how to connect mongodb and nodejs

1//with mongoose 
2
3const mongoose = require('mongoose');
4
5mongoose.connect(
6    mongoURI,
7    {
8        useNewUrlParser: true,
9        useUnifiedTopology: true
10    },
11    (err) => {
12        if (err) console.log(err);
13        app.listen(3000);
14    }
15);
16/********************************************************************/
17// with mongodb lib
18const mongodb = require('mongodb');
19
20const MongoClient = mongodb.MongoClient;
21
22let _db;
23// you can replace test with any database name that you want
24const mongoConnect = (cb) => {
25  MongoClient.connect('mongodb://127.0.0.1:27017/test')
26    .then((client) => {
27      _db = client.db();
28      cb()
29      console.log('Connected to MongoDb');
30    }).catch((err) => {
31      console.log(err);
32    });
33}
34//after your server started you can use getDb to access mongo Database
35const getDb = () => {
36  if (_db) return _db;
37  throw 'No database found';
38}
39
40exports.mongoConnect = mongoConnect;
41exports.getDb = getDb;

1async function main(){
2    /**
3     * Connection URI. Update <username>, <password>, and <your-cluster-url> to reflect your cluster.
4     * See https://docs.mongodb.com/ecosystem/drivers/node/ for more details
5     */
6    const uri = "mongodb+srv://<username>:<password>@<your-cluster-url>/test?retryWrites=true&w=majority";
7 
8
9    const client = new MongoClient(uri);
10 
11    try {
12        // Connect to the MongoDB cluster
13        await client.connect();
14 
15        // Make the appropriate DB calls
16        await  listDatabases(client);
17 
18    } catch (e) {
19        console.error(e);
20    } finally {
21        await client.close();
22    }
23}
24
25main().catch(console.error);
26

1const {MongoClient} = require('mongodb');
2