How local connect mongodb

npm i mongodb

database.js

const mongodb = require('mongodb');
const MongoClient = mongodb.MongoClient;

let database;

// connect to local mongodb
async function connectToDatabase() {
  const client = await MongoClient.connect("mongodb://localhost:27017");
  database = client.db('db_name');
}

// get database
function getDb() {
	if(!database) {
      throw new Error('Connect to mongodb first')
    }
  return database;
}

async function(connectToDatabase) always returns Promise

app.js

const db = require('/data/database');

// listen port if connected sucessfully
db.connectToDatabase()
  .then(() => app.listen(3000))
  .catch((err) =>
    console.log(`Failed to connect to the databse with this error: ${err}`)
  );