javascript - 从派生(ES2019 私有(private)类)访问基类的 protected 字段

Question

我想从派生类访问基类的私有(private)字段而不将它们公开(在其他语言中称为“ protected ”)。

考虑以下类:

class Animal {

  #privateProp;

  constructor() {

  this.#privateProp = 12;

  }
}

现在扩展类:

class Cat extends Animal {

  constructor() {

    super();
  }

  doIt() {

    console.log(this.#privateProp) // 1 below
    console.log(super.#privateProp) // 2 below
  }
}

我想像受到保护一样执行:

new Cat().doIt();

但是得到(分别):

1. Uncaught SyntaxError: Private field '#privateProp' must be declared in an enclosing class
2. Uncaught SyntaxError: Unexpected private field

请注意，当 privateProp 公开时，此代码将完美运行，但我想实现类似 protected 行为并像任何支持继承的语言一样访问“私有(private)”字段。

任何帮助将不胜感激。

Answer 1

you can create a private property with getter and setter methods having restricted access by checking if the constructor is not of the parent class itself.

class Animal {
  #privateProp = 12;
  set Prop(val) {
    if (this.constructor.name !== 'Animal')
      return this.#privateProp = val;
    throw new Error('Cannot Access Protected property');
  }
  get Prop() {
    if (this.constructor.name !== 'Animal')
      return this.#privateProp;
    throw new Error('Cannot Access Protected property');
  }
}

class Cat extends Animal {
  get Prop() {
    return super.Prop;
  }

  set Prop(val) {
    super.Prop = val
  }
}

let cat = new Cat();
console.log(cat.Prop)
cat.Prop = 22
console.log(cat.Prop)

console.log(new Animal().Prop);