Javascript Class Inheritance For Functions

I have set up a base class as standard:

MyBase = function() {
    this.m_Stuff = 0; // etc
};
MyBase.prototype.MySuperFunction = function (arg1) {
    alert("Hello" + arg1);
};

Next I set up another class that inherits MyBase

MyChild = function () {
    MyBase.call(this);
    this.m_OtherStuff = 1; // etc
};
MyChild.prototype = new MyBase(); // innherit

But then (and this is the bit I dont know how to do) I want to override MyBase's MySuperFunction with a better one, but calling the base class function in the process:

MyChild.prototype.MySuperFunction = function (arg1, arg2) {
    MyBase.MySuperFunction(arg1); // THIS LINE IS THE LINE I DONT KNOW HOW TO DO
    alert("You is a " + arg2 + "'th level idiot");
};

Its a child class that wants to override is base class function, but wants to call the base class function in the new improved definition.

Is this possible, and if so, how can it be done?

It's similar to the call in your inherited constructor. You can access the "super" method still on MyBase.prototype.MySuperFunction (where you assigned it), so use:

MyBase.prototype.MySuperFunction.call(this, arg1);

For a more dynamic approach you even might use Object.getPrototypeOf to get the prototype, but watch out that it works with dynamic inheritance. And if you have many methods that need to call their parent, it can be helpful to alias MyBase.prototype as a super variable which is accessible to all functions on the Child prototype object (see this answer for an example)).

Please apply the following:-

MyBase.prototype.MySuperFunction.call(this, arg1);