function alias(fname) {
    return function() {
        return this[fname].apply(this, arguments);
    };
};


function Animal() {};
Animal.prototype.sound = null;
Animal.prototype.animalSound = function() {
    return this.sound;
};


function Dog() {};
Dog.prototype = new Animal();
Dog.prototype.sound = 'bark';
Dog.protoype.bark = alias('animalSound');