constructor.js

var cat = function(obj){
  //this is where I copy all the attributes of the passed object to the constructure
  for (attr in obj){
    this[attr] = obj[attr];
  }
  //publice method
  this.talk = function(){
    console.log('meeow!!!');
  };
};

//extend the class
cat.prototype.run = function(){
  console.log('running!!!');
};

//this can be locally defined, receive from user input or fetch from localstorage
var obj = {
  name : 'sona',
  age : 24,
  fav : {
    color : ['red'],
    number : [1, 2, 3]
  }
};
// recreate the object
var cat1 = new cat(obj);
cat1.talk();
cat1.run();
console.log(cat1);
var cat2 = new cat(obj);

//extend the class again
cat.prototype.walk = function(){
  console.log('walking');
};

//the new method is automatically avaiable to the new object although originally they were not defined.
cat2.walk();
cat1.walk();