Mine

function add_services(services) {
    var tmp = window.opener.document.gestion_services.services;
    var elements = services.split(",");
    for(i = 0; i < elements.length; i++) {
      if (document.getElementById('add_service_' + elements[i]).checked) {
        if (tmp.value)
          tmp.value += ',';
        tmp.value += elements[i];
      }
    }
    window.opener.document.gestion_services.submit();
    window.close();
  }