How to get data from Firestore in map function

Question

I want to retrieve data from Firestore as I map through an object to see if the user is online. I'm not sure how to retrieve the data.

When I console.log userInLobby (as shown below), I get [Promise] array.

If I try to set a variable before the firebase call, I cannot change the variable inside the .then() function

 const userInLobby = users ? (
  users.map(userdata => {
    if (userdata.status === "online") {
      var user =
        firebase.firestore().collection("users").doc(userdata.id).get().then(user => {
          return { username: user.data().username };
        })
      return user
    }
    else {
      return null;
    }
  })
) : (null);

How can I access the [Promise] or is there another way to structure this code?

Josh Pittman · Accepted Answer · 2019-02-09 19:33:09Z

2

It looks like you are trying to run an asyncronous function (firebase.firestore().collection("users").doc(userdata.id).get()) inside a map function.

That won't work. The map function will just return an array of promises.

What you need to do is use Promise.all() to get the result when all the promises return.

const userInLobby = users
  && users.map(userdata => {
      if (userdata.status === 'online') {
        return firebase
          .firestore()
          .collection('users')
          .doc(userdata.id)
          .get()
      } 
    })

Promise.all(userInLobby).then(values => console.log(values))

answered Feb 9, 2019 at 19:33

Josh Pittman

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