Adding AJAX to existing node in Drupal 7

To add AJAX to existing node (content type) in Drupal 7

Every Add/Edit node has a form_id. We can use that form_id to alter the form to AJAX handler to any form element.

To find form_id of node use Drupal's devel module (dpr() function) or simply just write print_r(form_id) in hook_form_alter() function.

To add AJAX handler to node form field write the following code in the hook_form_alter(&$form, &$form_state, $form_id)

$form['field_make'][LANGUAGE_NONE]['#ajax'] = array(

      'wrapper' => 'trailer-model',

      'callback' => 'smr_manage_trailer_populate_models_callback',

      'method' => 'replace',

      'progress' => array(

        'type' => 'throbber',

        'message' => "loading",

      ),

);

Here field_make is node form field in which we are adding AJAX.

Adding AJAX is same as we do in other custom form but here we add LANGUAGE_NONE after form field which is important for Add/Edit node form.