Can Cloud Firestore onSnapshot() only trigger on changes, and not get the initial state?

Question

The documentation says:

You can listen to a document with the onSnapshot() method. An initial call using the callback you provide creates a document s

Answer 1

Firestore listeners don't work that way. You will always be delivered the document(s) relevant to the fetch or query, then updates after that for as long as the listener remains added. There is no mode to receive deltas only.

If you want to receive only certain data, you might want to figure out how to query for it, for example, by adding a timestamp field and having the client only query for documents that have changed since some prior time.