How To Blink Border When Validation Fails

<div style="margin:auto;width:80%"><br />
       User Name : <asp:TextBox ID="txtUser" runat="server" CssClass="normalBorder" /><br /><br />
       Password : <asp:TextBox ID="txtPass" runat="server" CssClass="normalBorder" /><br /><br />
       <asp:Button ID="btnValidate" runat="server" Text="Validate" />
   </div>

<style type="text/css">
        .normalBorder{
            border:2px solid black;
        }
        .ValidateBorder{
            border:2px solid red;
        }
    </style>

<script src="scripts/jquery-3.1.0.min.js"></script>
<script type="text/javascript">
       $(document).ready(function () {
            $("#btnValidate").click(function () {
                if ($("#txtUser").val() == "") {

                    var $txt = $("#txtUser");
                    setInterval(function(){
                        $txt.toggleClass("ValidateBorder");
                    }, 500);
                    return false;
                }
                else {
                    $("#txtUser").class("normalBorder");
                }
            });
            $("#txtUser").focus(function () {

                $("#txtUser").css("borderColor", "black");
            });
        });
    </script>