@sean ok will try it out later =)

btw Thanks for the great tutorial for developing module from @Sean !!
Head first developing MM module for extreme beginners

Thanks bro!:smiling_face_with_open_mouth_smiling_eyes: this work for me!! after did below code then success to run the code already.

cd ~/MagicMirror/modules/MMM-hellotsuhan
npm install --save-dev electron-rebuild
./node_modules/.bin/electron-rebuild

Now my node_helper.js is :

const firebase = require ('firebase')
var NodeHelper = require("node_helper")
let countdown;
var ref;
var config = {
    apiKey: "AIzaSyAxi_kFKM3lxMZ9gnBMhwoPa7pxKX_e1BI",
    authDomain: "customerservice-ee487.firebaseapp.com",
    databaseURL: "https://customerservice-ee487.firebaseio.com",
    projectId: "customerservice-ee487",
    storageBucket: "customerservice-ee487.appspot.com",
    messagingSenderId: "466622230094"
};
if (!firebase.apps.length) {
    firebase.initializeApp(config);
}
module.exports = NodeHelper.create({
    start: function() {
       ref = firebase.app().database().ref().child('countdown');
       r ef.once('value').then(function (snap) {
         console.log('snap.val()', snap.val());
         countdown=snap.val();
       });
  },
  socketNotificationReceived: function(notification, payload) { 
      switch(notification) {
         case "DO_YOUR_JOB":   
           ref.once('value').then(function (snap) {
              console.log('snap.val()', snap.val());
	      countdown=snap.val();
	  });
          this.sendSocketNotification("I_DID", countdown - payload);      
	  break
      }
  }, 	
})

My MMM-hellotsuhan.js

Module.register("MMM-hellotsuhan",{
    start: function (){
        this.count = 0
    },
    getDom: function() {
        var element = document.createElement("div")
	element.className = "myContent"
	element.innerHTML = "Hello, World! " + this.config.foo
        var subElement = document.createElement("p")
	subElement.id = "COUNT"
	element.appendChild(subElement)
	return element
    },
    notificationReceived: function(notification, payload, sender) { 
        switch(notification) {
	    case "DOM_OBJECTS_CREATED":
	        var timer = setInterval(()=>{
	            this.sendSocketNotification("DO_YOUR_JOB", this.count)
	            this.count++
	        }, 1000)
	        break
	    }
    },
    socketNotificationReceived: function(notification, payload) {
        switch(notification) {
	    case "I_DID":
	        var elem = document.getElementById("COUNT")
	        elem.innerHTML = "Count:" + payload
	        break
	   }
        },
});	

@sean said in include npm module like firebase module into our own MM module:

i tried node helper. below code is working. But once i added const firebase = require (‘firebase’) on top then error appeared.

var NodeHelper = require("node_helper")

module.exports = NodeHelper.create({
  start: function() {
    this.countDown = 10000000
  },
  socketNotificationReceived: function(notification, payload) {
    switch(notification) {
      case "DO_YOUR_JOB":
        this.sendSocketNotification("I_DID", (this.countDown - payload))
        break
    }
  },
})

The error is

WARNING! Could not load config file. Starting with default configuration. Error found: Error: Failed to load gRPC binary module because it was not installed for the current system
Expected directory: electron-v2.0-linux-arm-glibc
Found: [node-v59-linux-arm-glibc]
This problem can often be fixed by running "npm rebuild" on the current system
Original error: Cannot find module '/home/pi/MagicMirror/modules/MMM-hellotsuhan/node_modules/grpc/src/node/extension_binary/electron-v2.0-linux-arm-glibc/grpc_node.node'

I tried npm rebuild. but still not working

How to include npm module like firebase module into our own MM module?
i tried include module using const firebase = require(‘firebase’). But keep getting error