Loopback Remote Method and Firebase Admin NodeJS

Question

I am currently trying to create a remote method in loopback that will query a firebase database using the Firebase Admin SDK in NodeJS.

It works, but the issue I am having is that I am unable to make it realtime. It keeps crashing with an error pointing to the callback function being called more than once.

Here is a snippet of the code for my remote method:

'use strict';

module.exports = function(Scusers) {
    var admin = require("firebase-admin");

    Scusers.listItems = function(cb) {        
        // Get a database reference        
        var db = admin.database();
        var ref = db.ref("users");    

        // Attach an asynchronous callback to read the data at our posts reference
        var items = [];

        // return list of users ordered by key and push each object into an array        
        ref.orderByKey().on("value", function(snapshot) {
            snapshot.forEach(function(data) {
                items.push(data.val());
            });

            // return array
            cb(null, items);
        }, function (errorObject) {
            console.log("The read failed: " + errorObject.code);
        });
    };
}

If I change this line:

ref.orderByKey().on

for:

ref.orderByKey().once

It works, but on my front-end which is coded in AngularJS, it won't see the changes unless I manually call a refresh.

What should be the best approach to this? Sorry if it is unclear or my approach is wrong, I am so new at this. Thanks!