Mastering Drupal 8

Using AJAX

Many of the AJAX functions in Drupal 8 are very similar to how they were handled in Drupal 7. The major difference is in how the actual callbacks are triggered. Since forms are now classes, the #submit and #ajax attributes need to have callable values instead of just function names. As an example, let's take the configuration form from earlier and allow users to add multiple URLs. The first thing we do is to construct the wrapper around our list of URLs:

 public function buildForm(array $form, FormStateInterface $form_state) { $config = $this->config('mastering_drupal_8.settings'); $form['vals'] = array( '#type' => 'details', '#title' => $this->t('Rows'), '#open' => TRUE, ); // Wrapper around rows $form['vals']['rows'] = array( ...