JavaScript 来自 class 扩展的函数无法识别

Question

我正在玩 classes ES6，遇到了以下代码的行为。

我得到的错误是 bob.personName is not a function。

class 和它的扩展都定义了 constructor 但我仍然无法让它工作。我在我认为可能是问题所在的行下添加了评论。感谢您的帮助！

class Person {
  constructor(canSpeak) {
    this.canSpeak = true;
  }
}

class Hello extends Person {
  constructor(name) {
  this.name = name;
  }

  personName() { //am I missing a parameter?
    if (this.canSpeak) {
      return `Name is: ${this.name}, can speak? ${this.canSpeak}`;
        }
    };
};

const bob = new Person('Bob'); //should I call Hello extension instead?
console.log(bob.personName());

Answer 1

由于方法存在于 Hello.prototype，而不存在于 Person.prototype，您需要实例属于 Hello.

您也不能引用 this，直到在子类的构造函数中调用 super，所以在分配给 this.name:

之前这样做

class Person {
  constructor(canSpeak) {
    this.canSpeak = true;
  }
}

class Hello extends Person {
  constructor(name) {
    super();
    this.name = name;
  }

  personName() { //am I missing a parameter?
    if (this.canSpeak) {
      return `Name is: ${this.name}, can speak? ${this.canSpeak}`;
    }
  };
};

const bob = new Hello('Bob'); //should I call Hello extension instead?
console.log(bob.personName());

JavaScript 来自 class 扩展的函数无法识别

JavaScript function from class extension not recognized

javascript

ecmascript-6

es6-class