function set_cookie(cookie_name, cookie_value, lifespan_in_days, valid_domain)
 {
    var domain_string = valid_domain ?
    ("; domain=" + valid_domain) : '';
    document.cookie = cookie_name +
    "=" + encodeURIComponent(cookie_value) +
    "; max-age=" + 60 * 60 *
    24 * lifespan_in_days +
    "; path=/" + domain_string;
}

function delete_cookie(cookie_name, valid_domain)
 {
    var domain_string = valid_domain ?
    ("; domain=" + valid_domain) : '';
    document.cookie = cookie_name +
    "=; max-age=0; path=/" + domain_string;
}

function get_cookie (cookie_name)
{
   var results = document.cookie.match ( '(^|;) ?' + cookie_name + '=([^;]*)(;|$)' );
   if ( results )
    	{
        return ( unescape ( results[2] ) );
      }else{
        return null;
      }
}