After a good read though Javascript: The Good Parts , and the start of a rather large class that I’ll be writing in my spare time, I thought of how I could setup private variables in a Mootools class. YUI’s Module pattern is an easy way to make some private variables, but it needed to fit into the Mootools Class pattern. So I merged the two ideas, and created a Class Mutator, that lets you define a Privates object, and you get private variables!