Seeing dpm or drupal set message when using AJAX


One of the worst head-aches you'll encounter with AJAX is the inability to know if the code you're writing works.


This is because there's no place for the drupal_set_message() or dpm() messages to show on the screen.


This is easily fixed by the code below: I included a complete working copy so you get a better sense of what is going on.
 * Implements hook_form_alter().
function hook_form_alter(&$form, &$form_state, $form_id) {

  // Check if ajax was fired.
  if (isset($form_state['triggering_element'])) {
    // We can do remote calls or execute Drupal
    // related functions.
    drupal_set_message(t('This will show within #message-container.'));

  $form['add_new_agency'] = array(
    '#type' => 'textfield',
    '#title' => t('Add new agency'),
    '#default_value' => '',
    '#ajax' => array(
      'callback' => 'add_new_agency_ajax_callback',
      'wrapper' => 'test-wrapper',
      '#prefix' => '<div id="test-wrapper">',
      '#suffix' => '</div>',
  // Create an area where the ajax callback can write Drupal
  // messages to.
  $form['message_area'] = array(
    '#type' => 'container',
    '#prefix' => '<div id="message-container">',
    '#suffix' => '</div>',

 * Ajax callback but more importantly, shows messages!
function add_new_agency_ajax_callback($form, $form_state) {
  $commands[] = ajax_command_remove('#message-area');
  $commands[] = ajax_command_after('#message-container', '<div id="message-area">' . theme('status_messages') . '</div>');

  return array('#type' => 'ajax', '#commands' => $commands);

Further Explanation

Notice line 27: $form['message_area'] array and line 37: add_new_agency_ajax_callback function.  Now if you use DPM or a drupal_set_message and your ajax is triggered, you'll see the results in $form['message_area'].

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