Answers for "An invalid form control with name='cars' is not focusable."

an invalid form control with name='' is not focusable

add novalidate in your form
Example:
<form action="" novalidate>
</form>

An invalid form control with name='' is not focusable.

if(document.getElementById('hidden_field_choice_selector_parent_element'.value==true){
    document.getElementById('hidden_field').removeAttribute("required");        
}