Get difference between two timezones

timezone.js

console.log(getTZDiff('UTC+5:30','UTC+8:00'));

function getTZDiff(currentTz, otherTz) {
  var selectedTz = new Date('January 1, 1970 00:00:00 ' + currentTz);
  var targetTz = new Date('January 1, 1970 00:00:00 ' + otherTz);
  var difference = selectedTz.getTime() - targetTz.getTime(); 
  var hours = (difference / 3600000);
  if (hours < 0) return Math.abs(hours) + " hours behind";
  return Math.abs(hours) + " hours ahead";
}