custom validation with javascript in asp.net c#

<script type="text/javascript">
    function ChkPcode(source,arguments)
    {
        var tb=document.getElementById('txtplancode');
        var rvalue=PlanMaster.GetPCode(arguments.Value);
        if(rvalue.value=="")
        {    arguments.IsValid=true; }
        else
        {    tb.value=""; arguments.IsValid=false; document.getElementById('planCdCV').innerHTML="Plan Code Already Exists"; }
    }
    </script>




 <asp:CustomValidator ID="planCdCV" runat="server" ErrorMessage="" SetFocusOnError="true"
                            ControlToValidate="txtplancode" Display="Dynamic" ClientValidationFunction="ChkPcode" ValidateEmptyText="True"></asp:CustomValidator>