While conencting mongoDb with application facing issue : "UnhandledPromiseRejectionWarning: MongooseServerSelectionError: connect ECONNREFUSED 127.0.0.1:27017"

Tried Solutions :

1. Reinstalling mongoDb
2. Restarting the mongoDb service from control panel services.
3. Reinstalling the mongoose.

Code :

var express = require('express');
var app = new express();
var bodyParser = require('body-parser')
var mongoose = require('mongoose')
var user = require('./model/user')
const hostname = '127.0.0.1';
const port = 3000;
var router = express.Router();
mongoose.connect('mongodb://localhost:27017/userdb', { useNewUrlParser: true });
var users = [{ name: "Jane", age: 20 }, { name: "Mark", age: 40 }, { name: "Janefer", age: 40 }]
app.use(bodyParser.urlencoded({ extended: true }))//converts it into obj

router.route('/users')
    .get((req, res) => {
        //fetch record from users collectiobn
        user.find({}, (err, users) => {
            if (err) {
                res.json({ msg: 'error in fetching data from DB' })
            }
            else {
                res.json(users)
            }
        })
        // res.json(users)
    })
    .post((req, res) => {

    })
app.use('/api', router)//middleware to direct all req 
app.listen(port, hostname, () => {
    console.log("Server listening on 3000")
})

Error screenshot :

enter image description here