autogrow_textarea.module

<?php

use Drupal\Core\Field\FieldDefinitionInterface;
use Drupal\Core\Field\WidgetInterface;
use Drupal\Core\Form\FormStateInterface;

/**
 * Implements hook_field_widget_third_party_settings_form().
 */
function autogrow_textarea_field_widget_third_party_settings_form(WidgetInterface $plugin, FieldDefinitionInterface $field_definition, $form_mode, $form, FormStateInterface $form_state) {
  $element = [];

  if (in_array($plugin->getPluginId(), ['text_textarea', 'text_textarea_with_summary'])) {
    $element['autogrow_textarea'] = array(
      '#type' => 'details',
      '#title' => t('Autogrow'),
      '#open' => TRUE,
      '#tree' => FALSE,
    );
    $element['autogrow_textarea_enabled'] = array(
      '#type' => 'checkbox',
      '#title' => t('Enable autogrow'),
      '#default_value' => $plugin->getThirdPartySetting('autogrow_textarea', 'autogrow_textarea_enabled'),
      '#group' => 'autogrow_textarea',
    );
    $element['autogrow_textarea_min_height'] = array(
      '#type' => 'textfield',
      '#title' => t('Min height'),
      '#description' => t('The css min-height value the textarea may shrink to.'),
      '#default_value' => $plugin->getThirdPartySetting('autogrow_textarea', 'autogrow_textarea_min_height'),
      '#group' => 'autogrow_textarea',
    );
    $element['autogrow_textarea_max_height'] = array(
      '#type' => 'textfield',
      '#title' => t('Max height'),
      '#description' => t('The css max-height value the textarea may grow to.'),
      '#default_value' => $plugin->getThirdPartySetting('autogrow_textarea', 'autogrow_textarea_max_height'),
      '#group' => 'autogrow_textarea',
    );
  }
  return $element;
}

/**
 * Implements hook_field_widget_settings_summary_alter().
 */
function autogrow_textarea_field_widget_settings_summary_alter(&$summary, $context) {
  if (in_array($context['widget']->getPluginId(), ['text_textarea', 'text_textarea_with_summary'])) {
    if ($context['widget']->getThirdPartySetting('autogrow_textarea', 'autogrow_textarea_enabled')) {
      $summary[] = t('Autogrow enabled');
    }
  }
}

/**
 * Implements hook_field_widget_form_alter().
 */
function autogrow_textarea_field_widget_form_alter(&$element, FormStateInterface $form_state, $context) {
  if ($context['widget']->getThirdPartySetting('autogrow_textarea', 'autogrow_textarea_enabled', FALSE)) {
    $element['#attributes']['class'][] = 'autogrow-textarea';
    $element['#attached']['library'][] = 'autogrow_textarea/autogrow_textarea_behaviors';
    if($max_height = $context['widget']->getThirdPartySetting('autogrow_textarea', 'autogrow_textarea_max_height')){
      $element['#attributes']['data-autogrow-max'] = $max_height;
    }
    if ($min_height = $context['widget']->getThirdPartySetting('autogrow_textarea', 'autogrow_textarea_min_height')) {
      $element['#attributes']['data-autogrow-min'] = $min_height;
    }
  }
}