Get user timezone string with Javascript / PHP?

Question

I\'m trying to get the user\'s timezone as a string on singup. example:

$timezone = \"Asia/Tel_Aviv\";

While researching the issue, I got

Answer 1

You need to follow answers of Nicholas Pickering and deceze♦ partially. Do not use PHP's timezone_name_from_abbr function(Ref).

Follow these steps to get UTC time of any timezone set in user system:

1. Javascript (client-side):

   var dateVar = new Date();
   var offset = dateVar.getTimezoneOffset();
   //getTimezoneOffset - returns the timezone difference between UTC and Local Time
   document.cookie = "offset="+offset;
   

2. Php (server-side):

   public function convert_utc_time($date)
   {
       $time_difference = isset($_COOKIE['offset'])?$_COOKIE['offset']:'';
       if($time_difference != ''){
           $time = strtotime($date);
           $time = $time + ($time_difference*60); //minutes * 60 seconds
           $date = date("Y-m-d H:i:s", $time);
       } //on failure of js, default timezone is set as UTC below
       return $date;
   }
   ..
   ..
   //in my function
   $timezone = 'UTC';
   $date = $this->convert_utc_time($post_date); //$post_date('Y-m-d H:i:s')
   echo strtotime($date. ' '. $timezone)