échec de la connexion de localhost:8081 en utilisant node.js

Question

J'ai ouvert le server.js et l'adresse : http://localhost:8081 sur mon navigateur. Mais un texte "Upgrade Required" est apparu dans le coin supérieur gauche du site. Quel est le problème de ce texte ? De quoi ai-je besoin pour effectuer la mise à niveau ?

Voici le server.js :

var serialport = require('serialport');
var WebSocketServer = require('ws').Server;

var SERVER_PORT = 8081;
var wss = new WebSocketServer({
    port: SERVER_PORT
});
var connections = new Array;

SerialPort = serialport.SerialPort,
portName = process.argv[2],
serialOptions = {
    baudRate: 9600, 
    parser: serialport.parsers.readline('\n')
};
if (typeof portName === "undefined") {
    console.log("You need to specify the serial port when you launch this script, like so:\n");
    console.log("    node wsServer.js <portname>");
    console.log("\n Fill in the name of your serial port in place of <portname> \n");
    process.exit(1);
}

var myPort = new SerialPort(portName, serialOptions);

myPort.on('open', showPortOpen);
myPort.on('data', sendSerialData);
myPort.on('close', showPortClose);
myPort.on('error', showError);

function showPortOpen() {
    console.log('port open. Data rate: ' + myPort.options.baudRate);
}

function sendSerialData(data) {
    if (connections.length > 0) {
        broadcast(data);
    }
}

function showPortClose() {
    console.log('port closed.');
}

function showError(error) {
    console.log('Serial port error: ' + error);
}

function sendToSerial(data) {
    console.log("sending to serial: " + data);
    myPort.write(data);
}

wss.on('connection', handleConnection);

function handleConnection(client) {
    console.log("New Connection");
    connections.push(client);

    client.on('message', sendToSerial);
    client.on('close', function () {
        console.log("connection closed");
        var position = connections.indexOf(client);
        connections.splice(position, 1);
    });
}
function broadcast(data) {
    for (c in connections) {
        connections[c].send(data);
    }
}