I think this is how the code should look like
On button click prompt confirm
<asp:LinkButton ID="lnk_Delete" runat="server"
OnClientClick="return Confirm();">
<img src="../images/Document_Delete.png" alt="" />Delete</asp:LinkButton>
If yes, set hidden value and call return OpenSwipWindowAction (...) (Assuming it return true | false)
else (Cancel), return false, do nothing ( I'm assuming )
<script>
function Confirm() {
var confirm_value = document.createElement("INPUT");
confirm_value.type = "hidden";
confirm_value.name = "confirm_value";
if (confirm("Do you want to Delete data?")) {
confirm_value.value = "Yes";
document.forms[0].appendChild(confirm_value);
return OpenSwipWindowAction('Delete', '');
} else {
confirm_value.value = "No";
return false;
}
document.forms[0].appendChild(confirm_value);
}
</script>