Firebase child_added for new items only

Although the limit method is pretty good and efficient, but you still need to add a check to the child_added for the last item that will be grabbed. Also I don't know if it's still the case, but you might get "old" events from previously deleted items, so you might need to watch at for this too.

Other solutions would be to either:

Use a boolean that will prevent old added objects to call the callback

let newItems = false

firebaseDb.child('invites').on('child_added', snapshot => {
  if (!newItems) { return }
  // do
})

firebaseDb.child('invites').once('value', () => {
  newItems = true
})

The disadvantage of this method is that it would imply getting events that will do nothing but still if you have a big initial list might be problematic.

Or if you have a timestamp on your invites, do something like

firebaseDb.child('invites')
  .orderByChild('timestamp')
  .startAt(Date.now())
  .on('child_added', snapshot => {
  // do
})

I have solved the problem using the following method.

firebaseDb.child('invites').limitToLast(1).on('child_added', cb)
firebaseDb.child('invites').on('child_changed', cb)

limitToLast(1) gets the last child object of invites, and then listens for any new ones, passing a snapshot object to the cb callback.

child_changed listens for any child update to invites, passing a snapshot to the cb