我正在尝试使用json使用setdata方法更新morris.js图。在通过控制台显示json时，这看起来不错，但当我执行morris setdata时，它只接受未定义的值​​实际上，图表仍然是空白的

<script>
 var MagD = new Morris.Line({
 element : 'chart',
 data:[<?php echo $chart_data; ?>],
 xkey:'hora',
 ykeys:['mag'],
 labels:['magnitud'],
 hideHover:'auto',
 stacked:true,
 resize: true,
 parseTime: false
});
</script>
    <script>
$(document).ready(function(){
    $('#ActBtn').click(function(){
            $("#anoG option:selected").each(function () {
                    ano = $(this).val();           
                });
            $("#mesG option:selected").each(function () {
                    mes = $(this).val();           
               });
            $("#diaG option:selected").each(function () {
                    dia = $(this).val();
                     $.ajax({
                      type : 'POST',
                      dataType:'json',
                      url : 'getGrafica.php',
                      data : { mes: mes, ano: ano, dia:dia },
                      success: function(json){
                        var nuevaData = JSON.parse(JSON.stringify(json));
                        console.log(json);
                        MagD.setData(JSON.parse(JSON.stringify(nuevaData)));
                      },
                      error: function(json){
                        alert("Something went wrong, please refresh");
                      }
                        });
                       }); 
                        {
                    }); 
              });   
   </script>

我用于post方法的php如下

<?php
         $conexion=mysqli_connect('localhost','root','','luz');
         $ano = $_POST['ano'];
         $mes = $_POST['mes'];
         $dia = $_POST['dia'];
    $query = "SELECT * FROM sensor WHERE dia = $dia AND mes = $mes AND ano = $ano";
    $result = mysqli_query($conexion, $query);
    $chart_data = '';
    while($row = mysqli_fetch_array($result))
    {
     $chart_data .= "{ hora:'".$row["hora"]."', mag:".$row["magnitud"]."}, ";
    }
    $chart_data = substr($chart_data, 0, -2);
    $chart_data = json_encode("[".$chart_data."]");
    echo($chart_data)
    ?>

当我在控制台中检查json对象时，它会给我以下数据

[{ hora:'02:15:30', mag:15.05}, { hora:'02:26:31', mag:15.05}, { hora:'02:27:52', 
    mag:15.11}, { hora:'02:29:01', mag:15.28}]

然后是价值观​​我的图的属性仍然未定义，但它不会给我带来任何错误