Creating a method in prototype and calling it in Init

Question

I'm trying to create a module that I export and call from another file. My code is currently structured as it is below. When I call it from my main file, I get an error saying that my function, doSomething, does not exist. Is there a way to make this work? Should I be structuring my file differently or creating the instance of my object in the main file?

module.exports = function(){
    var my_class = function(a){
        this.init(a);
    }

    my_class.prototype = {
         doSomething: (g) => {
             // Doing something here
         }
         init: (b) () => {
              doSomething();
         }
    }

    return new my_class();
}