Question

 <script>  
    var Employee = new function(name)
    {
     this.name=name;
    }
    Employee.prototype.getName = function()
    {
      return this.name;
    }

    var PermanenetEmployee = new function(annualsalary)
    {
    this.annualsalary=annualsalary;
    }
    var employee = new Employee("rahul");
    PermanenetEmployee.prototype = employee;
    var pe = new PermanenetEmployee(5001);
    document.write(pe.getName());



    </script>

我在java脚本中实现继承。从这段代码我想打印员工名称，如“rahul”。但我得到的错误就像Uncaught TypeError：无法设置未定义的属性'getName'（匿名函数）。如何解决此错误？

Employee.prototype.getName = function()
        {
          return this.name;
        }

Answer 1

这是问题所在：

var Employee = new function(name)
// ------------^^^
{
 this.name=name;
}

（PermanenetEmployee也一样。）

你不希望new在那里。 new 调用该函数。您希望稍后这样做，就像分配给employee时一样。

请注意，您在它们之间设置继承的方式是反模式。要使PermanenetEmployee正确“子类化”Employee，请执行以下操作：

PermanenetEmployee.prototype = Object.create(Employee.prototype);
PermanenetEmployee.prototype.constructor = PermanenetEmployee;

不

var employee = new Employee("rahul");
PermanenetEmployee.prototype = employee;

...然后PermanenetEmployee接受name并将其传递给Employee：

var PermanenetEmployee = function(name, annualsalary) {
    Employee.all(this, name); // <====
    // ...
};

...或更好地使用，使用ES2015（“ES6”）class（如果你需要，例如使用Babel进行转换）。

这是一个正确的设置。我还在PermanenetEmployee中修正了拼写错误：

var Employee = function(name) {
    this.name = name;
};
Employee.prototype.getName = function() {
    return this.name;
};

var PermanentEmployee = function(name, annualSalary) {
    Employee.call(this, name);
    this.annualSalary = annualSalary;
};

// Set up subclass
PermanentEmployee.prototype = Object.create(Employee.prototype);
PermanentEmployee.prototype.constructor = PermanentEmployee.prototype;

PermanentEmployee.prototype.getAnnualSalary = function() {
    return this.annualSalary;
};

// Using
var pe = new PermanentEmployee("Rahul", 5001);
console.log(pe.getName());
console.log(pe.getAnnualSalary());

使用ES2015：

class Employee {
    constructor(name) {
        this.name = name;
    }
    getName() {
        return this.name;
    }
}

class PermanentEmployee extends Employee {
    constructor(name, annualSalary) {
        super(name);
        this.annualSalary = annualSalary;
    }

    getAnnualSalary() {
        return this.annualSalary;
    }
}

// Using
var pe = new PermanentEmployee("Rahul", 5001);
console.log(pe.getName());
console.log(pe.getAnnualSalary());

同样，请注意，如果要在野外使用该语法（现在），则需要进行转换。

Answer 2

有几种方法可以让你继续在JS中工作，我正在使用这种模式。

首先声明基础原型：

Employee = function () {
};
Employee.prototype = {
    getName: function () {}
};

然后继承基础的原型：

PermanentEmployee = function () {
    Employee.call(this);
};

PermanentEmployee.prototype = Object.create(Employee.prototype);
PermanentEmployee.constructor = PermanentEmployee;

PermanentEmployee.prototype.foo = function() {}

未捕获的TypeError：无法设置未定义的属性'getName'（匿名函数）

2 个答案: