Chat Samle not work!

[Vasya]

        connection.start()
            .then(function (connection) {
                console.log(connection);

connection started, ok. but after that
here connection is undefined and of course all other not work

[Matt Collins]

Replace the script on line 25 in your index.html with the below script: Hopefully it fixes it for you.

<script type="text/javascript">
    document.addEventListener('DOMContentLoaded', function () {

        var messageInput = document.getElementById('message');

        // Get the user name and store it to prepend to messages.
        var name = prompt('Enter your name:', '');
        // Set initial focus to message input box.
        messageInput.focus();

        // Start the connection.
        startConnection('/chat', function (connection) {

            // Create a function that the hub can call to broadcast messages.
            connection.on('broadcastMessage', function (name, message) {
                // Html encode display name and message.
                var encodedName = name;
                var encodedMsg = message;
                // Add the message to the page.
                var liElement = document.createElement('li');
                liElement.innerHTML = '<strong>' + encodedName + '</strong>:&nbsp;&nbsp;' + encodedMsg;
                document.getElementById('discussion').appendChild(liElement);
            });
        })
            .then(function (connection) {
                console.log('connection started');
                document.getElementById('sendmessage').addEventListener('click', function (event) {
                    // Call the Send method on the hub.
                    connection.invoke('send', name, messageInput.value);

                    // Clear text box and reset focus for next comment.
                    messageInput.value = '';
                    messageInput.focus();
                    event.preventDefault();
                });
            })
            .catch(error => {
                console.error(error.message);
            });
        // Starts a connection with transport fallback - if the connection cannot be started using
        // the webSockets transport the function will fallback to the serverSentEvents transport and
        // if this does not work it will try longPolling. If the connection cannot be started using
        // any of the available transports the function will return a rejected Promise.
        function startConnection(url, configureConnection) {
            return function start(transport) {
                console.log(`Starting connection using ${signalR.TransportType[transport]} transport`)
                var connection = new signalR.HubConnection(url, { transport: transport });
                if (configureConnection && typeof configureConnection === 'function') {
                    configureConnection(connection);
                }

                return connection.start()
                    .then(function () {
                        return connection;
                    })
                    .catch(function (error) {
                        console.log(`Cannot start the connection use ${signalR.TransportType[transport]} transport. ${error.message}`);
                        if (transport !== signalR.TransportType.LongPolling) {
                            return start(transport + 1);
                        }

                        return Promise.reject(error);
                    });
            }(signalR.TransportType.WebSockets);
        }
    });
</script>

[David Fowler]

Fixed it