ercore-8.x-1.20/modules/ercore_collaboration/ercore_collaboration.module

<?php

/**
 * @file
 * Hook implementations for the ERCore Collaborations module.
 */

use Drupal\Core\Form\FormStateInterface;
use Drupal\Core\Ajax\AjaxResponse;
use Drupal\Core\Ajax\CloseModalDialogCommand;

/**
 * Implements hook_form_alter().
 */
function ercore_collaboration_form_node_form_alter(&$form, FormStateInterface $form_state, $form_id) {
  if ($form_id === 'node_ercore_collaboration_edit_form' || $form_id === 'node_ercore_collaboration_form') {
    $form['#validate'][] = 'ercore_collaboration_node_form_validate';
  }
  // If institution node form.
  if ($form_id === 'node_ercore_institution_form') {
    $modal = \Drupal::request()->get('modal');
    // If Institution form is in modal.
    if (isset($modal) && $modal === 'true') {
      $form['actions']['submit']['#submit'][] = '_modal_form_institution_ajax_submit';
      $form['actions']['submit']['#attributes']['class'][] = 'use-ajax-submit';
      $form['#attached']['library'][] = 'ercore_collaboration/ercore-collaboration-modal.library';
    }
  }
}

/**
 * Custom validation hook.
 */
function ercore_collaboration_node_form_validate(&$form, FormStateInterface $form_state) {
  $value1 = $form_state->getValue('field_ercore_collaboration_start');
  $value2 = $form_state->getValue('field_ercore_collaboration_end');
  if (!empty($value2['0']['value']) && $value2['0']['value'] < $value1['0']['value']) {
    $form_state->setErrorByName('field_ercore_collaboration_end', t('End date must be after start date.'));
  }
}

/**
 * Close the Institution Modal and leave use on page.
 *
 * @param array $form
 *   The form that will be altered.
 * @param \Drupal\Core\Form\FormStateInterface $form_state
 *   FormState Object.
 */
function _modal_form_institution_ajax_submit(array $form, FormStateInterface &$form_state) {
  $response = new AjaxResponse();
  $response->addCommand(new CloseModalDialogCommand());
  $form_state->setResponse($response);
}