Submit Drupal 8 webform via AJAX

Drupal8:Webforms:Ajax

<?php

function my_module_webform_submission_form_alter(array &$form, FormStateInterface $form_state, $form_id) {

    if ($form['#webform_id'] == 'contact_an_expert') {
        #$form['actions']['submit']['#validate'][] = 'wmp_content_types_contact_an_expert_form_validate';
        $form['actions']['submit']['#ajax'] = [
          'callback' => 'my_module_contact_an_expert_form_ajax',
          'wrapper' => '.field--name-dynamic-block-fieldnode-contact-an-expert-form',
          'type' => 'throbber',
        ];
    }
}

function my_module_contact_an_expert_form_ajax(&$form, FormStateInterface $form_state) {

    // Clear messages
    $messages = drupal_get_messages();

    // Check for validation errors
    $errors = $form_state->getErrors();

    if ($errors) {
        // Set error classes
        $form['elements']['first_name']['#attributes']['class'][] = 'custom-error-class';
    }
    else {
        // Output empty form for new submission
        _my_module_clear_webform_inputs($form, $form_state);
    }

    $response = new AjaxResponse();
    $response->addCommand(new HtmlCommand($form['actions']['submit']['#ajax']['wrapper'], $form));
    return $response;
}

function _my_module_clear_webform_inputs(array &$form, FormStateInterface $form_state) {

    $form_id = $form['#form_id'];
    $input = $form_state->getUserInput();
    $clean_keys = $form_state->getCleanValueKeys();
    
    // Remove input values
    $clean_keys[] = 'ajax_page_state';
    foreach ($input as $key => $item) {
        if (!in_array($key, $clean_keys) && substr($key, 0, 1) !== '_') {
            unset($input[$key]);
        }
    }
    $form_state->setUserInput($input);

    // Create new webform_submission entity
    $webform_submission = \Drupal\webform\Entity\WebformSubmission::create([
          'webform_id' => 'contact_an_expert',
    ]);

    // Create entity form object and link it with the webform_submission entity
    $entity_form_object = \Drupal::entityTypeManager()
        ->getFormObject('webform_submission', 'default');
    $entity_form_object->setEntity($webform_submission);

    // Set clean/new/without values form object to the current $form_state
    $form_state->setFormObject($entity_form_object);

    // Rebuild the form
    $form = Drupal::formBuilder()->rebuildForm($form_id, $form_state);
}