从对象检索值

Question

我正在尝试从对象中获取价值。

当我执行与此调查相关的用户console.log(poll.user)时

首先得到未定义，然后

{_id: "5bd99816068dee45fddf317e", username: "Karolina"}

我对_id

感兴趣

所以我尝试使poll.user._id变得不确定。...

但是如果我在poll.user上使用for in，则它具有值

PS投票将作为道具

致谢

投票价值

date: "2018-10-31T11:55:27.343Z"
options: (2) [{…}, {…}]
question: "Java or Python?"
user: {_id: "5bd99816068dee45fddf317e", username: "Karolina"}
voted: (2) ["5bd99816068dee45fddf317e", "5bd2ef4f755aa221a9cc6f6d"]
__v: 2
_id: "5bd9982f068dee45fddf317f"
__proto__: Object

实际上，这给了我价值

let uu;
if (poll.user) {
  uu = poll.user._id;
}
console.log(uu);

Answer 1

尝试

let userId = null;
if(poll && poll !== undefined && poll.user !== undefined && poll.user._id && poll.user._id !== undefined)
  userId = poll.user._id;
console.log(userId )

Answer 2

您可以使用下面的&&运算符同时获取用户ID和用户名

   const userId = poll && poll.user && poll.user._id;
   const userName = poll && poll.user && poll.user.username;