JavaScript at OSX

If you are looking for the JavaScript environment
1. JavaScript interpreter in OSX

/System/Library/Frameworks/JavaScriptCore.framework/Resources/jsc

And you can simply call the following code

// test.js
var test = 1
print('Hello ' + test)

very simply by calling

/System/Library/Frameworks/JavaScriptCore.framework/Resources/jsc test.js

2. Install NetBeans :)

In NetBeans 4, create HTML5 project, create JavaScript file, create HTML file that uses this file and you have full debugging support.