This method uses a flag (_initialized) to determine if the prototype has been assigned any methods yet.
The methods are only created and assigned once.
function Car(sColor, iDoors) {
this.color = sColor;
this.doors = iDoors;
this.drivers = new Array("A", "B");
if (typeof Car._initialized == "undefined") {
Car.prototype.showColor = function () {
alert(this.color);
};
Car._initialized = true;
}
}