Javascript "abstract method"

My terminology is a bit off, so feel free to correct where necessary. I want to overload a function in javascript and the 'base class' to make use of the overloaded method as well as the inherited class to access the base classes methods. So far, I came up with a (working) mix of jquery.extend() and object literals, but this doesn't look pretty. I was wondering if there's a better way of doing this (can use jquery).

var Base = new function(args, m) {
   $.extend(this, m);
   var self = this;
   this.bar = function() {
     self.foo();
   }
   this.foo = function() {
     self.blah();
   }
   this.dosomething = function() {}
};

var Child = function(arg1) {
   $.extend(this, new Base(args, {
     blah: function() {
       self.dosomething()
     }
   }));
}