Чтение текста из элемента управления метками ASP (заполняется jquery)

<script src = "https://code.jquery.com/jquery-1.12.4.min.js"></script>
<script type = "text/javascript">
  $(document).ready(function() {
    $("button").click(function() {
      var items = [];
      $.each($("input[name]:checked"), function() {
        items.push($(this).val());
      });
      //alert("You entered: " + items.join(", "));
      if (items.length === 0) {
        $('#<%=Label1.ClientID%>').html("No data to display.");
      } else {
        items = items.join(", ");
        $('#<%=Label1.ClientID%>').html("You selected the following options: " + "<br />");
        $('#<%=txtTestVar1.ClientID%>').html(items);
      }
    });
  });
</script>

<button type = "button" runat = "server">Update Choices <i class = "fas fa-retweet"></i></button>
<br />
<br />
<asp:Label runat = "server" ID = "Label1"></asp:Label>
<asp:Label runat = "server" ID = "txtTestVar1"></asp:Label>

protected void btnSave_Click(object sender, EventArgs e) { lblNotification.Text = txtTestVar1.Text.ToString(); }