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 helpervar 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();}