<%*
function pad(n) {
  return n.toString().padStart(2, "0");
}
function fmtDate(d) {
  var yyyy = d.getFullYear();
  var mm = pad(d.getMonth() + 1);
  var dd = pad(d.getDate());
  var dArr = [ yyyy, mm, dd ];
  return(dArr.join('-'));
}
function lastDay(a) {
  if (typeof(a) === 'undefined' || a === '') {
    var d = new Date();
  } else {
    var d = new Date(a + ' 12:00:00');
    if (d.toString() === 'Invalid Date') {
      console.log('invalid date');
      return
    }
  }
  var lastDay = new Date(d.getFullYear(),d.getMonth()+1,0);
  lastDate = fmtDate(lastDay)
  lastDay = lastDay.getDate()
  return lastDate // change to "lastDay" to output day only
} %><% lastDay(tp.file.selection())%>