Question

我希望能够在使用原型创建对象时为变量指定默认值。

当我尝试为变量指定默认值时，它们总是“未定义”。

我试图找到答案，但我尝试过的所有可能的解决办法都没有用。

我的问题是：

为什么我使用值启动的变量具有值＆＃39; undefined＆＃39;

如何解决我的问题？

(function() {
    EmployeeNS = {};

    EmployeeNS.Employee =   function() {
                                var _firstName;
                                var _lastName;
                                var _employeeID = 'Unassigned';
                            }
    EmployeeNS.Employee.prototype.setFirstName = function(fName) { this._firstName = fName; };
    EmployeeNS.Employee.prototype.getFirstName = function() { return this._firstName; };
    EmployeeNS.Employee.prototype.setLastName = function(lName) { this._lastName = lName; };
    EmployeeNS.Employee.prototype.getLastName = function() { return this._lastName; };
    EmployeeNS.Employee.prototype.setEmployeeID = function(employeeID) { this._employeeID = employeeID; };
    EmployeeNS.Employee.prototype.getEmployeeID = function() { return this._employeeID; };

    EmployeeNS.Worker = function() {
        var _department;
    }
    EmployeeNS.Worker.prototype = new EmployeeNS.Employee();
    EmployeeNS.Worker.prototype.constructor = Worker;
    EmployeeNS.Worker.prototype.setDepartment = function(department) { this._department = department; };
    EmployeeNS.Worker.prototype.getDepartment = function() { return this._department; };

})();

function createWorker() {
    var x = new EmployeeNS.Worker();
    x.setFirstName("John");
    x.setLastName("Doe");
    x.setDepartment("Transport");

    var message = x.getFirstName() 
                  + " " 
                  + x.getLastName()  
                  + " (Department: " 
                  + x.getDepartment()
                  + " / EmployeeID: " 
                  + x.getEmployeeID()
                  + ")";
    alert(message);
}

由于

Answer 1

你可以通过改变这样来简单地使它工作，

  EmployeeNS.Employee =   function() {
                            this._firstName;
                            this._lastName;
                            this._employeeID = 'Unassigned';
   }

尝试这种方式，您可以通过包装Employee，

使这些变量真正变为私有

(function() {
    EmployeeNS = {};

    (function() {
           var _firstName;
                                var _lastName;
                                var _employeeID = 'Unassigned';
    EmployeeNS.Employee =   function() {

                            }
    EmployeeNS.Employee.prototype.setFirstName = function(fName) { _firstName = fName; };
    EmployeeNS.Employee.prototype.getFirstName = function() { return _firstName; };
    EmployeeNS.Employee.prototype.setLastName = function(lName) { _lastName = lName; };
    EmployeeNS.Employee.prototype.getLastName = function() { return _lastName; };
    EmployeeNS.Employee.prototype.setEmployeeID = function(employeeID) { _employeeID = employeeID; };
    EmployeeNS.Employee.prototype.getEmployeeID = function() { return _employeeID; };

    })();

    (function() {
      var _department;        
     EmployeeNS.Worker = function() {

    }
    EmployeeNS.Worker.prototype = new EmployeeNS.Employee();
    EmployeeNS.Worker.prototype.constructor = Worker;
    EmployeeNS.Worker.prototype.setDepartment = function(department) { _department = department; };
    EmployeeNS.Worker.prototype.getDepartment = function() { return _department; };
    })();
})();

以下是jsfiddle

Answer 2

如果您想要实例属性，请执行以下操作：

(function() {
    EmployeeNS = {};
    EmployeeNS.Employee = function () {
        this._firstName = null;
        this._lastName = null;
        this._employeeID = 'Unassigned';
    };
    EmployeeNS.Employee.prototype.setFirstName = function(fName) { 
        this._firstName = fName; 
    };
})();

使用原型设计为javascript分配默认值

2 个答案: