Наследование в цепочке прототипов

showDogs.js

function Dog(name, breed, weight) {
	this.name = name;
	this.breed = breed;
	this.weight = weight;
}

Dog.prototype.species = "Canine";
Dog.prototype.bark = function () {
	if (this.weight > 25) {
		console.log(this.name + " says Woof!");
	} else {
		console.log(this.name + " says Yip!");
	}
};

Dog.prototype.run = function () {
	console.log("Run!");
};
Dog.prototype.wag = function () {
	console.log("Wag!");
};
Dog.prototype.sitting = false;
Dog.prototype.sit = function (){
	if (this.sitting) {
		console.log(this.name + " is already sitting");
	} else {
		this.sitting=true;
		console.log(this.name + " is now sitting");
	}
};

function showDog(name, breed, weight, handler) {
	Dog.call(this, name, breed, weight);
	this.handler = handler;
}

showDog.prototype = new Dog();

//задаем конструктор ShowDog
showDog.prototype.constructor = showDog;

showDog.prototype.league="Webville";
showDog.prototype.stack = function () {
	console.log("Stack");
};
showDog.prototype.bait = function() {
	console.log("Bait");
};
showDog.prototype.gait = function(kind) {
	console.log(kind + "ing");
};
showDog.prototype.groom = function() {
	console.log("Groom");
};

var fido = new Dog("Fido", "Mixed", 38);
var fluffy = new Dog("Fluffy", "Poodle", 30);
var spot = new Dog("Spot", "Chihuahua", 10);
var scotty = new showDog("Scotty", "Scottish Terrier", 15, "Cookie");
var beatrice = new showDog("Beatrice", "Pomeranian", 5, "Hamilton");

fido.bark();
fluffy.bark();
spot.bark();
scotty.bark();
beatrice.bark();
scotty.gait("Walk");
beatrice.groom();