从派生类(ES2019 私有类)访问基类的受保护字段 [英] Accessing protected fields of base class from derived (ES2019 private class)

问题描述

我想从派生类访问基类的私有字段，而不是将它们公开(在其他语言中称为受保护").

考虑以下类:

class Animal {#privateProp;构造函数(){this.#privateProp = 12;}}

现在是扩展类:

class Cat extends Animal {构造函数(){极好的();}做它(){console.log(this.#privateProp)//1 下面console.log(super.#privateProp)//2 下面}}

我想像受保护一样执行:

new Cat().doIt();

但是得到(分别):

<块引用>

1. 未捕获的语法错误:必须在封闭类中声明私有字段#privateProp"
2. 未捕获的语法错误:意外的私有字段

请注意，当 privateProp 变为 public 时，此代码将完美运行，但我想实现类似受保护的行为，并像任何支持继承的语言一样访问私有"字段.

任何帮助将不胜感激.

解决方案

您可以使用 getter 和 setter 方法创建私有属性通过检查构造函数是否不属于父类本身.

class Animal {#privateProp = 12;设置 Prop(val) {if (this.constructor.name !== 'Animal')返回 this.#privateProp = val;throw new Error('无法访问受保护的属性');}获取道具(){if (this.constructor.name !== 'Animal')返回这个.#privateProp;throw new Error('无法访问受保护的属性');}}类猫扩展动物{获取道具(){返回 super.Prop;}设置 Prop(val) {super.Prop = val}}让 cat = new Cat();console.log(cat.Prop)cat.Prop = 22console.log(cat.Prop)console.log(new Animal().Prop);

I'd like to access private fields of base class from derived classes without making them public (what is called 'protected' in other languages).

Consider the following class:

class Animal {

  #privateProp;

  constructor() {

  this.#privateProp = 12;

  }
}

Now the extending class:

class Cat extends Animal {

  constructor() {

    super();
  }

  doIt() {

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

I'd like to execute as if it was protected:

new Cat().doIt();

But gets (respectively):

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

Notice that this code would work perfectly when privateProp becomes public, But I want to achieve a protected like behavior and get access to the 'private' fields like any language that support inheritance.

Any help will be appreciated.

解决方案

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);

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