Firestore transaction update multiple documents in a single transaction

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();
};

Proof of concept:

var transaction = firestore.runTransaction( t => {
  return t.get(eRef)
    .then(snapshot => {
      snapshot.forEach(doc => {
        var employee = doc.data();
        if(employee.status !== 'Off work') {
          t.update(doc.ref, {
            status: 'Off work',
            returnTime: '8 am'
          })
        }
      })
    })
}).then(result => {
  console.log('Transaction success!')
}).catch(err => {
  console.log('Transaction failure: ', err)
});

you can use this =>

firestore.collection("YOUR_COLLECTION_PATH")
    .get()
    .then(function(querySnapshot) {
        querySnapshot.forEach(function(doc) {
            console.log(doc.id, " => ", doc.data());
        });
    })
    .catch(function(error) {
        console.log("Error getting documents: ", error);
    });

Also if you want to map the querySnapshot in an array, you can do like this:

firestore.collection("YOUR_COLLECTION_PATH")
.get()
.then(function(querySnapshot) {
    var arrayDocs = querySnapshot.docs.map(docData=>docData.data())
    console.log(arrayDocs);
})
.catch(function(error) {
    console.log("Error getting documents: ", error);
});

The info is at https://firebase.google.com/docs/firestore/query-data/get-data