Javascript中Factory的应用

    这里拿Pro Javascript Design Pattern中的例子作为case。假如一家自行车店销售各种自行车： 

/* The Bicycle interface. */
var Bicycle = new Interface("Bicycle", ["assemble", "wash", "ride", "repair"]);

/* Speedster class. */
var Speedster = function () { }
Speedster.prototype = {
    assemble: function () {
        console.log("Speedster Bicycle assembled.");
    },
    wash: function () {
        console.log("Speedster Bicycle washed.");
    },
    ride: function () {
        console.log("Speedster Bicycle ride.");
    },
    repair: function () {
        console.log("Speedster Bicycle repaired.");
    }
};
Speedster.prototype.constructor = Speedster;

/* Lowrider class. */
var Lowrider = function () { }
Lowrider.prototype = {
    assemble: function () {
        console.log("Lowrider Bicycle assembled.");
    },
    wash: function () {
        console.log("Lowrider Bicycle washed.");
    },
    ride: function () {
        console.log("Lowrider Bicycle ride.");
    },
    repair: function () {
        console.log("Lowrider Bicycle repaired.");
    }
};
Lowrider.prototype.constructor = Lowrider;

/* ComfortCruiser class. */
var ComfortCruiser = function () { }
ComfortCruiser.prototype = {
    assemble: function () {
        console.log("ComfortCruiser Bicycle assembled.");
    },
    wash: function () {
        console.log("ComfortCruiser Bicycle washed.");
    },
    ride: function () {
        console.log("ComfortCruiser Bicycle ride.");
    },
    repair: function () {
        console.log("ComfortCruiser Bicycle repaired.");
    }
};
ComfortCruiser.prototype.constructor = ComfortCruiser;

/* BicycleShop class. */
var BicycleShop = function () { };
BicycleShop.prototype = {
    sellBicycle: function (model) {
        var bicycle;
        switch (model) {
            case "The Speedster":
                bicycle = new Speedster();
                break;
            case "The Lowrider":
                bicycle = new Lowrider();
                break;
            case "The Comfort Cruiser":
            default:
                bicycle = new ComfortCruiser();
                break;
        }

        Interface.ensureImplements(bicycle, [Bicycle]);
        bicycle.assemble();
        bicycle.wash();

        return bicycle;
    }
};
BicycleShop.prototype.constructor = BicycleShop;

/* test */
(function () {
    var bicycle = new BicycleShop().sellBicycle("The Lowrider");
    bicycle.ride();
    bicycle.repair();

})(); 

其中，

Bicycle为自行车接口，之后3个类为类型的自行车，在BicycleShop的SellBicycle中是先根据条件创建具体自行车型，然后组装清洗。 

    改进第一步是将上述SellBicycle方法利用Simple Factory进行改进： 

/* Bicycle Factory */
var BicycleFactory = {
    createBicycle: function (model) {
        var bicycle;
        switch (model) {
            case "The Speedster":
                bicycle = new Speedster();
                break;
            case "The Lowrider":
                bicycle = new Lowrider();
                break;
            case "The Comfort Cruiser":
            default:
                bicycle = new ComfortCruiser();
                break;
        }
        Interface.ensureImplements(bicycle, [Bicycle]);

        return bicycle;
    }
};

/* BicycleShop class. */
var BicycleShop = function () { };
BicycleShop.prototype = {
    sellBicycle: function (model) {
        var bicycle = BicycleFactory.createBicycle(model);
        bicycle.assemble();
        bicycle.wash();

        return bicycle;
    }
};

BicycleShop.prototype.constructor = BicycleShop; 

可以看到，多了一个Bicycle构造工厂， BicycleShop的职责只负责组装和清洗了。 当增加了新的车型，只需要更新BicycleFactory，不需要修改BicycleShop。

      好，当车型比较少时完全可以满足需要。但是，当车店需要区分品牌和车型时就不行了。我们继续，利用Factory Method来进行改进。因为改动较大，贴出完整代码如下： 

/* The Bicycle interface. */
var Bicycle = new Interface("Bicycle", ["assemble", "wash", "ride", "repair"]);

/* Acme Speedster class. */
var AcmeSpeedster = function () { }
AcmeSpeedster.prototype = {
    assemble: function () {
        console.log("Acme Speedster Bicycle assembled.");
    },
    wash: function () {
        console.log("Acme Speedster Bicycle washed.");
    },
    ride: function () {
        console.log("Acme Speedster Bicycle ride.");
    },
    repair: function () {
        console.log("Acme Speedster Bicycle repaired.");
    }
};
AcmeSpeedster.prototype.constructor = AcmeSpeedster;

