Edit in JSFiddle

function Animal(species, alive, age) {
    this.species = species;
    this.alive = alive;
    this.age = age;
}

function Dog(alive, age, likesCats) {
    Animal.call(this, "Dog", alive, age);
    
    this.likesCats = likesCats;
}

Dog.prototype = Object.create(Animal.prototype);
Dog.prototype.constructor = Dog;

function Cat(alive, age, likesDogs) {
    Animal.call(this, "Cat", alive, age);
    
    this.likesDogs = likesDogs;
}

Cat.prototype = Object.create(Animal.prototype);
Cat.prototype.constructor = Cat;

var spike = new Dog(true, 2, true);
var fluffy = new Cat(true, 0.5, true);

// Let's check out what we have...
log(spike);
log(fluffy);

if(spike.likesCats && fluffy.likesDogs) {
	log("Fluffy and Spike like each other");
} else {
	log("Fluffy and Spike don't get along");
}
    
log("Spike is " + spike.age + " years old.");

log("Fluffy is a " + fluffy.species + ".");

<div id="log"></div>