Firestore transaction update multiple documents in a single transaction

I figured it out we can use multiple ref inside a transaction:

var userSuhail = db.collection("users").doc("suhail");
var userSam = db.collection("users").doc("sam");
var userJohn = db.collection("users").doc("john");
var userAlfred = db.collection("users").doc("Alfred");
var userAlfredDetails = db.collection('userdetails').doc('Alfred');

db.runTransaction(function (transaction) {
  return transaction.get(userJohn).then(function (sDoc) {
    var age = sDoc.data().age + 1;
    transaction.set(userAlfred, {
      name: 'Alfred',
      age,
      details: userAlfredDetails,
    });
    transaction.set(userAlfredDetails, {
      address: 'Alfred Villa',
    });
    transaction.update( userJohn   , { age, }, );
    transaction.update( userSuhail , { age, }, );
    transaction.update( userSam    , { age, }, );
    return age;
  });
}).then(function (age) {
  console.log("Age changed to ", age);
}).catch(function (err) {

  console.error(err);
});

By the above code the transaction updates age of all users.

You can use batch method which firebase provides. This is how I used it to store array of objects, creating multiple documents inside a newly created collection.

export const addCollectionAndDocuments = async (collectionKey, objectToAdd) => {
  console.log(collectionKey, objectToAdd);

  let collectionRef = firestore.collection(collectionKey);
  const batch = firestore.batch();
  objectToAdd.forEach(obj => {
    const newDocRef = collectionRef.doc();
    batch.set(newDocRef, obj);
  });
  return await batch.commit();
};