Question

class Counter {

  constructor(initialValue = 0) {
    this.value = initialValue;
  }

  increment() {
    this.value += 1;
  }

}

const counter = new Counter();

console.log(counter.value); // 0

counter.increment();
console.log(counter.value); // 1

counter.value = 42; // <-- any way to forbid this?

counter.increment();
console.log(counter.value); // 43 :(

Answer 1

我不知道有什么方法可以在实例上获得值，但只有在类实例函数体外部访问时才禁止写访问。如果您只想在类实例方法（get和set）中访问，可以查看私有字段：github.com/tc39/proposal-private-fields

您还可以使用getters和WeakMaps来处理这些限制：

counter.js：

const privateProps = new WeakMap();
const get = instance => privateProps.get(instance);
const set = (instance, data) => privateProps.set(instance, data);

export default class Counter {

  constructor(initialValue = 0) {
    set(this, { value: initialValue });
  }

  increment() {
    get(this).value += 1;
  }

  get value() {
    return get(this).value;
  }

}

main.js

import Counter from 'counter.js';

const counter = new Counter();

console.log(counter.value); // 0

counter.increment();
console.log(counter.value); // 1

counter.value = 42; // <-- don't define a getter to forbid this

counter.increment();
console.log(counter.value); // 2 :)

有没有办法只通过类方法使类字段可变？

1 个答案: