While you don't need an IDE (Integrated Development Environment) per se, you will need a text editor. Why not have a text editor that does a little bit of the heavy lifting for you? There are, essentially, two types of IDEs available for JavaScript development. The first kind is really more of a text editor than anything else, whereas the second kind is a full-blown editor with compiling and source control built in.
While you can work on JavaScript with only a simple text editor and a console/Terminal window, we recommend using something with at least a little more power.