Transform a Firebase.Firestore.QuerySnapshot into an iteratable

firestoreIterator.js

function fetchAll() {
  return firebase.firestore().collection('objects').get().then(snapshot => (
    {
      [Symbol.iterator]: function iterator() {
        const { docs } = snapshot;

        return {
          next() {
            return {
              done: docs.length === 0,
              value: docs.length && docs.shift().data()
            };
          }
        };
      },
      raw: snapshot,
      forEach: snapshot.forEach,
      map: fn => docs.map(doc => fn(doc.data()))
    }
  ))
}

fetchAll().then(response => {
  // transform it into an array
  const array = Array.from(response);

  // spread in an array
  const state = [/* lots of objects here */];
  const newState = [...state, ...response];
  
  // in a for..of loop
  for(doc of response) {
    console.log(doc);
  }
  
  // map function
  response.map(doc => console.log(doc))
});