Object.prototype.extend

gistfile1.js

Object.prototype.extend = function (object) {
  var Constructor = object.initialize;

  Constructor.prototype = Object.create(this.prototype);

  Object.keys(object).forEach(function (key) {
    if (key !== "initialize") {
      Constructor.prototype[key] = object[key];
    }
  });

  Constructor.prototype.constructor = object.initialize;

  return Constructor;
};

var Animal = Object.extend({
  initialize: function (species) {
    this.species = species;
  },

  walk: function () {
    return "I'm walking!";
  }
});

var Human = Animal.extend({
  initialize: function (name, age) {
    Animal.prototype.constructor.call(this, "Human"); // Call to super.

    this.name = name;
    this.age = age;
  },

  talk: function () {
    return "My name is " + this.name + "!";
  }
});

var human = new Human("Dennis", 31);

console.log(human instanceof Animal); // Returns true.
console.log(human instanceof Human); // Returns true.