js工厂模式

//父构造器
function CarMaker(){}
//在原型中添加共享的方法
CarMaker.prototype.drive = function(){
    return "Vroom, I have "+ this.doors + " doors";
};
//静态工厂方法
CarMaker.factory = function(type){
    var constr = type,
        newcar;
    //如果构造函数不存在，则发生错误
    if(typeof CarMaker[constr] !== "function"){
        throw {
            name:"error",
            message:constr + " doesn‘t exit"
        };
    }
    //使得原型继承父类，仅继承了一次
    if(typeof CarMaker[constr].prototype.drive !== "function"){
        CarMaker[constr].prototype = new CarMaker();
    }
    //创建一个实例
    newcar = new CarMaker[constr]();
    return newcar;
};
//定义特定的汽车构造商
CarMaker.Compact = function(){
    this.doors = 4;
};
CarMaker.Convertible = function(){
    this.doors = 1;
};
CarMaker.SUV = function(){
    this.doors = 17;
};
//test
var compact = CarMaker.factory("Compact");
var convertible = CarMaker.factory("Convertible");
var suv = CarMaker.factory("SUV");
console.log(compact.drive()); //Vroom, I have 4 doors
console.log(convertible.drive()); //Vroom, I have 1 doors
console.log(suv.drive()); //Vroom, I have 17 doors