Question

I have to display a client side confirmation after calculating a complex formula server side. Something like

//Server side
        On ButtonClick(){
            FetchRate(field1,field2,.... fieldn);
            // Show Client side confirmation
            // Execute server side code if confirmed client side 
    }

What I have done is created a client side function but my server side code always executes on postback no matter what I select client side

// Server side    
ScriptManager.RegisterStartupScript(this,this.GetType(), Guid.NewGuid().ToString(), "ConfirmAction('"+ myRate +"');", true);
//Client side
    function ConfirmAction(myRate) {
            if (confirm('Are you sure?. Rate is exceeding '+ myRate +', proceed ?')) {
                document.getElementById('hfSaveUpdate').value = 1;
                return true;
            }
            else
                return false;
        }

Answer 1

You can use Ajax Model Popup & handle its ok & cancel button.

<ajaxToolkit:ModalPopupExtender ID="ModelPopupID" runat="server"  
    TargetControlID="LinkButton1"  
    PopupControlID="Panel1"  
    BackgroundCssClass="modalBackground"   
    DropShadow="true"   
    OkControlID="OkButton"   
    OnOkScript="onOk()"  
    CancelControlID="CancelButton"   
    PopupDragHandleControlID="Panel3" />  

Launching a Modal Popup Window from Server Code:

Server Side Code:

ClientScript.RegisterStartupScript(this.GetType(), "key", "launchModal();", true);

Client-Side Code:

<script type="text/javascript">
 var launch = false;
 function launchModal() 
 {
 launch = true;
 }
function pageLoad() 
 {
 if (launch) 
 {
 $find("ModelPopupID").show();
 }
 }
</script>

On ok click of the model popup, execute you server-side after conformation code.
On cancel button click, just hide the model popup window.

For more details, check this:

ModalPopup Tutorial