ShowHide_Div_on Checkbox click in javascript

Head section

<script language="javascript" type="text/javascript">
    
     function ShowHideFranchise()
     {       
         if (document.getElementById('<%=chkcouncelling.ClientID %>').checked == true)
         {          
             document.getElementById('<%=pnlcouncel.ClientID %>').style.visibility = "visible";
         }
         else
         {
             document.getElementById('<%=pnlcouncel.ClientID %>').style.visibility = "hidden";
         }
     }
    
 </script>

Body Section

<asp:CheckBox ID="chkcouncelling" runat="server" />

<div id="pnlcouncel" runat="server" style="visibility: hidden; width: 100%">

</div>



inside Page_load  (!ispostback)

chkcouncelling.Attributes.Add("onclick", "javascript:ShowHideFranchise('" + chkcouncelling.ClientID + "')");