plz-port/index.js

port scan

const net = require('net');
const MAXPORT = 65536;
const MINPORT = 3000; // avoid wellknown port
const portPromise = (beginPort) => {
  var PORT = parseInt(beginPort) || parseInt(Math.random() * (MAXPORT - MINPORT) + MINPORT);
  return new Promise((resolve, reject) => {
    const nextPort = () => {
      const port = PORT++;
      if (port <= 1) {
        return reject(new Error('Under min port number'));
      }
      if (port > 65536) {
        return reject(new Error('Over max port number'));
      }
      const server = net.createServer();
      server.on('error', (err) => {
        nextPort();
      });
      server.listen(port, () => {
        server.once('close', () => {
          resolve(port);
        });
        server.close();
      });
    };

    nextPort();
  });
};

module.exports = portPromise;