Builder 模式 javascript

原文：http://www.dofactory.com/javascript-builder-pattern.aspx

function Shop() {
    this.construct = function(builder) {
        builder.step1();
        builder.step2();
        return builder.get();
    }
}

function CarBuilder() {
    this.car = null;
    this.step1 = function() {
        this.car = new Car();
    };
    this.step2 = function() {
        this.car.addParts();
    };
    this.get = function() {
        return this.car;
    };
}

function TruckBuilder() {
    this.truck = null;
    this.step1 = function() {
        this.truck = new Truck();
    };
    this.step2 = function() {
        this.truck.addParts();
    };
    this.get = function() {
        return this.truck;
    };
}

function Car() {
    this.doors = 0;
    this.addParts = function() {
        this.doors = 4;
    };
    this.say = function() {
        log.add("I am a " + this.doors + "-door car");
    };
}

function Truck() {
    this.doors = 0;
    this.addParts = function() {
        this.doors = 2;
    };
    this.say = function() {
        log.add("I am a " + this.doors + "-door truck");
    };
}

// log helper
var log = (function () {
    var log = "";
    return {
        add: function (msg) { log += msg + "\n"; },
        show: function () { alert(log); log = ""; }
    }
})();

function run() {
    var shop = new Shop();

    var carBuilder = new CarBuilder();
    var truckBuilder = new TruckBuilder();

    var car = shop.construct(carBuilder);
    var truck = shop.construct(truckBuilder);

    car.say();
    truck.say();

    log.show();
}