Dynamic form modification for CollectionField in EasyAdmin

Question

Purpose

I want to create a simple CMS based on EasyAdmin 4, where a user can build articles made of different content types, f.e. wysiwygs, galleries, quotations and others. It kind of works, but lacks a dynamic (ajax) approach for it.

Current code

I am building my FormType using this approach. For simplicity, there are just 2 types of content - wysiwyg and horizontal line.

In CRUD controller, there is this:

public function configureFields(string $pageName): iterable
{
    return [
        TextField::new('title'),
        CollectionField::new('content')
            ->setEntryType(ArticleContentType::class),
    ];
}

And in ArticleContentType, there is this:

public function buildForm(FormBuilderInterface $builder, array $options): void
{
    $builder
        ->add('type', ChoiceType::class, [
            'choices' => [
                'WYSIWYG Editor' => 'wysiwyg',
                'Horizontal line' => 'horizontal_line',
            ],
        ])
    ;

    $formModifier = function (FormInterface $form, $data = null) {
        if (is_array($data) && $data['type'] === 'wysiwyg') {
            $form->add('wysiwyg', TextareaType::class);
        }
    };

    $builder->addEventListener(
        FormEvents::PRE_SET_DATA,
        function (FormEvent $event) use ($formModifier) {
            $data = $event->getData();
            $formModifier($event->getForm(), $data);
        }
    );

    $builder->get('type')->addEventListener(
        FormEvents::POST_SUBMIT,
        function (FormEvent $event) use ($formModifier) {
            $type = $event->getForm()->getData();
            $formModifier($event->getForm()->getParent(), $type);
        }
    );
}

The problem

Solution above works, but only after saving an article (it shows wysiwyg when I select a WYSIWYG Editor option). Now I need to use some JavaScript to add the wysiwyg without saving/refreshing the article. I tried (as in the mentioned documentation) something like this:

fetch(document.getElementById('new-Article-form').action, {
  method: "POST",
  body: new FormData(document.getElementById('new-Article-form')),
}).then((r) => r.text())

but it fails in EasyAdmins's AbstractCrudController (Undefined array key "ea").

Is there anyone who managed to do this? Can somebody point me in the right direction?

Thank you.