Below is a quote form https://bitbucket.org/pellepim/jstimezonedetect/wiki/Home:
To simply store away a user's timezone in a variable, you can simply import timezone_detect.js and do the following.
var timezone = determine_timezone().timezone; // Now you have an instance of the TimeZone object. alert(timezone.utc_offset); // Offset in minutes from UTC alert(timezone.olson_tz); // Olson database timezone key (ex: Europe/Amsterdam) alert(timezone.uses_dst); // bool for whether the tz uses daylight saving time
This gives you an Olson database key you can use for datetime calculations in most programming languages.
When the data is stored in a cookie, the php script can start to take over. we can call the cookie by simply calling the $_COOKIE["timezone_js"] and putting it in date_default_timezone_set($_COOKIE["timezone_js"] ). That way, your web is now in the same timezone as the client.
That's all from me, happy blogging!