Script to dynamically adapt timezones

supertime.js

var times = document.getElementsByClassName("supertime");

for (var i = 0; i < times.length; i++) {
  var timezone = times[i].dataset.timezone;
  var timeoffset = calculatetimeoffset(timezone.substring(4));

  var flag = "add";

  var giventime = times[i].innerHTML;

  if (timezone.charAt(3) == "+") {
    flag = "subtract";
  }

  giventime = absolutetime(giventime);

  var utctime;
  if (flag == "add") {
    utctime = giventime + timeoffset;
  } else {
    utctime = giventime - timeoffset;
  }

  var utcoffset = new Date().getTimezoneOffset();

  var adjustedtime = utctime - utcoffset;

  times[i].innerHTML = formatTime(adjustedtime);
}

function calculatetimeoffset(timestring) {
  var time_division = timestring.split(":");
  var offset;
  if (time_division.length > 1) {
    offset = parseInt(time_division[0]) * 60 + parseInt(time_division[1]);
  } else {
    offset = parseInt(time_division[0]) * 60;
  }

  return offset;
}

function absolutetime(timestring_2) {
  var time_division_1 = timestring_2.split(":");
  var absolute;
  if (time_division_1.length > 1) {
    absolute = parseInt(time_division_1[0]) * 60 + parseInt(time_division_1[1]);
  } else {
    absolute = parseInt(time_division[0]) * 60;
  }

  return absolute;
}

function formatTime(settime) {
  var hours = Math.floor(settime / 60);
  var minutes = settime % 60;

  newtime = hours + ":" + minutes;

  return newtime;
}