NodeJS is port taken

is_port_taken.js

function isPortTaken(port, fn) {
  var net = require('net')
  var tester = net.createServer()
    .once('error', function(err) {

      return fn(err);

    })
    .once('listening', function() {
      
      tester.once('close', function() {

          fn(false);

      }).close()

    })
    .listen(port)
};

/* Usage */

isPortTaken(80, (err) => {
  
  if(!err) createMyServer();
  
});