The lastDayOfMonth() method returns the start of the last day of the specified month.
DayPilot.Date.lastDayOfMonth();Returns a DayPilot.Date object representing the start of the last day of the month.
The returned value is normalized to the beginning of the day (T00:00:00).
const last = new DayPilot.Date("2020-02-01").lastDayOfMonth(); // new DayPilot.Date("2020-02-29T00:00:00")