How to change the date format in ServiceNow ?

var startTime  = new GlideDateTime(current.variables.reactivation_end_date);
 var dateToPrint = startTime.getDate();
var startTime1  = new GlideDateTime(dateToPrint.getByFormat('YYYY-dd-MM'));
  var endTime = new GlideDateTime();
   var dur = GlideDateTime.subtract( startTime1, endTime); 
 gs.info("dur.getDayPart()"+dur.getDayPart());
 gs.info("dur.getDayPart()startTime"+startTime);
 gs.info("dur.getDayPart()endTime"+endTime);