function Vehicle(make, model, year) {
  this.make = make;
  this.model = model;
  this.year = year;
}

Vehicle.prototype.wheels =4;
Object.defineProperty(Vehicle.prototype,"wheels",{writable:false});

var audi_a3 = new Vehicle("Audi","A3","2008");
var bmw_s_1000_rr = new Vehicle("BMW","S 1000 RR", "2009");

audi_a3.wheels=4;
bmw_s_1000_rr.wheels=2;

Object.defineProperty(Vehicle.prototype,"wheels",{writable:true});
bmw_s_1000_rr.wheels = 2;
console.log("Audi has "+audi_a3.wheels+" wheels");
//Vehicle.prototype.wheels = 2;
console.log("Audi has "+audi_a3.wheels+" wheels");