Select Menu Option <create On The Fly>

I am still having trouble creating the Select Menu option. I got parts
of the correct syntax but it is still not creating the selected carrier
as an option in the parent page.

Help apprecitate,. I currently have it commented out just to show the
line to you better:

function onCarrierSelect() {
var frm = document.carrRequestForm.carrierList.selectedIndex ;
var selectCar =
document.carrRequestForm.carrierList.options[frm].text;
var varEl = "<%=varElementName%>";
if (window.opener && !window.opener.close)
var oOption = window.opener.document.createElement("OPTION");
//window.opener.form.[varEl].options.add(oOption);
oOption.innerText =selectCar;
oOption.value =selectCar;
window.close();
}