findOpenPort.js

const net = require('net');

const isPortOpen = async (port, { timeout = 1000, host } = {}) => {
  const promise = new Promise(((resolve, reject) => {
    const socket = new net.Socket();

    const onError = () => {
      socket.destroy();
      reject();
    };

    socket.setTimeout(timeout);
    socket.once('error', onError);
    socket.once('timeout', onError);

    socket.connect(port, host, () => {
      socket.end();
      resolve();
    });
  }));

  try {
    await promise;
    return false;
  } catch (_) {
    return true;
  }
};

const findOpenPort = async (port) => {
  const isOpen = await isPortOpen(port);
  if (isOpen) { return port; }
  return findPort(port + 1);
};

module.exports = findOpenPort;