How to split EventDate and EndDate

i am trying to split on "," working with eventdate and endate but i dont get it to work. (undenified)

    var listEventDate = oListItem.get_item('EventDate');
    var listEventdt = new Date(listEventDate);
    var listEndDate = oListItem.get_item('EndDate');
    var listEventEnddt = new Date(listEndDate);



            var string= listEventdt + "," + listEventEnddt;
            var res = string.split(",");

            for (var j = 0; j < res.length; j++) {

                var item = new Date(listEventdt)[j];
                var item2 = new Date(listEventEnddt)[j];

                    } 

Any Suggestions?