How to detect user's timezone?

Question

I need to know what time zone is currently my users are in based on their IP or http header.

I got many answer regarding this issue, but i could not understood thos

Answer 1

Timezone is not available in the HTTP header, but country (abbreviation) is in the ACCEPT_LANGUAGE header. It'll be something like "en-US" (US is the country code). This can be combined with the JavaScript information to get a good idea of the user's timezone.

This is what I'm using in JS:

function timezone() {
  var now = new Date();
  var jano = new Date(now.getFullYear(), 0, 1).getTimezoneOffset()/-60;
  var julo = new Date(now.getFullYear(), 6, 1).getTimezoneOffset()/-60;
  var tz = Math.min(jano, julo);
  if (jano != julo) tz += ((jano < julo) ? 'S' : 'W') + Math.abs(jano - julo);
  return tz;
}

This returns a string like "-6S1" for the central zone (standard time offset of -6 hours, DST active in the summer and adds 1 hour). I use a cookie to make this available to PHP. PHP searches the TZ database for zones that match this, and the country. For here (US, -6S1) there are 7 matching zones, the first is "America/Chicago".

BTW, there are 2 zones in the database where DST adds something other than 1 hour: Lord Howe Island (10.5W0.5) and Troll Station, Antarctica (0W2).