function getTimezoneOffset() {
  function z(n){return (n<10? '0' : '') + n}
  var offset = new Date().getTimezoneOffset();
  var sign = offset < 0? '+' : '-';
  offset = Math.abs(offset);
  return sign + z(offset/60 | 0) + z(offset%60);
}

getTimezoneOffset() // +0800 for UTC/GMT + 8hrs