Javascript 如何检入具有angular2键的对象

我有以下对象let usersVal=snapshot.val（）

console.log

3TngNGbwMVhc5kJ2b3wAULEIP6g1
    Object
    photoUrl
    "https://scontent.xx.fbcdn.net/v/t1.0-1/ss"
    provider
    "facebook.com"
    signup
    1480596548396
    useremail
    "someemail@yahoo.com"
    username
    "James nan"
    __proto__


 c834vePyJ3SFVk2iO4rU0ke1cSa2
    photoUrl
    "https://firebasestorage.googleapis.com/v0/b/ff"
    provider
    "google.com"
    signup
    1480600290735
    useremail
    "3333@gmail.com"
    username
    "Ericel123eessdd"
    __proto__
    Object

我想检查对象是否有uid密钥。如果是，我将一些boolan值设置为true

this.users = af.database.object('/some-users', { preserveSnapshot: true });
    this.users.subscribe(snapshot => {
      let usersVal = snapshot.val();
      if(key in usersVal){
        this.userId = true;
      }

});

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如何在angular2组件中实现这一点？

应尽可能简单

let usersVal = snapshot.val();
if (usersVal["uid"]) {
    ...
}

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你提供的代码有什么问题？