Hoy un método rápido para simular herencia en Javascript.

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

Y cómo lo usamos:

var Animal = (function () {
  var Clazz = function () {
    this.name = "Animal";
  };
  var p = extend(Clazz, Object);
  p.run = function () {
    console.log(this.name + " running.");
  };
  return Clazz;
})();

var Dog = (function () {
  var Clazz = function () {
    this.name = "Dog";
  };
  extend(Clazz, Animal);
  return Clazz;
})();

var cat = new Animal();
cat.run(); // "Animal runnning"

var dog = new Dog();
dog.run(); // "Dog runnning"