ip.js

const ips = require('os').networkInterfaces()

const result = []

Object.keys(ips).forEach(function (ifname) {
  ips[ifname].forEach(function (iface) {
    if ('IPv4' !== iface.family || iface.internal !== false) {
      // skip over internal (i.e. 127.0.0.1) and non-ipv4 addresses
      return;
    }
    result.push(iface.address)
  });
});

module.exports = result[0] ? result[0] : '0.0.0.0'