MongooseServerSelectionError: connect ECONNREFUSED 127.0.0.1:27017

I used mongoose to connect my database to my app.

I got this unexpected error.

My app.js look like this

const express = require('express');
const mongoose = require('mongoose');
const authRoutes = require('./routes/authRoutes');
const cookieParser = require('cookie-parser');
const { requireAuth, checkUser } = require('./middleware/authMiddleware');
const run = require('./admin/connection');

const app = express();

// middleware
app.use(express.static('public'));
app.use(express.json());
app.use(cookieParser());

const {default : AdminBro} = require('admin-bro');
const buildAdminRouter = require('./admin/admin.router');
const options = require('./admin/admin.options');
const port = 3000;


const url = 'mongodb://localhost:27017/dbName';
let mongooseDb;
const databaseConnect = async () => {
  mongooseDb = await mongoose.connect(url, { useNewUrlParser: true, useUnifiedTopology: true, useCreateIndex:true })
  .then((result) => app.listen(3000))
  .catch((err) => console.log(err));

  const db = mongoose.connection;
  db.on('error', console.error.bind(console, 'connection error:'));
  db.once('open', function() {
    console.log("we are connected to database");
  });
  
    const admin = new AdminBro(options)
    const router = buildAdminRouter(admin);
    app.use(admin.options.rootPath, router);

  
};
databaseConnect();

I already installed mongodb database.

I already find similar question in stackoverflow but that answers didn't resolve my issue. Any help will be appreciated. Thanks