Show the checkout ID Card field only in certain states of a country

[kokonauta]

Hi, I need some help to achieve a customization on checkout address:

I want to show the ID Card field only on certain states of a specific country but i don't know how to work arround this.
The problem is that It can be configured the ID card field for the whole country, but not for certain states.

I think that is possible to make a conditional to show the field but I don't know how to check if is the desired country and states. Once solved this first part, the second problem is how to make the ajax call to update the field on a state change.

I would aprecciate any information to progress in that customization.

Thanks in advance.

[kokonauta]

I have achieved part of the desired with this code on order-opc.js
Now the field is visible on the specific states, and hidden on the other states

$('#id_state').on('change', function() {
        if($('#id_country').val() == 6){
            if( $('#id_state').val() == 339 || $('#id_state').val() == 351 || $('#id_state').val() == 363 || $('#id_state').val() == 364 ){
                $('.dni').show()
            }else{$('.dni').hide()}
        }
    })

 

Now the only problem is how to validate the field as required and output error when the field is not well filled. (The field is not required normally because all the other states not require fill the field)
 

Edited July 12, 2017 by kokonauta (see edit history)