如何指定 var 中间语句的类型

Question

I used to have this line in my code:

let initialPayload = this.db.list("/members").snapshotChanges() as Observable<any[]>

Which changed to this line:

let initialPayload = this.db.list("/members").snapshotChanges()
.pipe(map(actions => actions.map(a => ({ key: a.payload.doc.id, data: a.payload.doc.data() }) )));

However, in the second line, I am getting an error: Property 'doc' does not exist on type DatabaseSnapshot<unknown>

And I suspect that the solution to this error is to bring back the as Observable<any[]> from the initial code. But I don't know how to add it to the second line. Should it go like this (?):

let initialPayload = this.db.list("/members").snapshotChanges()
.pipe(map(actions => actions.map(a => ({ key: a.payload.doc.id, data: a.payload.doc.data() }) ))) as Observable<any[]>

-?

If so, then my suspicions were wrong (because the error still persists after adding it at the end). But I need to make sure I've added it properly, so I would appreciate a confirmation of this.

Also since you've read this far, you're welcome to answer this question too: Error: Property 'doc' does not exist on type 'DatabaseSnapshot<unknown>'

Answer 1

Solved it. It had nothing to do with the types. It was probably because I was relying on a code related to firebase firestore, while I was actually using firebase reraltime database in my project.

The error I was getting because of doc was sovled by simply removing it and using the correct variables, as such:

let initialPayload = this.db.list("/members").snapshotChanges()
.pipe(map(actions => actions.map(a => ({ key: a.payload.key, data: a.payload.val() }) ))) as Observable<any[]>

Answer 2

Sounds like the as keyword which is similar to a cast. a as T would treat a as type T .