Firebase child_added for new items only

Question

I am using Firebase and Node with Redux. I am loading all objects from a key as follows.

firebaseDb.child(\'invites\').on(\'child_added\', snapshot => {
}         


        

Answer 1

If your document keys are time based (unix epoch, ISO8601 or the firebase 'push' keys), this approach, similar to the second approach @balthazar proposed, worked well for us:

const maxDataPoints = 100; 
const ref = firebase.database().ref("someKey").orderByKey();
// load the initial data, up to whatever max rows we want
const initialData = await ref.limitToLast(maxDataPoints).once("value")
// get the last key of the data we retrieved
const lastDataPoint = initialDataTimebasedKeys.length > 0 ? initialDataTimebasedKeys[initialDataTimebasedKeys.length - 1].toString() : "0"
// start listening for additions past this point...
// this works because we're fetching ordered by key
// and the key is timebased
const subscriptionRef = ref.startAt(lastDataPoint + "0");
const listener = subscriptionRef.on("child_added", async (snapshot) => {
    // do something here
});