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Accordding to my last question SerialPort 'close' event never fire . I was unabled to detected if the COM is disconnected so I have created my own way to detect it.

I have created timestamp, and checked it with interval() every 1 sec to see if it is connected. when it's detect the COM is unplugged I have try to re-establish the connection or re-instance port with SerialPort like you'll see inside the code below.

When it's try to reconnect I've get Error: Access denied.

There is a way to refresh or clean the cache? , because I think the server still hold the connection when isn't closed propely.

I've also tried port.close() and it's throw me out: Error: Port is not open.

var comPort = '\\\\.\\COM7',
    lastDataTime,
    lastresult,
    count = 0,
    lastDataTime,
    comStatus,
    error;
var port = new SerialPort(comPort, function (err) {
    if (err) {
        comStatus = false;
        return console.log('Error: ', err.message);
const parser = port.pipe(new Readline());
port.on('open', function () {
    console.log('~Port is open.');
    parser.on('data', function (data) {
        comStatus = true;
        lastDataTime = Date.now();
        if (++count == 10) {
            count = 0;
            lastresult = data;
setInterval(function () {
    if (Date.now() - lastDataTime > 1000 || !comStatus) {
        comStatus = false;
        port.close();
        port = new SerialPort(comPort, function (err) {
            if (err) {
                error = 'Error: ' + err.message;
                return console.log(error);
}, 1000);
app.get('/', function (req, res) {
    res.send((comStatus) ? lastresult : 'Disconnected - ' + error);
    console.log(lastresult);
Thanks!
As you can see in /node_modules/serialport/lib/serialport.js: close-event may not be emitted (unlike disconnect). 
You can add console.log locally like below to simple debug.
P.S. I tested it on Win7x32. Close-event is emitted.
SerialPort.prototype._disconnected = function(err) {
  this.paused = true;
  this.emit('disconnect', err);
  // add: console.log('1', this.closing);
  if (this.closing) {
    return;
  // add: console.log('2', this.fd);
  if (this.fd === null) {
    return;
  this.closing = true;
  if (process.platform !== 'win32') {
    this.readable = false;
    this.serialPoller.close();
  // add: console.log('3');
  SerialPortBinding.close(this.fd, function(err) {
    // add: console.log('4', this._events.close.toString());
    this.closing = false;
    if (err) {
      debug('Disconnect close completed with error: ', err);
    this.fd = null;
    this.emit('close'); // it's your target
  }.bind(this));
var SerialPort = require('serialport');
var port = new SerialPort('COM1', {autoOpen: false, baudRate: 9600});
function open () {
    port.open(functon (err) {
        if (!err)
           return;
        console.log('Port is not open: ' + err.message);
        setTimeout(open, 10000); // next attempt to open after 10s
port.on('open', function() {
    function send() {
        if (!port.isOpen()) // v5.x require
            return console.log('Port closed. Data is not sent.');
        port.write(123, function (err) {
            if (err)
                console.log('Error on write: ' +  err.message)
            port.drain(() => console.log('DONE'));
    setInterval(send, 1000);
port.on('close', function () {
    console.log('CLOSE');
    open(); // reopen 
port.on('data', (data) => console.log('Data: ' + data));
port.on('error', (err) => console.error('Error: ', err.message));
open(); // open manually
                Thanks that helped!, after the event fire i've tried reconnect the COM but after i reconnect it the data stop flowing. do you know how to reconnect after disconnect?
– Itzik.B
                Sep 19, 2017 at 22:41
  
The resume() method causes an explicitly paused, Readable stream to
  resume emitting 'data' events, switching the stream into flowing mode.
Simply, when port is closes, serialport library emits a close event
serialport.on('close', function(error){
  if(error.disconnected === true){
    console.log("disconnected");
, which will allow us whether port is disconnected or not. 
That means the disconnected port is not available to re-establish the connection again, so you have to use serialport.resume() method to re-enable the connection.
serialport.on('close', function(err){
  console.log("Port closed.");
  if(err.disconnected === true){
    console.log("Disconnected!");
    serialport.resume(function(e){
      reconnectDevice(); // Serial Port Initialization Function. It's your method to declare serial port.
      console.log("Error on resuming port:", e);
After that, it will automatically switch COM ports and you won't get error as 'Port Access denied.'.
        
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