portInUse.js

const net = require('net');

module.exports = function(port, callback) {
    const server = net.createServer(function(socket) {
	socket.write('Echo server\r\n');
	socket.pipe(socket);
    })

    server.listen(port, '127.0.0.1');
    server.on('error', function (e) {
	callback(true)
    })
    server.on('listening', function (e) {
	server.close()
	callback(false)
    })
}