index.html

<!doctype html>
<html>

<head>
  <title>SaveBot</title>
</head>

<body>
  <ul id="messages"></ul>
  <form action="">
    <input id="m" autocomplete="off" />
    <button>Send</button>
  </form>

  <script src="/socket.io/socket.io.js"></script>
  <script src="https://code.jquery.com/jquery-1.11.1.js"></script>
  <script>
    let context = null;
    $(function () {
        var socket = io();
        $('form').submit(function () {
          socket.emit('chat message', {
            context: context,
            msg: $('#m').val(),
          });
          $('#messages').append($('<li>').text($('#m').val()));
          $('#m').val('');
          return false;
        });

        socket.on('chat message', function (response) {
          context = response.context;
          $('#messages').append($('<li>').text(response.msg));
        });
      });
  </script>
</body>

</html>