get a new/clean port with node.js

gistfile1.js

var portrange = 45032

function getPort (cb) {
  var port = portrange
  portrange += 1

  var server = net.createServer()
  server.listen(port, function (err) {
    server.once('close', function () {
      cb(port)
    })
    server.close()
  })
  server.on('error', function (err) {
    getPort(cb)
  })
}

see you and raise you @felipenmoura:

import { createServer } from 'net'
function getPort(port = 3000) {
  return new Promise((resolve, reject) => {
    const server = createServer()
    server.on('error', (err) => {
      if (err.code !== 'EADDRINUSE') return reject(err)
      server.listen(++port)
    })
    server.on('listening', () => server.close(() => resolve(port)))
    server.listen(port)
  })
}

usage: const port = await getPort()

see you and raise you @leviwheatcroft :)

import { createServer } from 'net'
function getPort() {
  return new Promise((resolve, reject) => {
    const server = net.createServer()
    server.on('error', reject)
    server.on('listening', () => (port => server.close(() => resolve(port)))(server.address().port))
    server.listen(0)
  })
}

I like this game, @ronen: ^_^

import { createServer } from 'net'
function getPort (port = 80) {
  const server = createServer()
  return new Promise((resolve, reject) => server
  .on('error', error => error.code === 'EADDRINUSE' ? server.listen(++port) : reject(error))
  .on('listening', () => server.close(() => resolve(port)))
  .listen(port))
}

Usage

const port = await getPort()

@ronen & @jonathantneal, reraise:

import { createServer } from 'net'

function getPort (port = 80, maxPort = 65535) {
  if ((maxPort = parseInt(maxPort)) < (port = parseInt(port))) {
    return Promise.reject((() => {
      const e = new Error('EPORTSPEC')
      e.code = e.message
      return e
    })())
  }
  const server = createServer()
  return new Promise((resolve, reject) => server
    .once('error', error => error.code !== 'EADDRINUSE' || ++port > maxPort ? reject(error) : server.listen(port))
    .once('listening', () => server.close(() => resolve(port)))
    .listen(port)
  )
}

NB: edited to remove port range checks since server.listen has that check; only need to check that maxPort > port.