var numberOfLinesBeforeScroll = 10;

var linesPrintCounter = 0;

function log(msg) {

    var node = document.createElement("tr"); // we create new row

    var textnode = document.createTextNode(linesPrintCounter + "|" + msg);

    node.appendChild(textnode); // adding text to "node"

    divElement.insertBefore(node, divElement.childNodes[0]);

    if (linesPrintCounter > numberOfLinesBeforeScroll-1) {

        divElement.removeChild(divElement.childNodes[numberOfLinesBeforeScroll]);

    }

    linesPrintCounter++; // increase the counter of printouts

}

- fs.readFile(__dirname + "/example08.html",

+ fs.readFile(__dirname + "/example09.html",

wss.broadcast("Remote IP addres -> ws._socket.remoteAddress: " + ws._socket.remoteAddress);

// ::ffff:192.168.254.1 is ipv6 address

// in Chrome we enter: http://[::ffff:192.168.254.131]:8080 -> http://[::ffff:c0a8:fe83]:8080

wss.broadcast("Websocket data -> ws._socket.address(): " + JSON.stringify(ws._socket.address()));

wss.broadcast("Websocket data address -> ws._socket.address().address: " +

JSON.stringify(ws._socket.address().address));

wss.broadcast("Websocket data family -> ws._socket.address().family: " +

JSON.stringify(ws._socket.address().family));

wss.broadcast("Websocket data port -> ws._socket.address().port: " +

JSON.stringify(ws._socket.address().port));

wss.broadcast("Remote port -> ws._socket.remotePort: " + ws._socket.remotePort);

wss.broadcast("Client data ----------------------------->");    

wss.broadcast = function broadcast(data) {

  wss.clients.forEach(function each(client) {

      if (client.readyState === WebSocket.OPEN) {

    client.send(data);

      }

  });

};

var http = require("http").createServer(handler);

var fs = require("fs"); // variable for file system

var firmata = require("firmata");

const WebSocket = require('ws');

const wss = new WebSocket.Server({port: 8888}); // web socket server wss

wss.broadcast = function broadcast(data) {

  wss.clients.forEach(function each(client) {

      if (client.readyState === WebSocket.OPEN) {

    client.send(data);

      }

  });

};

var board = new firmata.Board("/dev/ttyACM0", function(){ // ACM Abstract Control Model for serial communication with Arduino (could be USB)

    console.log("Connecting to Arduino");

    console.log("Activation of Pin 13");

    board.pinMode(13, board.MODES.OUTPUT); // Configures the specified pin to behave either as an input or an output.

    console.log("Enabling pin 2 for button");

    board.pinMode(2, board.MODES.INPUT);

});

function handler(req, res) {

    fs.readFile(__dirname + "/example09.html",

    function (err, data) {

        if (err) {

            res.writeHead(500, {"Content-Type": "text/plain"});

            return res.end("Error loading html page.");

        }

    res.writeHead(200);

    res.end(data);

    });

}

http.listen(8080); // server will listen on port 8080 to serve html page

var sendValueViaWebSocket = function(){};

board.on("ready", function() {

wss.on('connection', function (ws) {

    ws.send("Server connected, board OK.");

    console.log('ws._socket.remoteAddress', ws._socket.remoteAddress);

    console.log('ws._socket.address', ws._socket.address());

    console.log('ws._socket.remotePort', ws._socket.remotePort);

    // print of IP adresses, ports, ip family

    wss.broadcast("Remote IP addres -> ws._socket.remoteAddress: " + ws._socket.remoteAddress);

    // ::ffff:192.168.254.1 is ipv6 address

    // in Chrome we enter: http://[::ffff:192.168.254.131]:8080 -> http://[::ffff:c0a8:fe83]:8080

    wss.broadcast("Websocket data -> ws._socket.address(): " + JSON.stringify(ws._socket.address()));

    wss.broadcast("Websocket data address -> ws._socket.address().address: " + JSON.stringify(ws._socket.address().address));

    wss.broadcast("Websocket data family -> ws._socket.address().family: " + JSON.stringify(ws._socket.address().family));

    wss.broadcast("Websocket data port -> ws._socket.address().port: " + JSON.stringify(ws._socket.address().port));

    wss.broadcast("Remote port -> ws._socket.remotePort: " + ws._socket.remotePort);

    wss.broadcast("Client data ----------------------------->");    

    sendValueViaWebSocket = function(value) {

        ws.send(value);

    }

}); // end of wss code

    var timeout = false;

    var last_sent = null;

    var last_value = null;

    board.digitalRead(2, function(value) { // this happens many times on digital input change of state 0->1 or 1->0

        if (timeout !== false) { // if timeout below has been started (on unstable input 0 1 0 1) clear it

         clearTimeout(timeout); // clears timeout until digital input is not stable i.e. timeout = false

        }

        timeout = setTimeout(function() { // this part of code will be run after 50 ms; if in-between input changes above code clears it

            console.log("Timeout set to false");

            timeout = false;

            if (last_value != last_sent) { // to send only on value change

             if (value == 0) {

                    console.log("LED OFF");

                    board.digitalWrite(13, board.LOW);

                    console.log("value = 0, LED OFF");

                }

                else if (value == 1) {

                    console.log("LED ON");

                    board.digitalWrite(13, board.HIGH);

                    console.log("value = 1, LED lit");

                }

                sendValueViaWebSocket("Value = " + value.toString()); // ws transfers only string

            }

            last_sent = last_value;

        }, 50); // execute after 50ms

        last_value = value; // this is read from pin 2 many times per s

    }); // end board.digitalRead on pin 2

});  // end of board.on "ready"

<!DOCTYPE html>

<meta charset = utf8>

<html>

<head>

    <title>Example with HW button</title>

</head>    

<body>

<div id="print1"></div>

<script type="text/javascript">

"use strict"; // in order to use clasess

var numberOfLinesBeforeScroll = 30;

var linesPrintCounter = 0;

var divElement = document.getElementById("print1"); // var for div el.

function log(msg) {

    var node = document.createElement("tr"); // we create new row

    var textnode = document.createTextNode(linesPrintCounter + "|" + msg);

    node.appendChild(textnode); // adding text to "node"

    divElement.insertBefore(node, divElement.childNodes[0]);

    if (linesPrintCounter > numberOfLinesBeforeScroll-1) {

        divElement.removeChild(divElement.childNodes[numberOfLinesBeforeScroll]);

    }

    linesPrintCounter++; // increase the counter of printouts

}

var ws = new WebSocket('ws://192.168.254.149:8888/');

ws.onmessage = function (event) {

    log(event.data);

}

ws.onclose = function (value) {

    log("Connection closed.");

}

</script>

</body>    

</html>