Session update for javasript request

<?php
class MY_Session extends CI_Session
{

    function sess_update ()
    {
        // Listen to HTTP_X_REQUESTED_WITH
        if (isset($_SERVER['HTTP_X_REQUESTED_WITH']) && $_SERVER['HTTP_X_REQUESTED_WITH'] !== 'XMLHttpRequest') {
            // This is NOT an ajax call
            parent::sess_update();
        }
    }
}