Firebase 9 array from onSnapshot

January 20, 2022

So I need to convert data from Firebase 9 snapshot to an array.

I’ve came up with something like this, but it doesn’t return anything.

Check comments in my code.

I suppose, I should use promises, but can’t figure out the right way.

const fetchNewMessages = async (threadId: string, latestTimestamp: any) => {
  const q = query(threadRef(threadId), orderBy('timestamp', 'asc'), startAfter(latestTimestamp));
  const messages: IMessage[] = [];
  onSnapshot(q, (querySnapshot) => {
    const docs = querySnapshot.docChanges();
    docs.forEach((change) => {
      if (change.type === "added")
        messages.push(fetchDoc(change.doc));
    });
    console.log(messages.length); // here I get 34
  });
  console.log(messages.length); // here I get 0
  return messages.reverse();
};

>Solution :

try to wait for "onSnapshot"

  const fetchNewMessages = (threadId: string, latestTimestamp: any) => {
  const q = query(threadRef(threadId), orderBy('timestamp', 'asc'), startAfter(latestTimestamp));
  const messages: IMessage[] = [];
  return new Promise((resolve) => {
    onSnapshot(q, (querySnapshot) => {
      const docs = querySnapshot.docChanges();
      docs.forEach((change) => {
        if (change.type === "added")
          messages.push(fetchDoc(change.doc));
      });
      resolve(messages.reverse());
    });
  });
};