Hello, I would use jQuery in fields and datefield textfield but I can not.
below is the code used.

<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="WebForm1.aspx.cs" Inherits="Sysmo.Web.WebForm1" %>
<%@ Register Assembly="Ext.Net" Namespace="Ext.Net" TagPrefix="ext" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head id="Head1" runat="server">
<title>Ext.Net Example</title>
<script src="Resources/js/jquery.min.js" type="text/javascript"></script>
<script src="Resources/js/jquery.maskedinput-1.3.js" type="text/javascript"></script>
<script>
jQuery(function ($) {
$("#txtTelephone").mask("(999) 999-9999");
});
</script>
</head>
<body>
<ext:ResourceManager ID="ResourceManager1" runat="server" />
<ext:TextField runat="server" ID="txtTelephone" FieldLabel="Telephone"></ext:TextField>
</body>
</html>