Custom Validator Example

JavaScript Code:

<script type="text/javascript">
    function Check(sender, e) {
        if (isNaN(e.Value))
            e.IsValid = false;
        else
            e.IsValid = true;
    }
</script>

ASPX Code :

<asp:TextBox ID="TextBox1" runat="server" Width="150"></asp:TextBox>
    <asp:CustomValidator ID="CustomValidator1" runat="server"
        ErrorMessage="Id Should be a Number" ClientValidationFunction="Check"
        ControlToValidate="TextBox1" Display="Dynamic" ForeColor="Red"
        SetFocusOnError="True"></asp:CustomValidator>