Firebase Cloud Functions - How to use same return value in multiple .then() methods

Question

I'm trying to write a Firebase Cloud Function that does the following, using the Firebase Admin SDK:

1. Creates user with email/password.
2. Creates a Firestore doc, with reference the newly created UID.
3. Returns a Firebase JWT token to the client, if 1 & 2 are successful.

The code I have so far is below:

exports.createUser = functions.https.onCall((data, context) => {
    return admin
      .auth()
      .createUser({
        email: data.email,
        password: data.password,
        phoneNumber: data.number,
      })
      .then((user) => {
        return admin
          .firestore()
          .collection("collectionName")
          .doc(user.uid)
          .set({});
      })
      .catch((error) => {
        console.log("Error creating new user:", error);
      });
  });

What I'm struggling with is the next .then() in the chain, to return the JWT token. I'm aware of the actual Admin SDK code to return a JWT, but I'm not sure how I can access the new user's properties in multiple .then() s, while also returning a promise (which I think is necessary for proper function termination?)

How can I add another .then() that has access to user.uid and also ensures the function instance is not prematurely terminated?

Answer 1

You can simply use a variable as shown below:

exports.createUser = functions.https.onCall((data, context) => {

    let userObject;

    return admin
      .auth()
      .createUser({
        email: data.email,
        password: data.password,
        phoneNumber: data.number,
      })
      .then((user) => {
        userObject = user
        return admin
          .firestore()
          .collection("collectionName")
          .doc(user.uid)
          .set({});
      })
      .then(() => {
        const user = userObject;
        // Do whathever you want with user
        await function(user)
        
        // Don't forget to return data that can be JSON encoded, see the doc: https://firebase.google.com/docs/functions/callable#sending_back_the_result
        // In your case the JWT Object I guess
        return ...
      })
      .catch((error) => {
        console.log("Error creating new user:", error);
        // See the doc: https://firebase.google.com/docs/functions/callable#handle_errors
      });
  });

---

If you use async/await it is even easier:

exports.createUser = functions.https.onCall(async (data, context) => {

    const user = await admin
      .auth()
      .createUser({
        email: data.email,
        password: data.password,
        phoneNumber: data.number,
      });

    await admin
          .firestore()
          .collection("collectionName")
          .doc(user.uid)
          .set({}); 

    // Do whathever you want with user
    await function(user)

    return ...

  });