Change default format for date field on user register form

Question

I'm new to Drupal 8. In the user registration form, i've added a Date field via manage fields in user account settings. However, I need to customize this field and change its format. I tried 'manage display' but it's not taking effect. Is there something I'm missing. (Ideally, it should look and behave just like field datetime in Drupal 8 webform)

Appreciate any help given.

Thanks

Answer 1

You can implement template_preprocess_field() and alter the markup of the date field.

function MY_THEME_preprocess_field(&$vars) {
  if ($vars['field_name'] === 'field_custom_date_field') {
    $date_format = 'short'; // You need to provide the machine name of the format you want.
    $timestamp = strtotime($vars['element']['#items']->value);
    $markup = \Drupal::service('date.formatter')->format($timestamp, $date_format);
    $vars['items'][0]['content']['#text'] = $markup;
  }
}