I find it difficult to code in JavaScript when there are so many nested functions or objects within one another that it makes it difficult to modify your code without breaking it. What IDE can be used to expand and collapse code blocks (or lexical scope levels) within JavaScript source code, similar to how regions work in Visual Studio?
For old-fashioned IDE, try Eclipse: http://www.eclipse.org/downloads/packages/eclipse-ide-javascript-web-developers/heliosr
But I highly recommend using Sublime Text: http://www.sublimetext.com/
SublimeText doesn't collapse/expand, but it does display gutter lines to indicate how many tab indentations each block of code is. If you go to their site, look at the first demo slide, it shows the indentation of code blocks.