Get an available port from a promise using the nodejs net module

get-available-port.js

const net = require('net')

async function getAvailablePort () {
  return new Promise((resolve, reject) => {
    let server = net.createServer()
    server.unref()
    server.on('error', reject)

    // zero gives it away ;)
    server.listen(0, () => {
      let port = server.address().port

      server.close(() => {
        resolve(port)
      })
    })
  })
}