not all code paths return value with multiple batch writes google firestore cloud function typescript

The problem isn’t with the batch. The problem is that your larger Cloud Functions code doesn’t return a promise that resolves when all the async work is complete (see the documentation on that). In fact, for the main if (newUsername !== oldUsername) block, your code returns nothing at all, and that’s a problem.

Minimally, you code should go more like this:

    if (newUsername !== oldUsername) {
      // ...
      const promiseA = conversationQueryA.get()
        // ...
      const promiseB = conversationQueryB.get()
        // ...
      return Promise.all([promiseA, promiseB])
    }
    else {
      return null
    }

Now it will return a value no matter which primary code path is taken, and it will return a promise that resolves only after both chains of async work are complete.