Regular Expression for Alphanumeric using Javascript. You can use Javascripts to validate this as followes.
Define the Function "isNumberEvt" on Head Section. and check it on keypress even of text box like "onkeypress="return isNumberEvt(event)"".
Code :
<head runat="server">
<title>Untitled Page</title>
<script language="javascript" type="text/javascript">
function isNumberEvt(evt)
{
var charCode = (evt.which) ? evt.which : event.keyCode
if ((charCode > 31 && charCode < 48 ) || (charCode > 57 && charCode < 65 ) || (charCode > 90 && charCode < 97) || (charCode > 122))
return false;
return true;
}
</script>
</head>
<body>
<form id="form1" runat="server">
<div>
<asp:TextBox ID="TextBox1" runat="server" Width="238px" onkeypress="return isNumberEvt(event)"></asp:TextBox></div>
</form>
</body>