Isolating the inheritance part into a function

Let's move the code that takes care of all the inheritance details from the last example into a reusable extend() function:

    function extend(Child, Parent) { 
    var F = function () {}; 
    F.prototype = Parent.prototype; 
    Child.prototype = new F(); 
    Child.prototype.constructor = Child; 
    Child.uber = Parent.prototype; 
    } 

Using this function (or your own custom version of it) helps you keep your code clean with regard to the repetitive inheritance-related tasks. This way, you can inherit by simply using the following two lines of code:

    extend(TwoDShape, Shape); 
    extend(Triangle, TwoDShape); 

Let's see a complete example:

    // inheritance helper 
    function extend(Child, Parent) { 
      var F = function () {}; 
      F.prototype = Parent.prototype; 
      Child.prototype = new F(); 
      Child.prototype.constructor = Child; 
      Child...