javascript - JavaScript 中的平等问题

Question

我不明白为什么此代码片段中的最后一行返回 false。是不是和上面那行一样？

const Statuses = Object.freeze({
  UNKNOWN : 0,
  OK      : 1,
  ERROR   : 2,
  STOPPED : 3
});

class myStatus extends Object{
  constructor() {
    super();
    this.status_id = Statuses.UNKNOWN;
  }
  valueOf(){
    return this.status_id;
  }
  getStatus(){
    return this.status_id;
  }
}

var a = new myStatus();
a.status_id = Statuses.ERROR;
console.log(a == Statuses.ERROR);
console.log(a.getStatus() === Statuses.ERROR);
console.log(a.valueOf() === Statuses.ERROR); //Isn't this the same as the line bellow?
console.log(a === Statuses.ERROR); //Why is this false but the rest are true?

http://jsbin.com/ritumesegi/edit?js,console

我得到 a == Statuses.ERROR 为 true，但其余的不应该给出相同的结果吗？尤其是最后2个。不是

a === Statuses.ERROR

同上

a.valueOf() === Statuses.ERROR

Answer 1

只是因为它们不是同一类型，请检查以下内容:

console.log(typeof(Statuses.ERROR)); // "number"
console.log(typeof(a) ); // "object"

区别:
== 仅评估值。
=== 评估值和类型。

引用:
https://www.w3schools.com/jsref/jsref_operators.asp

http://jsbin.com/jaquzikonu/edit?js,console