check if a port is being used with nodejs

isPortTaken.js

const net = require('net')

function isPortTaken(port) {
  return new Promise((resolve, reject) => {
    const tester = net.createServer()
    tester.once('error', err => {
      if (err.code != 'EADDRINUSE')
        return reject(err)
      resolve(true)
    })
    .once('listening', () => tester.once('close', () => resolve(false)).close())
    .listen(port)
  })
}