udp-echo.js

#!/usr/local/bin/node
let dgram = require('dgram')

let socket = dgram.createSocket('udp4', (msg, rinfo) => {
  let peer = `${rinfo.address}:${rinfo.port}`

  socket.send(msg, peer, (err) => {
    if (err) peer.close()
    console.log(`Sent ${rinfo.size} of ${rinfo.size} bytes to ${peer}`)
  })
})

socket.bind(8080, () => {
  let address = socket.address()
  console.log(`Listening on ${address.address}:${address.port}`)
})

We're trying to show a realistic depiction of how people would likely write a UDP server in Node. This is how I'd go about it if I was tasked with building a UDP server for a contract.