var model = (function(){
    var Car = (function(){
        var constractor = function Car(color){
            this.tireCount = 4;
            this.color = color;
            return this;
        };
        var p = constractor.prototype;
        p.getColor = function (){
            return this.color;
        };
        p.getTireCount = function (){
            return this.tireCount;
        };
        return constractor;
    })();

    var Truck = (function(){
        var constractor = function Truck(color, load){
            this.tireCount = 8;
            this.color = color;
            this.load = load;
            return this;
        };
        var p = constractor.prototype;
        Object.setPrototypeOf(p, Car.prototype); // 継承！

        p.getLoad = function (){
            return this.load;
        };
        return constractor;
    })();

    return {
        Car: Car,
        Truck: Truck
    };
})();

結果

>>> var car = new model.Car("red");
>>> console.log(car);
Car { tireCount: 4, color: 'red' }
>>> console.log(car.getColor());
red
>>> console.log(car.getTireCount());
4
>>> var truck = new model.Truck("blue", ["amazon", "amazon", "rakuten"]);
>>> console.log(truck);
Truck {
  tireCount: 8,
  color: 'blue',
  load: [ 'amazon', 'amazon', 'rakuten' ]
}
>>> console.log(truck.getColor());
blue
>>> console.log(truck.getTireCount());
8
>>> console.log(truck.getLoad());
[ 'amazon', 'amazon', 'rakuten' ]