es 6 类定义静态方法 静态常量 私有成员

静态方法

class Foo {
  static classMethod() {
    return 'hello';
  }
}

静态常量

class Foo  {
  constructor() {
    super();
  }
  static get StaticData(){
    return "default"
  }
}

只定义get方法不定义 set，有static set 则可修改了

私有成员

let _counter = new WeakMap();
let _action = new WeakMap();

class Countdown {
  constructor(counter, action) {
    _counter.set(this, counter);
    _action.set(this, action);
  }
  dec() {
    let counter = _counter.get(this);
    if (counter < 1) return;
    counter--;
    _counter.set(this, counter);
    if (counter === 0) {
      _action.get(this)();
    }
  }
}

let c = new Countdown(2, () => console.log('DONE'));

c.dec()
c.dec()
// DONE

使用WeakMap

const _counter = Symbol('counter');
  const _action = Symbol('action');
  
  class Countdown {
      constructor(counter, action) {
          this[_counter] = counter;
          this[_action] = action;
      }
      dec() {
          if (this[_counter] < 1) return;
          this[_counter]--;
          if (this[_counter] === 0) {
              this[_action]();
          }
      }
  }
// properties whose keys are symbols:

http://www.2ality.com/2016/01/private-data-classes.html