Add a text field value with AJAX

Question

Problem: After an AJAX callback, the text is not inserted in the body field.

Description: I created a fresh Drupal installation. Added a field 'Type' | field_type | List (text) to the Article CT. The goal was that a change in that select would add text to the body field. Here's the ajax_test.module code, inspired by the documentation:

use Drupal\Core\Form\FormStateInterface;

/**
 * Implements hook_form_alter()
 */
function ajax_test_form_alter(&$form, \Drupal\Core\Form\FormStateInterface $form_state, $form_id) {
  if ($form_id === 'node_article_form') {

    $form['body']['#prefix'] = '<div id="edit-body-wrapper">';
    $form['body']['#suffix'] = '</div>';

    $form['field_type']['widget']['#ajax'] = [
      'callback' => 'myAjaxCallback',
      'disable-refocus' => FALSE,
      'event' => 'change',
      'wrapper' => 'edit-body-wrapper',
      'progress' => [
          'type' => 'throbber',
          'message' => t('Updating'),
      ],
    ];
  }
  // Outside the AJAX callback, the default_value works
  // $form["body"]["widget"][0]["#default_value"] = 'test';
}


function myAjaxCallback(array &$form, FormStateInterface $form_state) {
  if ($selectedValue = $form_state->getValue('field_type')) {
    $form["body"]["widget"][0]["#default_value"] = 'test';
    // Here it won't
  }
  return $form['body'];
}

If I set the default_value without the AJAX, it appears correctly. Using Xdebug, I can see that the callback is updating the value correctly, but nothing appears in the body on completion.

Any suggestions would be very appreciated.

Answer 1

I finally found out a solution here: AJAX form - replacing #default_value not working (the '2021 edit...') In this specific case, the callback would work:

function myAjaxCallback(array &$form, FormStateInterface $form_state) {
if ($selectedValue = $form_state->getValue('field_type')) {
    $userInput = $form_state->getUserInput();
    unset($userInput["body"]);
    $form_state->setUserInput($userInput);
    $form["body"]["widget"][0]["#default_value"] = 'test';
  }