没有 if-else block 的 JavaScript 工厂模式

Question

我想知道是否有更好的方法来实现 createEmployee()，它使用字典或其他一些方法来快速查找所请求的类型，而不是 if-else block 。

function Clerk( options ) {
            this.hourRate = options.hourRate || 20;
            this.firstName = options.firstName || "no first name";
            this.lastName = options.lastName || "no last name";
            this.id = options.id || "-9999999999";
        }

        function Manager( options) {
            this.hourRate = options.hourRate || 200;
            this.firstName = options.firstName || "no first name";
            this.lastName = options.lastName || "no last name";
            this.id = options.id || "-9999999999";
            this.yearBonus = options.yearBonus || "200000";
        }

        function Teacher( options) {
            this.hourRate = options.hourRate || 100;
            this.firstName = options.firstName || "no first name";
            this.lastName = options.lastName || "no last name";
            this.id = options.id || "-9999999999";
            this.subject = options.subject || "history";
        }

        var EmployeesFactory = function() {};

        EmployeesFactory.prototype.createEmployee = function (options) {
            if(options.employeeType == "Clerk")
                employeeConstructor = Clerk;
            else if(options.employeeType == "Manager")
                employeeConstructor = Manager;
            else if(options.employeeType == "Teacher")
                employeeConstructor = Teacher;
            return new employeeConstructor(options);
        }

        var factory = new EmployeesFactory();
        var person = factory.createEmployee( {
            employeeType: "Manager",
            firstName: "Haim",
            lastName: "Michael",
            id: 234234234 } );

        document.write(person instanceof Manager);

Answer 1

试试这个:

var constructors;

constructors = {
    "Clerk" : function (options) {
        // your constructor code here for clerks
    },
    "Manager" : function (options) {
        // your constructor code here for managers
    },
    "Teacher" : function (options) {
        // your constructor code here for teachers
    }
};

EmployeesFactory.prototype.createEmployee = function (options) {
    return constructors[options.employeeType](options);
};

我建议将 constructors 对象很好地隐藏在 EmployeesFactory 中。通过这种方式，您还可以删除不需要的函数名称(Clerk、Manager 和 Teacher)。

此外，您应该只创建一次constructors 对象并在创建过程中重复使用它。不要在创建时实例化它。您可以通过以下方式执行此操作:

var EmployeesFactory = function () {
    var constructors;

    constructors = {
        "Clerk" : function (options) {
            // your constructor code here for clerks
        },
        "Manager" : function (options) {
            // your constructor code here for managers
        },
        "Teacher" : function (options) {
            // your constructor code here for teachers
        }
    };

    return {
        "create" : function (options) {
            return constructors[options.employeeType](options);
        }
    };
};

你可以这样得到工厂:

factory = EmployeesFactory();

并且可以这样创建东西:

factory.create(options);

所有东西都将舒适并隐藏在外层封闭内，没有内脏卡在外面。

工厂模式的目的是隐藏对象构建的复杂性和细节，因此将方法围绕用于消费在一个方面上遗漏了(我承认, minor/minimal) 的模式。通过使用闭包，您也可以获得隐藏的好处。