Cloud function - fan out post write

fanOutPostWrite.ts

export const fanOutPostWrite = functions.firestore
    .document('users/{uid}/posts/{postId}')
    .onWrite(async (change, context) => {
        const postId = context.params.postId;
        const uploader = context.params.uid;

        const followerRefs = await firestore
            .collection('users').doc(uploader)
            .collection('followers').get();

        let batchArray: FirebaseFirestore.WriteBatch[] = [];
        batchArray.push(firestore.batch());
        let operationCounter = 0;
        let batchIndex = 0;

        followerRefs.docs.forEach((doc) => {
            const followerId = doc.id;

            const followingFeedRef = firestore.collection('users').doc(followerId)
                .collection('feed').doc(postId);


            //On Delete
            if (!change.after.exists && change.before.exists) {

                batchArray[batchIndex].delete(followingFeedRef);

            } else {
                const data = change.after.data();
                batchArray[batchIndex].set(followingFeedRef, data);
            }

            operationCounter++;

            if (operationCounter === 499) {
                batchArray.push(firestore.batch());
                batchIndex++;
                operationCounter = 0;
            }
        });

        batchArray.forEach(batch => batch.commit());

        if (change.after.exists) {
            const myFeedRef = firestore.collection('users').doc(uploader)
                .collection('feed').doc(postId);

            console.log('should update this post on my feed', myFeedRef.path);
            return myFeedRef.set(change.after.data());
        }

        return null;
    });