Assigning document ID from collections

We use Vue together with Firestore and have problems with a function that creates a document in a collection. We want to create a collection of lobbies where each lobby has its own chat. For that we need to create a collection with messages in that lobby which we just created. The problem is that our function createLobby() returns the variable ID before it has been assigned the correct ID. This can be seen in the console log picture.