ช่วยด้วยจ้าคือผมจะส่งค่าในฟังค์ชัน callback ยังไงดีใน Node JS

var MongoClient = require('mongodb').MongoClient;
var url = "mongodb://localhost:27017/";

module.exports = {
	connect_db: function(callback) { // ส่ง callback กลับไป
		MongoClient.connect(url, function(err, db) {	
			if (err) throw err;
			callback( db.db("dbtest") ); 
		});
	},
	select_cl: function(dbo){ // ผ่านค่าตัวแปรมาตรงๆ
		dbo.collection("admin").findOne({}, function(err, result) {
			console.log(result.title);
		});
	}
};
func.connect_db( (rs)=>{
	func.select_cl(rs);
	res.render('index.ejs');
});   // ใส่ callback เรียกอีกชั้น

// Library All
var express = require('express');
var app     = express();

app.set('view engine','ejs');
app.use(express.static(__dirname));

// Call Mongo DB
var mongo = require("./mongo.js");
mongo.connect();

app.get('/', function (req, res) {

 	mongo.getdb().collection("info").find({}).toArray(function(err, result) {
		if (err) throw err;
		console.log(result);
	});

	res.render('index.ejs');
	
});


var server = app.listen(1000, function () {
   var host = server.address().address;
   var port = server.address().port;
   console.log("Example app listening at http://%s:%s", host, port);
}); 

//Config DB
var MongoClient = require('mongodb').MongoClient;
var url = "mongodb://localhost:27017/";
var db_name = "test";

// System DB
var odb = "";
var database = "";
module.exports = {
	connect: function() { 
		MongoClient.connect(url,{ useNewUrlParser: true }, function(err, db) {	
			if (err) throw err;
			odb = db;
			database = db.db(db_name);
		});
	},
	disconnect: function() { 
		odb.close();
	},
	getdb: function() { 
		return database;
	}
};