Object Oriented Programming in JavaScript

class.js

class Pet {
  constructor () {
  }
}

constructor.js

function Pet (name, born, died) {
  this.name = name
  this.born = born
  this.died = died
}

Pet.prototype.age = function () {
  return (this.died || new Date().getFullYear()) - this.born
}

function Dog (breed, name, born, died) {
  Pet.apply(this, [name, born, died])
  this.breed = breed
}

Dog.prototype = Object.create(Pet.prototype)

var dog = new Dog('Jim', 'Labrador', 1990, null)

object.js

var Pet = {
  init: function () {
    
  }
}

var Dog = {
  init: function (breed, options) {
    Pet.init.call(this, breed, options)
    this.breed = breed
  }
}