CRM 2011 Javascript - Lokup Alanın Id sini Alma (Get Lookup Id)

function GetLookupId(fieldName) {
    var lookupObject = Xrm.Page.getAttribute(fieldName).getValue();
    if (lookupObject != null && lookupObject != undefined) {
        if (lookupObject[0].id != "")
            return lookupObject[0].id;
    }

    return "00000000-0000-0000-0000-000000000000";
}