[jQuery] datepicker is not a function

[jQuery] datepicker is not a function


$('.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)
            };
}

startDate: <input type="text" id="startDatepicker" class =
"Datepicker1">


endDate: <input type="text" id="endDatepicker" class =
"Datepicker1">