如何查看“id”＃39;控制器中的值？

Question

我的javascript代码值将打印来自ajax响应的数据

<script type="text/javascript">
    function getval(get) {

        var id =  get.value;
        // alert(id);

        $.ajax({
            type : "POST",
            url :"http://localhost/codeIgniter/index.php/admin/ajax",
            data :{id:id},
            success:function(data){
                $('#sub_category').html(data);
                //window.location = "<?php echo site_url('admin/examdetails/form'); ?>"
            }
        });  
    }
</script>

控制器功能：将处理ajax请求

function ajax() 
{
    $id = $_POST['id'];
    echo "<script>";
    echo "alert(id);";
    echo "</script>";

    $this->load->model('admin_model');
    $query = $this->admin_model->get_sub_details($id);

    echo  '<select name="sub_category" id="sub_category">';

    foreach($query->result_array as $row)
    {                
        $name = $row['name']; 
        $id   = $row['id'];
        echo '<option value="'.$id.'">'$name'</option>';
    }
    echo '</select>';
}