如何使用call()进行继承.错误:如果没有"new"，则无法调用类构造函数 [英] How to use call() for inheritance. Error: Class constructor cannot be invoked without 'new'

问题描述

您能解释一下使用 class 时如何实现继承吗?

Can you explain me how to implement inheritance when using class?

当我使用 function 定义构造函数时，一切正常(参见代码版本1).但是，当我将 function 转换为ES2015 class (版本2)时，会产生以下错误:

When I use function for defining the constructor, everything works (cf. code version 1). But when I turn function into an ES2015 class (version 2) it produces this error:

未捕获的TypeError:类构造函数无法在没有'new'的情况下调用Person

Uncaught TypeError: Class constructor Person cannot be invoked without 'new'

我是否需要在代码中添加一些内容，还是应该使用 function 使其保持原样?

Do I need to add something to the code or should I just leave it as it is with function?

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

function Customer(firstName, lastName, phone, membership) {
  Person.call(this, firstName, lastName);
  this.phone = phone;
  this.membership = membership;
}

const customer1 = new Customer("Tom", "Smith", "555-555-555", "Standard");
console.log(customer1);

class Person {
  constructor(firstName, lastName) {
    this.firstName = firstName;
    this.lastName = lastName;
  }
}

class Customer {
  constructor(firstName, lastName, phone, membership) {
    Person.call(this, firstName, lastName); // <--- TypeError
    this.phone = phone;
    this.membership = membership;
  }
}

const cust1 = new Customer("Bob", "Johnes", "555-222-333", "Silver");
console.log(cust1);

推荐答案

实际上，当 Person 用<代码>类.ES2015提供了 extends 和 super 关键字来实现原型链定义:

Indeed, it is not allowed to do Person.call() when Person is defined with class. ES2015 offers the extends and super keywords for achieving such prototype-chain definition:

class Customer extends Person {
  constructor(firstName, lastName, phone, membership) {
    super(firstName, lastName);
    this.phone = phone;
    this.membership = membership;
  }
}

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