Javascriptのオブジェクトにprototypeで柔軟に属性をつける

var garage = [];

var Car = function (color, price){
  this.color = color;
  this.price = price;
  return this;
}


// 伝えたいところはココ
Car.prototype.isNew = function (){
  this.isNew = true;
  return this;
};

var old_car = new Car("red", 10000000);
garage.push(old_car);

var new_car = new Car("blue", 100000000).isNew();
garage.push(new_car);


function searchNewCarsFromGarage (){
  var new_cars = [];
  for ( car_num in garage ){
    if (garage[car_num]. hasOwnProperty("isNew")){
      new_cars.push(garage[car_num]);
    }
  return new_cars;
}