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')
});
Egg Salad