Для сбора _ym_uid из cookies

   var ym_uid = getCookie('_ym_uid');
   function getCookie(name) {
     var matches = document.cookie.match(new RegExp(
       "(?:^|; )" + name.replace(/([\.$?*|{}\(\)\[\]\\\/\+^])/g, '\\$1') + "=([^;]*)"
     ));
     return matches ? decodeURIComponent(matches[1]) : undefined;
   }