Javascript 仍在尝试理解mysql到json的数据

这个PHP应该返回4行数据。。。。 A行、B行、C行、D行

$query = $mysqli->query("select codeid,description from codeTable where tableCode='TABLE'");
$json = array();
if($query->num_rows){
    while($tblArray[] = $query->fetch_object()){
    $json[]=$tblArray;
    }
}
echo json_encode($json);

[[{"codeid":"4","description":"Document Type"}],[{"codeid":"4","description":"Document Type"},{"codeid":"8","description":"Images"}],[{"codeid":"4","description":"Document Type"},{"codeid":"8","description":"Images"},{"codeid":"1","description":"Note Type"}],[{"codeid":"4","description":"Document Type"},{"codeid":"8","description":"Images"},{"codeid":"1","description":"Note Type"},{"codeid":"5","description":"Projects"}]]

但事实上，json_encode显示了10行数据。。。。 A排， A排，B排， A行，B行，C行， A行、B行、C行、D行

$query = $mysqli->query("select codeid,description from codeTable where tableCode='TABLE'");
$json = array();
if($query->num_rows){
    while($tblArray[] = $query->fetch_object()){
    $json[]=$tblArray;
    }
}
echo json_encode($json);

[[{"codeid":"4","description":"Document Type"}],[{"codeid":"4","description":"Document Type"},{"codeid":"8","description":"Images"}],[{"codeid":"4","description":"Document Type"},{"codeid":"8","description":"Images"},{"codeid":"1","description":"Note Type"}],[{"codeid":"4","description":"Document Type"},{"codeid":"8","description":"Images"},{"codeid":"1","description":"Note Type"},{"codeid":"5","description":"Projects"}]]

有人能告诉我为什么会这样吗？最终目标是将查询返回的四行数据放入javascript数组。

同时（$json[]=$query->fetch_object（））继续；echo json_encode（$json）
// remove [] here, or you are adding the row data to an array, then add to another array.
while($tblArray = $query->fetch_object()){
   $json[] = $tblArray;
}