Human.js

var Human = new Class({ 
  initialize: function(name, age){
    this.name = name; 
    this.age = age;
  }, 
  isAlive: true, 
  energy: 1, 
  eat: function(){
    this.energy++;
  } 
});

// usage
var bob = new Human('Bob Ross', 50);
bob.energy; // 1, from the prototype
bob.eat(); // assigns bobs own energy to 2
bob.energy; // 2, prototype not checked anymore
bob.name; // Bob Ross, nothing to do with prototype