Use AJAX On Node Add Form To Change Field Required Status

On a node/add form I have a pair of fields that need to be able to control one another. The first field allows a user to enter a birthdate, the second field allows the user to say the birthdate is unknown.

I have attempted to work with Conditional Fields to make this work but I think for my case AJAX would be better.

If the birthdate_unkown field is not checked then the birthdate field should be required. When the birthdate_unkown field is checked then I would like to be able to make it so that the field is no longer required.

I have a working AJAX callback function I just cannot figure out how to use AJAX to change if the field is required or not.

I have tried options like:

$response->addCommand(new InvokeCommand('edit-field-birthdate-0-value-date','attr',['required', false]));

or

$response->addCommand(new InvokeCommand('edit-field-birthdate-0-value-date','removeAttr',['required']));

I have this code in a function that looks like this:

function _custom_field_unknown_birthday_logic(&$form, FormStateInterface $form_state) {
    \Drupal::logger('custom')->error('Unknown Birthday Callback');
    $values = $form_state->getValues();
    $unknown_birthdate = $values['field_unknown_birthdate']['value'];
    \Drupal::logger('custom')->error('Unknown Birthday Callback Value '. $unknown_birthdate);

    $response = new AjaxResponse();
    if ($unknown_birthdate == false) {
        $response->addCommand(new InvokeCommand('edit-field-birthdate-0-value-date','attr',['required']));
        \Drupal::logger('custom')->error('Birthdate IS required');
    } else if ($unknown_birthdate == true) {
        $response->addCommand(new InvokeCommand('edit-field-birthdate-0-value-date','removeAttr',['required'] ));
        \Drupal::logger('custom')->error('Birthdate IS NOT required');
    } else {
        \Drupal::logger('custom')->error('No Change to Birthdate');
    }
    return $response;
}

With the extensive logging I am doing I can see that I am getting to the right places in the code to issue the AJAX commands. That said the AJAX commands do not appear to change anything. I do not see anything in the console for Dev Tools either.

Any help on figuring out how to do this with AJAX is greatly appreciated. Once I get this working with AJAX there is more that needs to be accomplished that will not work with just States API.

Thanks!

Changes to the form must be made in the form definition, and cannot be made in the ajax callback, as Drupal has already cached the form by the point of the ajax callback, so even if you figured out a way to remove the required attribute on the field in the ajax callback, Drupal would reject a missing value as the form cache from before the ajax callback will still have the form field marked as required.

Instead, in your form definition (not the #ajax callback), you likely want some version of this:

if ($form_state->getValue('field_unknown_birthdate')) {
  unset($form['field_birthday_value']['widget']['#required']);
}

Note that I am guessing the location of the #required key, as well as the field names, so you'll have to inspect the actual $form object to determine the array in which the #required key is set, and unset it.