/* Acme Lowrider class. */
var AcmeLowrider = function () { }
AcmeLowrider.prototype = {
    assemble: function () {
        console.log("Acme Lowrider Bicycle assembled.");
    },
    wash: function () {
        console.log("Acme Lowrider Bicycle washed.");
    },
    ride: function () {
        console.log("Acme Lowrider Bicycle ride.");
    },
    repair: function () {
        console.log("Acme Lowrider Bicycle repaired.");
    }
};
AcmeLowrider.prototype.constructor = AcmeLowrider;

/* Acme ComfortCruiser class. */
var AcmeComfortCruiser = function () { }
AcmeComfortCruiser.prototype = {
    assemble: function () {
        console.log("Acme ComfortCruiser Bicycle assembled.");
    },
    wash: function () {
        console.log("Acme ComfortCruiser Bicycle washed.");
    },
    ride: function () {
        console.log("Acme ComfortCruiser Bicycle ride.");
    },
    repair: function () {
        console.log("Acme ComfortCruiser Bicycle repaired.");
    }
};
AcmeComfortCruiser.prototype.constructor = AcmeComfortCruiser;


/* General Speedster class. */
var GeneralSpeedster = function () { }
GeneralSpeedster.prototype = {
    assemble: function () {
        console.log("General Speedster Bicycle assembled.");
    },
    wash: function () {
        console.log("General Speedster Bicycle washed.");
    },
    ride: function () {
        console.log("General Speedster Bicycle ride.");
    },
    repair: function () {
        console.log("General Speedster Bicycle repaired.");
    }
};
GeneralSpeedster.prototype.constructor = GeneralSpeedster;

/* General Lowrider class. */
var GeneralLowrider = function () { }
GeneralLowrider.prototype = {
    assemble: function () {
        console.log("General Lowrider Bicycle assembled.");
    },
    wash: function () {
        console.log("General Lowrider Bicycle washed.");
    },
    ride: function () {
        console.log("General Lowrider Bicycle ride.");
    },
    repair: function () {
        console.log("General Lowrider Bicycle repaired.");
    }
};
GeneralLowrider.prototype.constructor = GeneralLowrider;

/* General ComfortCruiser class. */
var GeneralComfortCruiser = function () { }
GeneralComfortCruiser.prototype = {
    assemble: function () {
        console.log("General ComfortCruiser Bicycle assembled.");
    },
    wash: function () {
        console.log("General ComfortCruiser Bicycle washed.");
    },
    ride: function () {
        console.log("General ComfortCruiser Bicycle ride.");
    },
    repair: function () {
        console.log("General ComfortCruiser Bicycle repaired.");
    }
};
GeneralComfortCruiser.prototype.constructor = GeneralComfortCruiser;


/* BicycleShop class. */
var BicycleShop = function () { };
BicycleShop.prototype = {
    sellBicycle: function (model) {
        var bicycle = this.createBicycle(model);
        bicycle.assemble();
        bicycle.wash();

        return bicycle;
    },
    createBicycle: function (model) {
        throw new Error("BicycleShop is abstract, not implements createBicycle.");
    }
};
BicycleShop.prototype.constructor = BicycleShop;

/* Acme Bicycle Shop */
var AcmeBicycleShop = function () { };
extend(AcmeBicycleShop, BicycleShop);
AcmeBicycleShop.prototype.createBicycle = function (model) {
    var bicycle;
    switch (model) {
        case "The Speedster":
            bicycle = new AcmeSpeedster();
            break;
        case "The Lowrider":
            bicycle = new AcmeLowrider();
            break;
        case "The Comfort Cruiser":
        default:
            bicycle = new AcmeComfortCruiser();
            break;
    }
    Interface.ensureImplements(bicycle, [Bicycle]);

    return bicycle;
};


/* General Bicycle Shop */
var GeneralBicycleShop = function () { };
extend(GeneralBicycleShop, BicycleShop);
GeneralBicycleShop.prototype.createBicycle = function (model) {
    var bicycle;
    switch (model) {
        case "The Speedster":
            bicycle = new GeneralSpeedster();
            break;
        case "The Lowrider":
            bicycle = new GeneralLowrider();
            break;
        case "The Comfort Cruiser":
        default:
            bicycle = new GeneralComfortCruiser();
            break;
    }
    Interface.ensureImplements(bicycle, [Bicycle]);

    return bicycle;
};


/* test */
(function () {
    var bicycle = new GeneralBicycleShop().sellBicycle("The Lowrider");
    bicycle.ride();
    bicycle.repair();

})();  

重点在于，我们将

BicycleShop变更为一个抽象类，即将CreateBicycle()方法作为抽象方法。然后，

AcmeBicycleShop 和 

GeneralBicycleShop作为2个品牌的自行车店均继承于它，各自实现CreateBicycle()方法。

另外，附件还附有2个例子，download