MongoError: connection 0 to localhost:8081 closed at Function.MongoError.create

[mdmasumbillah]

Hello bro, When I run "nodemon server.js" then show this error. I'm tried for the error

# 1. server.js
var express = require('express');
var app = express();
var bodyParser = require('body-parser');
var morgan = require('morgan');
var passport = require('passport');
var ejs = require('ejs');
var session = require('express-session');
var flash = require('connect-flash');
var cookieParser = require('cookie-parser');
const mongoose = require('mongoose');
var dbUrl = require('./config/db.js').url;

var option = {
socketTimeoutMS: 30000,
keepAlive: true,
reconnectTries: 30000
};
// Connect to mongoose
mongoose.connect(dbUrl);
var db = mongoose.connection;
db.on('error', console.error.bind(console, 'connection error:'));
db.once('open', function () {
console.log('Connected');
});

app.use(flash());
app.use(session({
secret: 'meanlocalauth'
}));
app.use(bodyParser.json);
app.use(bodyParser.urlencoded({
extended: false
}))
app.use(passport.initialize());
app.use(passport.session());

require('./router/routes.js')(app);
// require('./passport.js')(app, passport);

app.use(morgan('dev'));
var PORT = process.env.PORT || 8081;
app.listen(PORT, function(){
console.log('Listening on port '+ PORT);
});

#2. db.js
module.exports = {
'url': 'mongodb://localhost:8081/loginapp'
}

# 3.package.json
{
"dependencies": {
"bcrypt-nodejs": "0.0.3",
"body-parser": "^1.18.3",
"connect-flash": "^0.1.1",
"cookie-parser": "^1.4.3",
"ejs": "^2.6.1",
"express": "^4.16.3",
"express-session": "^1.15.6",
"mongodb": "^3.0.10",
"mongoose": "^4.10.8",
"morgan": "^1.9.0",
"passport": "^0.4.0",
"passport-local": "^1.0.0"
},
"scripts": {
"start": "node server.js"
},
"name": "loginapp",
"version": "1.0.0",
"main": "server.js",
"devDependencies": {},
"author": "Masum",
"license": "MIT",
"description": ""
}

connection error: { MongoError: connection 0 to localhost:8081 closed
at Function.MongoError.create (/Users/ms/loginApp/node_modules/mongoose/node_modules/mongodb-core/lib/error.js:29:11)
at Socket. (/Users/ms/loginApp/node_modules/mongoose/node_modules/mongodb-core/lib/connection/connection.js:202:22)
at Object.onceWrapper (events.js:315:30)
at emitOne (events.js:116:13)
at Socket.emit (events.js:211:7)
at TCP._handle.close [as _onclose] (net.js:554:12)
name: 'MongoError',
message: 'connection 0 to localhost:8081 closed' }

[kishanjasani]

In the server.js

// Do have to require like this
var dbUrl = require('./config/db').url;

Not with .js extension

var dbUrl = require('./config/db.js').url;