udpEcho.js

const RECEIVE_PORT = 3001;
const SEND_PORT = 3002;

const dgram = require('dgram');
const server = dgram.createSocket('udp4');

server.on('listening', function () {
    let address = server.address();
    console.log(`UDP server listening on ${address.address}:${address.port}`);
});

server.on('message', function (message, remote) {
    console.log(remote.address + ':' + remote.port +' - ' + message);

    //echo the message on sending port and append 'echo: ' string before message
    const echoBuf = Buffer.from('echo: ');
    server.send([echoBuf, message], SEND_PORT, remote.address);
});

server.bind(RECEIVE_PORT);