const Net = require('net'),
  NetKeepAlive = require('net-keepalive')
// or
import * as Net from 'net'
import * as NetKeepAlive from 'net-keepalive'

// Create a TCP Server
const srv = Net.createServer((s) => {
  console.log('Connected %j', s.address())
  // Doesn't matter what it does
  s.pipe(s)
})

// Start on some port
srv.listen(1337, () => {
  console.log('Listening on %j', srv.address())
})

// Connect to that server
const s = Net.createConnection({ port: 1337 }, () => {
  console.log('Connected to %j', s.address())

  //IMPORTANT: KeepAlive must be enabled for this to work
  s.setKeepAlive(true, 1000)

  // Set TCP_KEEPINTVL for this specific socket
  NetKeepAlive.setKeepAliveInterval(s, 1000)

  // Get TCP_KEEPINTVL for this specific socket
  NetKeepAlive.getKeepAliveInterval(s) // 1000

  // Set TCP_KEEPCNT for this specific socket
  NetKeepAlive.setKeepAliveProbes(s, 1)

  // Get TCP_KEEPCNT for this specific socket
  NetKeepAlive.getKeepAliveProbes(s) // 1
})

const NetKeepAlive = require('net-keepalive')
// or
import * as NetKeepAlive from 'net-keepalive'

// .....

const enable = true                                             // enable SO_KEEPALIVE
const initialDuration = 1000                                    // start probing after 1 second of inactivity
socket.setKeepAlive(enable, initialDuration)                    // sets SO_KEEPALIVE and TCP_KEEPIDLE

const probeInterval = 1000                                      // after initialDuration send probes every 1 second
NetKeepAlive.setKeepAliveInterval(socket, probeInterval)        //sets TCP_KEEPINTVL

const maxProbesBeforeFail = 10                                  // after 10 failed probes connection will be dropped
NetKeepAlive.setKeepAliveProbes(socket, maxProbesBeforeFail)    // sets TCP_KEEPCNT

// ....