echo-server.js

const express = require('express')
const os = require('os');
const app = express()

app.get('/', function (req, res) {
  res.send('Response from ' + getIPAddress())
})

function getIPAddress() {
  var interfaces = require('os').networkInterfaces();
  for (var devName in interfaces) {
    var iface = interfaces[devName];
    for (var i = 0; i < iface.length; i++) {
      var alias = iface[i];
      if (alias.family === 'IPv4' && alias.address !== '127.0.0.1' && !alias.internal)
        return alias.address;
    }
  }
  return '0.0.0.0';
}

app.listen(8080, function () {
  console.log('Echo server listening on port 8080!')
})