firestore update array
let washingtonRef = db.collection('cities').doc('DC'); // Atomically add a new region to the "regions" array field. let arrUnion = washingtonRef.update({ regions: admin.firestore.FieldValue.arrayUnion('greater_virginia') }); // Atomically remove a region from the "regions" array field. let arrRm = washingtonRef.update({ regions: admin.firestore.FieldValue.arrayRemove('east_coast') });