[PHP, Javascript] Detecting User Time Zone of a user

var now = new Date();
var later = new Date();
// Set time for how long the cookie should be saved
later.setTime(now.getTime() + 365 * 24 * 60 * 60 * 1000);
// Set cookie for the time zone offset in minutes
setCookie("time_zone_offset", now.getTimezoneOffset(), later, "/");
// Create two new dates
var d1 = new Date();
var d2 = new Date();
// Date one is set to January 1st of this year
// Guaranteed not to be in DST for northern hemisphere,
// and guaranteed to be in DST for southern hemisphere
// (If DST exists on client PC)
d1.setDate(1);
d1.setMonth(1);
// Date two is set to July 1st of this year
// Guaranteed to be in DST for northern hemisphere,
// and guaranteed not to be in DST for southern hemisphere
// (If DST exists on client PC)
d2.setDate(1);
d2.setMonth(7);
// If time zone offsets match, no DST exists for this time zone
if(parseInt(d1.getTimezoneOffset())==parseInt(d2.getTimezoneOffset()))
{
setCookie("time_zone_dst", "0″, later, "/");
}
// DST exists for this time zone – check if it is currently active
else {
// Find out if we are on northern or southern hemisphere
// Hemisphere is positive for northern, and negative for southern
var hemisphere = parseInt(d1.getTimezoneOffset())-parseInt(d2.getTimezoneOffset());
// Current date is still before or after DST, not containing DST
if((hemisphere>0 && parseInt(d1.getTimezoneOffset())==parseInt(now.getTimezoneOffset())) ||
(hemisphere<0 && parseInt(d2.getTimezoneOffset())==parseInt(now.getTimezoneOffset()))) { setCookie("time_zone_dst", "0″, later, "/"); } // DST is active right now with the current date else { setCookie("time_zone_dst", "1″, later, "/"); } }