Datepicker field should be readonly using jquery

I have this code  

          $("#FromDate").datepicker({
                changeMonth: true,
                changeYear: true,
                yearRange: "-100:+10",
                dateFormat: 'dd-M-yy',
                onSelect: function (dateStr) {
                    var max= new Date(dateStr);
                    max.setDate(max.getDate() + 1);
                    $('#ToDate').datepicker('setDate', max);
                    $("#ToDate").attr('readonly', true);
                }

            });

ToDate datepicker date is set properly and also looked readonly. but when i click on ToDate it's shows me the date calendar. which should not populated as per my need.
Kindly suggest what should I do?

$("#ToDate").attr('readonly', true);