[jQuery] datepicker is not a function

[divsystem]

$('.Datepicker1').datepicker({beforeShow: customRange,
   rangeSelect: true, numberOfMonths: 2});

function customRange(input) {
    return {
                        minDate: (input.id == "startDatepicker" ? $
("#endDatepicker").datepick("getDate") : null),
                        maxDate: (input.id == "endDatepicker" ? $
("#startDatepicker").datepick("getDate") : null)
                        };
}



<p>startDate: <input type="text" id="startDatepicker" class =
"Datepicker1"></p>
<p>endDate: <input type="text" id="endDatepicker" class =
"Datepicker1"></p>