var uri = "http://localhost/aniadir.php"
        $.ajax({
            url: uri,
            data: data,
            method: "POST",
            dataType:"json",
            async: true,

            success: function (response) {

                console.log("OK" + response.data.message);



            },
            error: function (xhr, textStatus, errorMessage) {

                console.log("ERROR" + errorMessage + textStatus + xhr);

            }
        }); // end ajax

$mysqli = new mysqli('localhost', 'root', 'error', 'tabla');

$jsondata["success"] = false;
$jsondata["data"] = array(
   'message' => $mysqli->error
);

 header('Content-type: application/json; charset=utf-8');
 echo json_encode($jsondata, JSON_FORCE_OBJECT);