function Animal() {

  this.__getName = function () {

    return String(this.constructor.name);

  };

  this.species = function (term) {

    console.log('Animal species: ' + this.__getName());

  };

}

​

function Cat() {}

Cat.prototype = new Animal();

Cat.prototype.constructor = Cat;

var cat = new Cat();

cat.species();

​

function Dog() {}

Dog.prototype = new Animal();

Dog.prototype.constructor = Dog;

var dog = new Dog();

dog.species();

​

Animal.prototype.__move = function (movement) {

  console.log('The ' + this.__getName() + ' ' + movement + '!');

};

​

Cat.prototype.walk = function () {

  this.__move('walked');

};

cat.walk();

​

Dog.prototype.run = function () {

  this.__move('ran');

};

dog.run();

​

function Fish() {}

Fish.prototype = new Animal();

Fish.prototype.constructor = Fish;

var fish = new Fish();

fish.species();

​

Fish.prototype.swim = function () {

  this.__move('swam');

};

fish.swim();