向Controller发送Ajax请求时出错，它不是json类型

Question

I am running Mojave / Laravel 5.8 / PHP 7.2 / Jquery.dataTables 10.1.19.

First round:
If I don't put: if (!$.fn.DataTable.isDataTable('.table')) {...
I got this error: DataTables warning: table id=DataTables_Table_0 - Cannot reinitialise DataTable.
I don't know exactly why, but I put this IF and it worked. I have other project where it works without that.

Second round:
In my index I call DataTable() that call an Ajax request to fill the table, so the Ajax URL is a route (from resource, created automatically) to a controller.
In my controller I have a function INDEX who will receive the request, but it needs to be checked if came from an Ajax request (the request must be a JSON) or from a view request.
I don't know why it always got a not Json type.
So, I got this error: DataTables warning: table id=DataTables_Table_0 - Invalid JSON response.

index.blade.php

            <div class="table-responsive">

               <table class="table table-bordered table-striped table-hover">
                    <thead>
                        <tr>
                            <th>Nome</th>
                            <th>NIF</th>
                            <th>Email</th>
                        </tr>
                    </thead>
                </table>
              </div>
            .
            .
            .
            <script type="text/javascript">   
               if (!$.fn.DataTable.isDataTable('.table')) {     
                  $('.table').DataTable({
                     "ajax": "{{ route('usuarios.index') }}",
                     "responsive": true,
                     "processing": true,
                     "serverSide": true,
                     "columns": [
                            { "data": "name" },
                            { "data": "nif" },
                            { "data": "email" },
                     ]
                  });
               };
            </script>   

UsuariosController.php

public function index(Request $request){ 
   if (request()->wantsJson()) {

       NEVER HERE 

       return ...

    }

    return view('admin.acesso.usuarios.index');
 }

Routes.php

Route::group(['prefix' => 'acesso'], function () {
    Route::resource('usuarios', "Acesso\UsuariosController");
});

Answer 1

error: DataTables warning: table id=DataTables_Table_0 - Cannot reinitialise DataTable.

You cannot reinitialize a data table. you have to destroy it.

if ($.fn.DataTable.isDataTable("#your_table")) {
  $('#mytable').DataTable().clear().destroy();
}

$("#your_table").dataTable({
     ...              
});

DataTables warning: table id=DataTables_Table_0 - Invalid JSON response.

means the response, does not contain all the specified data. in your code, you have the following

          "columns": [
                    { "data": "name" },
                    { "data": "nif" },
                    { "data": "email" },
             ]

your response, needs to have name, nig and email defined.

example

...
$dataRes = [
  [
      "name" => "test name",
      "nif" => "test nif",
      "email" => "test email",
  ],
    [
        "name" => "test name",
        "nif" => "test nif",
        "email" => "test email",
    ],
];

$response = [
    'data' => $dataRes,
    'draw' => $_POST['draw'], // this is from your param
    'recordsFiltered' => sizeof($dataRes), // this is if your using search
    'recordsTotal' => sizeof($dataRes),
];
return $response