Using OrderdMap from immutable.js with firebase javascript example.

firebase-immutable-js-orderedmap.js

const { OrderedMap } = require('immutable');
var documentMap = OrderedMap()

const messageListner = () => {
    let unsubscribe = database
        .collection('documents')
        .orderBy('created_at', 'asc')
        .limitToLast(10)
        .onSnapshot(async (snap) => {
            for (let msg of snap.docs) {
                documentMap = documentMap.set(msg.data().created_at, msg.data())
            }
        }, (err) => {
            unsubscribe();
        })

}