Ajax Form | Drupal 8

Ajax Form

Submitted by editor on Wed, 11/18/2015 - 16:48

How to Change a form using ajax ?

Exemple : Field 'username'

    $form['username'] = array(
      '#type' => 'textfield',
      '#title' => 'Your user name',
      '#description' => 'User name',
      '#ajax' => array(
        'callback' => '::checkUserNameAjax',
        'wrapper' => 'edit-username',
        'method' => 'replace',
        'effect' => 'fade',
        'event' => 'change',

      //If you want to change the ID
      '#prefix' => '<div id="edit-username">',
      '#suffix' => '</div>',

1. Ajax Methode to Edit Form
  function checkUserNameAjax($form, FormStateInterface $form_state) {
    $form['username']['#description'] = "YES";
    return $form['username'];

2. Or using AjaxResponse to change HTML/CSS

  function checkUserNameAjax(array &$form, FormStateInterface &$form_state) {
    $valid = rand(0,1);
    if ($valid) {
      $css = ['border' => '1px solid green'];
      $message = ('User name ok.');
    }else {
      $css = ['border' => '1px solid red'];
      $message = ('User name not valid.');
    $response = new \Drupal\Core\Ajax\AjaxResponse();
    $response->addCommand(new \Drupal\Core\Ajax\CssCommand('#edit-username', $css));
    $response->addCommand(new \Drupal\Core\Ajax\HtmlCommand('#edit-username--description', $message));
    return $response;

Example 2 : Change a title using selected value

public function buildForm(array $form, FormStateInterface $form_state) {
  $form['methods'] = array(
    '#type' => 'select',
    '#title' => $this->t('Method'),
    '#default_value' => "",
    '#options' => ["a"=>"A Value","b"=>"B Value",],
    '#ajax' => array(
      'callback' => '::methodChangeAjax',
      'wrapper' => 'edit-fieldsset',
      'method' => 'replace',
      'effect' => 'fade',
      'event' => 'change',
//Ajax changable fields container
  $form['fieldsset'] = array(
    '#type' => 'fieldset',
    '#title' => $this->t('Fields'),
    '#default_value' => "",
    '#prefix' => '<div id="edit-fieldsset">',
    '#suffix' => '</div>',
  return $form;
function methodChangeAjax($form, FormStateInterface $form_state) {
  $method = $form_state->getValue('methods');
  $form['fieldsset']['#title'] = $method;
  return $form['fieldsset'];


This happens if you add the fields on the callback function. The form doesn't get rebuilt at this point, so the values on the new fields are discarded. You need to add the fields on buildForm function by checking on the $form_state values.

On the simplest case, you can check that the triggering field has a value set and then conditionally build the new field as per defined functionality. Then on the callback you just need to call:

return $form['wrapper_of_the_element_to_change'];

WillBradley (not verified)

Tue, 07/17/2018 - 14:36

As a rule, there are two different ways to AJAX this form submit! That is, we present the form via AJAX and the server returns HTML. The AJAX would restore the form HTML with the blunder in it so we can render it on the page assignment help service. This is less demanding... since you don't have to do all that much in JavaScript. Be that as it may, this approach is also a bit outdated.

Salman Haider (not verified)

Mon, 04/29/2019 - 08:59

Dear Drupaler,

I have a scenario where I alter options of a form fields with ajax callbacks.
Like I have A, B, C, D fields (all dropdowns)

Selecting any option in field A filters down option for field B, which further filters options to a limited number on C and so on.

I have altered these options based on selections, using Ajax callbacks in Drupal8 and handled current value through $form_state and returning updated select lists with updated and filtered options through use Drupal\Core\Ajax\AjaxResponse;
use Drupal\Core\Ajax\ReplaceCommand;

Success: The form works great, screenshot: http://prntscr.com/ni5h0k
But the problem is when I submit the form, I get this error "An illegal choice has been detected. Please contact the site administrator."
Screenshot: http://prntscr.com/ni5he5

How do I get it to resolve and get this done?
Anyone who could help?

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