Rest api add to select append sharepoint list is undefined

If alert view then OK, but is add code select append, not working - undefined Here is code:

function getListItemById(webUrl,listName, itemId, success, failure) {
    var url = webUrl + "/_vti_bin/listdata.svc/" + listName + "(" + itemId + ")";
    $.ajax({
        url: url,
        method: "GET",
        headers: { "Accept": "application/json; odata=verbose" },
        success: function (data) {
            success(data.d);
        },
        error: function (data) {
            failure(data.responseJSON.error);
        }
    });
}


getListItemById('http://sharepoint/','Task',1,function(taskItem){
    //alert(taskItem.Tabn);
    //alert(taskItem.Xul);
    //var Tabn = ($(this).attr(taskItem.Tabn));
    //var Tabn = taskItem.Tabn.toString();
    //alert(Tabn);
    //$("#State").val(taskItem.Tabn);
    $("#test").append(""+ $(this).attr(taskItem.title) + "");
  },
  function(error){
    console.log(JSON.stringify(error));
  }
);