I’m trying to add an #ajax callback method to my views exposed form filter select box. But it seems the form have some issues with the callback. My code is pretty simple

/**  * Implements hook_form_FORM_ID_alter() for views_exposed_form.  */ function mymodule_form_views_exposed_form_alter(&$form, FormStateInterface $form_state) {   if ($form['#id'] == 'views-exposed-form-viewid') {     $op = ['hi' => 'hi', 'all' => 'all'];     $form['test'] = [       '#type' => 'select',       '#name' => 'test',       '#empty_option' => 'none',       '#options' => $op,       '#ajax' => [         'callback' => '_my_call',         'event' => 'change',         'wrapper' => 'edit-output-test',         'progress' => [           'type' => 'throbber',         ],       ],     ];      $form['callfield'] = [       '#type' => 'select',       '#options' => [],       '#prefix' => '<div id="edit-output-test">',       '#suffix' => '</div>',     ];   } }  function _my_call(array &$form, FormStateInterface $form_state) {   $response = new AjaxResponse();   $message = 'test';   $response->addCommand(new HtmlCommand('#edit-output-test', $message));   return $response;  } 

When I try to change the ‘test’ select box from view edit screen I get the below error

"SymfonyComponentHttpKernelExceptionHttpException: The specified #ajax callback is empty or not callable. in DrupalCoreFormFormAjaxResponseBuilder->buildResponse() (line 67 of /var/www/mypoc/docroot/core/lib/Drupal/Core/Form/FormAjaxResponseBuilder.php)."

When I change the filter from the front end I get the following error

"An unrecoverable error occurred. The uploaded file likely exceeded the maximum file size (32 MB) that this server supports."

And I see a lot of similar issues –

Ajax callback is not working on views exposed filters

Ajax submission leads to => An unrecoverable error occurred. The uploaded file likely exceeded the maximum file size (2 MB) that this server supports

Any working example would be great! Thanks.