Firestore batch update

update_batch.js

function updateCollection(db, collectionRef, newData, batchSize) {
  // console.log('updateCollection') 
  var query = collectionRef.orderBy('__name__').limit(batchSize);

  return new Promise(function(resolve, reject) {
    updateQueryBatch(db, query, batchSize, newData, resolve, reject);
  });
}

function updateQueryBatch(db, query, batchSize, newData, resolve, reject) {
  // console.log('updateQueryBatch')
  query.get()
  .then((snapshot) => {
    // console.log('updateQueryBatch: snapshot.size = ', snapshot.size)
    // When there are no documents left, we are done
    if (snapshot.size == 0) {
      return 0;
    }

    // Delete documents in a batch
    var batch = db.batch();
    snapshot.docs.forEach(function(doc) {
      batch.update(doc.ref, newData);
    });

    return batch.commit().then(function() {
      return snapshot.size;
    });
  }).then(function(numUpdated) {
    if (numUpdated <= batchSize) {
      resolve();
      return;
    }

    // Recurse on the next process tick, to avoid
    // exploding the stack.
    process.nextTick(function() {
      updateQueryBatch(db, query, batchSize, newData, resolve, reject);
    });
  })
  .catch(reject);
}