Utility method to update more than 500 docs in Firestore using Batch. TypeScript.

firestore.utils.ts

import admin from 'firebase-admin';

/**
 * Firestore does not accept more than 500 writes in a transaction or batch write.
 */
const MAX_TRANSACTION_WRITES = 499;

type WriteBigBatchOperationType = (batch: admin.firestore.WriteBatch) => void;
type WriteBigBatchCallbackType = (operation: WriteBigBatchOperationType) => void;

/* Usage:
  await writeBigBatch(
    admin.firestore(), // firestore instance
    (resolveActiveBatch) => {
      // const docRef = ...
      // const data = ...
      resolveActiveBatch((writeBatch) => {
        writeBatch.set(docRef, data, {merge: true});
      });
      //...
    }
  );
*/
// Based on solution: https://stackoverflow.com/a/56145214/5925490
export const writeBigBatch = async (
    db: admin.firestore.Firestore,
    callback: (_:WriteBigBatchCallbackType) => void
) => {
  const batchPool: admin.firestore.WriteBatch[] = [];
  batchPool.push(db.batch());

  let operationCounter = 0;
  let batchIndex = 0;

  callback((operation: WriteBigBatchOperationType) => {
    operation(batchPool[batchIndex]);

    operationCounter++;
    if (operationCounter === MAX_TRANSACTION_WRITES) {
      batchPool.push(db.batch());
      batchIndex++;
      operationCounter = 0;
    }
  });

  batchPool.forEach(async (batch) => {
    await batch.commit();
  });
};