Functional class of a dog object

dogFunctionalClass.js

var Dogs = function (name, breed, age, happiness, hunger, energy){
  var dog = {name : name, breed : breed, age : age, happiness : happiness, hunger : hunger, energy : energy};
  extend(dog, Dogs.methods)
  return dog;
}

Dogs.methods = {
  feed : function(food){
    if(this.hunger - food > 0) {
      this.hunger -= food;
    } else {
      this.hunger = 0;
    }
  },

  play : function(time){
    if(this.happiness + time < 100) {
      this.happiness += time;
    } else {
      this.happiness = 100;
    } 

    if(dog.energy - time > 0) {
      dog.energy -= time;
    } else {
      dog.energy = 0;
    }
  }, 

  nap : function(time) {
    if(this.energy + time < 100) {
      this.energy += time;
    } else {
      this.energy = 100;
    }
  }

}