detect client timezone

localTimezone.js

//********* Timezone calculation
  var localTimezone = function(){
    var timezone = ""
    var d = new Date;
    var offset = d.getTimezoneOffset()
    timezone = (offset > 0) ? "-" : "+"
    offset = offset / 60 * (-100)
    var paddedOffset = pad(""+offset,4,'0');
    return timezone + paddedOffset
  }

var strRepeat = function(str, qty){
  if (qty < 1) return '';
  var result = '';
  while (qty > 0) {
    if (qty & 1) result += str;
    qty >>= 1, str += str;
  }
  return result;
};

var pad = function(str, length, padStr, type) {
  str = str == null ? '' : String(str);
  length = ~~length;

  var padlen  = 0;

  if (!padStr)
    padStr = ' ';
  else if (padStr.length > 1)
    padStr = padStr.charAt(0);

  switch(type) {
    case 'right':
      padlen = length - str.length;
      return str + strRepeat(padStr, padlen);
    case 'both':
      padlen = length - str.length;
      return strRepeat(padStr, Math.ceil(padlen/2)) + str
              + strRepeat(padStr, Math.floor(padlen/2));
    default: // 'left'
      padlen = length - str.length;
      return strRepeat(padStr, padlen) + str;
    }
}