Install MongoDB into API

npm i mongodb

Import MongoClient

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

Create MongoDB Client By Passing DB Server URL

// Database URL
const dbURL = 'mongodb://127.0.0.1:27017';

// Create MongoDB Client
const mc = new MongoClient(dbURL);

Connecting to mongodb

// Connect to MongoDB
mc.connect().then(client => {
    console.log('Connected to MongoDB');
}).catch(err => {
    console.log('Error in connecting to MongoDB');
});

Connecting to database & collection

// Connect to MongoDB
mc.connect().then(connectionObject => {
    
    // Connect to Database
    const usersDatabase = connectionObject.db('First');
    
    // Connect to Collection
    const usersCollection = usersDatabase.collection('Users');
    
    // Share the Collection with the APIs
    app.set('usersCollection', usersCollection);
    
    console.log('Connected to MongoDB');
    
    // Assign Port Number to Server
    const port = 4000;
    app.listen(port, () => {
        console.log(`Server running on port <http://localhost>:${port}`);
    });
}).catch(err => {
    console.log('Error in connecting to MongoDB');
});

In API Get Collection object , Write the mongoDB command and send the response to Client

// GET Request
userApp.get('/users', async (req, res) => {
    
    // Get usersCollection object
    const usersCollection = req.app.get('usersCollection');

    // Get Users data from usersCollection of DB
    let users = await usersCollection.find().toArray();

    // Send the data to the client
    res.send(users);

});