CODE EXAMPLE FOR JAVASCRIPT

angularjs How to get time difference from ZoneDateTime in javascript

function getTimeDiff(data, date = new Date()) {
  let utc = new Date(Date.UTC(
      data.year, 
      data.monthValue - 1,
      data.dayOfMonth,
      data.hour,
      data.minute,
      data.second
  ) - data.offset.totalSeconds*1e3);
  return date - utc;
}

function msToTime(ms) {
  let days = ms / 8.64e7 | 0;
  let hrs = (ms%8.64e7) / 3.6e6 | 0;
  let mins = (ms%3.6e6) / 6e4 | 0;
  let secs = (ms%6e4) / 1e3 | 0;
  let z = n => (n<10? '0':'') + n;
  return `${days? days + ' day' + (days == 1? ' ' : 's ') : ''}${z(hrs)}:` +
         `${z(mins)}:${z(secs)}`;
}

let callStartTime = {
  chronology: {id: 'ISO', calendarType: 'iso8601'},
  dayOfMonth: 8,
  dayOfWeek: "TUESDAY",
  dayOfYear: 39,
  hour: 16,
  minute: 15,
  month: "FEBRUARY",
  monthValue: 2,
  nano: 240000000,
  offset: {totalSeconds: 19800, id: '+05:30', rules: {}},
  second: 29,