为什么在超类中定义时在子类中使用 super(qualifications) 会抛出 ReferenceError？

Question

class SchoolEmployee {
  constructor(name, qualifications) {
    this._name = name;
    this._qualifications = qualifications;
    this._holidaysLeft = 21;
  }

  get name() {
    return this._name;
  }

  get qualifications() {
    return this._qualifications;
  }

  get holidaysLeft() {
    return this._holidaysLeft;
  }

  takeHolidays(days) {
    this._holidaysLeft -= days;
  }
}

class Teacher extends SchoolEmployee {
  constructor(name, qualifications, subject) {
    super(name);
    super(qualifications); //THIS IS THE ERROR
    this._subject = subject;
  }

  get name() {
    return this._name;
  }

  get qualifications() {
    return this._qualifications;
  }

  get subject() {
    return this._subject;
  }
}

let John = new Teacher('John', ['Maths', 'Physics'], 'Maths');

SchoolEmployee 是超级 class，我定义了 'qualifications' 是什么。据我所知，编写 super(qualifications) 会调用先前定义的 super class 的构造函数。目前我正在学习 Javascript，但我不明白哪里出了问题。有人可以帮助我吗？

Answer 1

如您所见，on mdn super() 调用了父级 class 的构造函数，并且您调用了它两次。你可能想要的是

class Teacher extends SchoolEmployee {
    constructor(name, qualifications, subject) {
        super(name, qualifications);
        this._subject = subject;
    }
}

Answer 2

SchoolEmployee 构造函数需要 2 个参数，您仅使用一个参数调用 super。尝试：

super(name, qualifications);

Answer 3

错误清楚地说 Super constructor may only be called once。 Super 调用构造函数并且作为父构造函数接受两个 name, qualifications 将它们传入一个 super.

class SchoolEmployee {
  constructor (name, qualifications) {
    this._name = name;
    this._qualifications = qualifications;
    this._holidaysLeft = 21;
  }

  get name() {
    return this._name;
  }

  get qualifications() {
    return this._qualifications;
  }

  get holidaysLeft() {
    return this._holidaysLeft;
  }

  takeHolidays(days) {
    this._holidaysLeft -= days;
  }
}

class Teacher extends SchoolEmployee {
  constructor (name, qualifications, subject) {
    super(name, qualifications);
    this._subject = subject;
  }

  get name() {
    return this._name;
  }

  get qualifications() {
    return this._qualifications;
  }

  get subject() {
    return this._subject;
  }
}

let John = new Teacher('John',['Maths', 'Physics'],'Maths');

为什么在超类中定义时在子类中使用 super(qualifications) 会抛出 ReferenceError？

Why does using super(qualifications) in a subclass throw a ReferenceError when it was defined in the superclass?

javascript

inheritance

subclass

superclass