Ajax callback is not working on views exposed filters

Question

I am implementing dependent filters in views exposed filter for content:datasource search(Solr search). I have a requirement that in exposed dropdown field when a category is selected, by ajax i need to fetch the sub-categories and show up in another dropdown.For this I tried like below but its not going to callback function only. There is nothing logging in the network console also. Can anyone help me here to resolve.

use Drupal\Core\Ajax\AjaxResponse;
use Drupal\Core\Ajax\HtmlCommand;

function module_form_alter(&$form, &$form_state, $form_id) {
$form['field_categories']['#ajax'] = array(
        'callback' => 'module_get_subcategories',
        // 'callback' => '::module_get_subcategories',
        'event' => 'change',
        'wrapper' => 'edit-field-subcategory',
        'progress' => array(
          'type' => 'throbber',
          'message' => NULL,
        ),
      );
}


function module_get_subcategories(&$form, FormStateInterface $form_state) {
   $response = new AjaxResponse();
   $message = 'test';
   $response->addCommand(new HtmlCommand('#edit-field-subcategory', $message));
   return $response;
}

Answer 1

Something is weird in the code, What is that return statement in the last two lines?

For the ajax, try using $form['field_categories']['widget']['#ajax']

Make sure that you have cleared the cache too and that your module is actually called module.