Datetimepicker Date different

I want to date difference between using datetimepicker not datepicker .how cant i get and i try but it's show " NaN " . below my javascript

        $('#myModal').on('show.bs.modal', function (event) {
            var button = $(event.relatedTarget)
            var fromDate = button.data('fromdate')
            var toDate = button.data('todate')

            var from = $('#fromDate').val();

                var to = $('#toDate').val();
                var diff = Date(to - from);
                var days = diff/1000/60/60/24;
                
            console.log(days)
    )};