test

var foodType = {fish: 0, bones: 1}

function Animal()
{
    var foodTypeForEating;

    this.Eat = function(foodType) {foodTypeForEating = foodType;}

    this.SaySomething = function(typicalFoodOfAnimal)    
    {
        if (typeof(foodTypeForEating) == "undefined" || foodTypeForEating == null) 
        {
            console.log("Nothing to eat...");
        }
        else 
        {
            if (foodTypeForEating == typicalFoodOfAnimal)
            {
                console.log("It's very tasty...");
            }
            else
            {
                console.log("I will not eat it...");
            }
        }
    }
}

var Cat = function()
{
    var typicalFoodOfCats = foodType.fish;
    
    this.__proto__ = new Animal();
    
    this.SaySomething = function() {this.__proto__.SaySomething(typicalFoodOfCats);}
}

var Dog = function()
{
    var typicalFoodOfDogs = foodType.bones;
    
    this.__proto__ = new Animal();
    
    this.SaySomething = function() {this.__proto__.SaySomething(typicalFoodOfDogs);}
}

var cat = new Cat();
var dog = new Dog();

cat.Eat(foodType.fish);
dog.Eat(foodType.fish);
cat.SaySomething();
dog.SaySomething();

var animal = new Animal();
animal.Eat(foodType.fish)
animal.SaySomething(foodType.fish);