ModalPopupExtender postback dual Listbox

Question

I have dual listboxs (followed by http://www.meadmiracle.com/dlb/DLBDocumentation.aspx) which work well. Now I need a ModalPopupExtender page to confirm user's selected. when user click button submit the ModalPopupExtender will show.

<button id="btnSubmit" title="Submit" onclick="confirm(); return false;"> Submit </button>
<script language="javascript" type="text/javascript">
        function confirm() {
            $find('mpeOutConfirm').show();
            };
</script>

So far, everything is fine. But if I assign value to that confirmation page, like

function confirm() {
  $find('mpeOutConfirm').show();
   document.getElementsByID('cphContent_lblOutType').innerHTML = "test";
};

it will cause postback and Popup page will be gone and all selected items in listbox2 will disappeared.

Answer 1

my bad. should be getElementsById, not getElementsByID; fixed