Question

我正在尝试学习如何使用Object.defineProperties（）。我使用以下代码：

var Person = function(firstName, lastName)
{
    this.firstName = firstName;
    this.lastName = lastName;
};

Object.defineProperties(Person, {
    sayHi : {
        get : function() {return "Hello";},
        enumerable : true
    },
    sayBye : {
        get : function() {return "Bye";},
        enumerable : true
    }
});


var john = new Person('John', 'Doe');
console.log(john.sayHi());

但我一直在接受：

TypeError: john.sayHi is not a function
console.log(john.sayHi());

有人可以告诉我这段代码有什么问题吗？

由于

Answer 1

好吧，你没有将sayHi定义为一个函数。这是如何将其定义为函数：

var Person = function(firstName, lastName)
{
    this.firstName = firstName;
    this.lastName = lastName;
};
// Define the properties on the prototype, not the Person object itself
Object.defineProperties(Person.prototype, {
    sayHi : {
        get : function() {
          return function() {
            return "Hello, I am " + this.firstName + " " + this.lastName;
          };
        },
        enumerable : true
    },
    sayBye : {
        get : function() {
          return function() {
            return "Bye";
          };
        },
        enumerable : true
    }
});

var john = new Person('John', 'Doe');
console.log(john.sayHi());
console.log(john.sayBye());

准确地说：在你的代码中，john.sayHi返回＆＃34; Hello＆＃34; string，这是一个字符串原语，因此绝对不是函数; - ）

属性的get函数必须返回一个函数才能达到你想要的效果。

为了给你一个更长的答案，请看下面的其他实现，充分利用两件事：首先是ES5（Object.create()）和ES6（Object.defineProperties()）的新功能和原型性质JS（不使用new运算符，原型继承）：

var Person = {
    init: function(firstName, lastName) {
        this.firstName = firstName;
        this.lastName = lastName;
    }
};

Object.defineProperties(Person, {
    sayHi : {
        get : function() {return function() {return "Hello, I am " + this.firstName + " " + this.lastName;}},
        enumerable : true
    },
    sayBye : {
        get : function() {return function() {return "Bye";};},
        enumerable : true
    }
});

var Employee = Object.create(Person); // Employee inherits from Person

Employee.init = function(firstName, lastName, position) {
    this.firstName = firstName;
    this.lastName = lastName;
    this.position = position;
};

Object.defineProperties(Employee, {
    introduce : {
        get : function() {return function() {
            return this.sayHi() + ", " + this.position;
        }},
        enumerable : true
    },
    farewell : {
        get: function() {return function() {
            return this.sayBye() + ", it was a pleasure to meet you";
        }},
        enumerable: true
    }
});

var john = Object.create(Employee); // john inherits from Employee
john.init('John', 'Doe', 'Manager');

console.log(john.sayHi()); // Inherited from Person
console.log(john.introduce()); // Inherited from Employee
console.log(john.sayBye()); // Inherited from Person
console.log(john.farewell()); // Inherited from Employee

JSFIddle demo

Answer 2

替换

get : function() {return "Hello";}   with

get : function() {return function() {return "Hello";};}

JavaScript：使用Object.defineProperties（）

2 个答案: