec (you have one or more tests that describe the behavior), YUI Test (testing framework for JavaScript), and Crosscheck (checks if your code runs in many different browsers).
If you are interested in testing your user interface, the article mentions some of the tools available, such as Selenium (set of tools that supports rapid development of test automation for web-based applications), Watir (an open-source library for automating web browsers), and YUI Test mentioned above which can also be used to simulate the DOM and user interaction.
Other utility tools for JavaScript include JSLint (JavaScript code quality tool), or JSMin ( removes comments and unnecessary whitespace from JavaScript files) and YUI Compressor (in addition to removing comments and whitespace, it also obfuscates local variables using the smallest possible variable name), for minimizing our JavaScript.
Since I have just started JavaScript, I cannot make any recommendations. Try them out, see which one fits your project best, and use it.
