javascript - 构造函数中Object.defineProperty的获取中的"undefined"

Question

我无法理解我在显示firstName 和lastName 方法的当前值的方式上犯了什么错误。现在，我在 jone.Name 和 jone.last 中遇到错误，因为它们得到 - 未定义。

function User(fullName) {
  this.fullName = fullName.split(' ');

  Object.defineProperty(this, 'firstName', {
    get: function() {
        this.firstName = this.fullName[0];
        return this.firstName;
    }
  });

  Object.defineProperty(this, 'lastName', {
    get: function() {
        this.lastName = this.fullName[1];
        return this.lastName;
    }   
  });

}

var jone= new User("Jone Coven");

console.log(jone.fullName);
console.log(jone.firstName);
console.log(jone.lastName);

Answer 1

问题在于 this.firstName = ... 和 this.lastName = ... 覆盖已使用 Object.defineProperty 定义的属性(这个，...).

这是一个使用附加私有(private)属性 this._firstName 和 this._lastName 的固定版本:

function User(fullName) {
  this.fullName = fullName.split(' ');

  Object.defineProperty(this, 'firstName', {
    get: function() {
        this._firstName = this.fullName[0]; // <------ _firstName
        return this._firstName;
    }
  });

  Object.defineProperty(this, 'lastName', {
    get: function() {
        this._lastName = this.fullName[1]; // <----- _lastName
        return this._lastName;
    }   
  });

}

var jone= new User("Jone Coven");

console.log(jone.fullName);
console.log(jone.firstName);
console.log(jone.lastName);

<小时/>

另一种解决方案是立即返回结果:

function User(fullName) {
  this.fullName = fullName.split(' ');

  Object.defineProperty(this, 'firstName', {
    get: function() {
        return this.fullName[0];
    }
  });

  Object.defineProperty(this, 'lastName', {
    get: function() {
        return this.fullName[1];
    }   
  });

}

var jone= new User("Jone Coven");

console.log(jone.fullName);
console.log(jone.firstName);
console.log(jone.lastName);

<小时/>