--- /dev/null
+<?php
+
+namespace Drupal\action_form_ajax_test\Plugin\Action;
+
+use Drupal\Core\Access\AccessResult;
+use Drupal\Core\Action\ConfigurableActionBase;
+use Drupal\Core\Form\FormStateInterface;
+use Drupal\Core\Session\AccountInterface;
+
+/**
+ * Plugin used for testing AJAX in action config entity forms.
+ *
+ * @Action(
+ * id = "action_form_ajax_test",
+ * label = @Translation("action_form_ajax_test"),
+ * type = "system"
+ * )
+ */
+class ActionAjaxTest extends ConfigurableActionBase {
+
+ /**
+ * {@inheritdoc}
+ */
+ public function defaultConfiguration() {
+ return [
+ 'party_time' => '',
+ ];
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function access($object, AccountInterface $account = NULL, $return_as_object = FALSE) {
+ $result = AccessResult::allowed();
+ return $return_as_object ? $result : $result->isAllowed();
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function execute() {
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function buildConfigurationForm(array $form, FormStateInterface $form_state) {
+ $having_a_party = $form_state->getValue('having_a_party', !empty($this->configuration['party_time']));
+ $form['having_a_party'] = [
+ '#type' => 'checkbox',
+ '#title' => $this->t('Are we having a party?'),
+ '#ajax' => [
+ 'wrapper' => 'party-container',
+ 'callback' => [$this, 'partyCallback'],
+ ],
+ '#default_value' => $having_a_party,
+ ];
+ $form['container'] = [
+ '#type' => 'container',
+ '#prefix' => '<div id="party-container">',
+ '#suffix' => '</div>',
+ ];
+
+ if ($having_a_party) {
+ $form['container']['party_time'] = [
+ '#type' => 'textfield',
+ '#title' => $this->t('Party time'),
+ '#default_value' => $this->configuration['party_time'],
+ ];
+ }
+
+ return $form;
+ }
+
+ /**
+ * Callback for party checkbox.
+ */
+ public function partyCallback(array $form, FormStateInterface $form_state) {
+ return $form['container'];
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function submitConfigurationForm(array &$form, FormStateInterface $form_state) {
+ $this->configuration['party_time'] = $form_state->getValue('party_time');
+ }
+
+}