getAjaxAttributes example

'delta' => $delta,
          'region' => $region,
        ]);
      }
      if (isset($url)) {
        $build['add_block'] = [
          '#type' => 'link',
          '#url' => $url,
          '#title' => $this->t('Create @entity_type', [
            '@entity_type' => $this->entityTypeManager->getDefinition('block_content')->getSingularLabel(),
          ]),
          '#attributes' => $this->getAjaxAttributes(),
          '#access' => $this->currentUser->hasPermission('create and edit custom blocks'),
        ];
        $build['add_block']['#attributes']['class'][] = 'inline-block-create-button';
      }
    }

    $build['filter'] = [
      '#type' => 'search',
      '#title' => $this->t('Filter by block name'),
      '#title_display' => 'invisible',
      '#size' => 30,