disable all value of a multiple select when one is selected, then set a null value to the following field

I have a dynamic form using Ajax and javascript on my Symfony project.

I have a multiple select. I would like in this multiple select when I choose the value 7 which is "outside", all other value of this multiple select are disabled and unselectabled.

Here's the code for the scripts:

function checkOption(obj) {
        var select = document.getElementById("mySpace_databasebundle_zonestechnique_batiments");
        select.disabled = obj.value == "7";
      }

And this is the code for the twig view. Just know that I'am using a collection, i-e a formType in my Symfony project for make this form:

<div>
                {{ form_label(form.categorieszonestechnique, "Categorie(s) de la zone technique:", {'label_attr': {'class': 'control-label'}}) }}
                {{ form_errors(form.categorieszonestechnique) }}
                {{ form_widget(form.categorieszonestechnique, {'attr': {'class': 'selectpicker categories', 'onChange': 'checkOption(this)'}}) }}
              </div>

              <div>
                {{ form_label(form.batiments, "Appartenant au bâtiment:", {'label_attr': {'class': 'control-label'}}) }}
                {{ form_errors(form.batiments) }}
                {{ form_widget(form.batiments, {'attr': {'class': 'form-control', 'option selected': '--choose abâtiment--'}}) }}
              </div>

So when I selected the option 7, i-e "outside", I would like to disable all other value of the multiple select (selectpicker) and make them unselectabled. Then make a default value (null value) to the following field for the select tag of "batiments".

The id for the multiple select (selectpicker) is mySpace_databasebundle_zonestechnique_categorieszonestechnique and the id for the select tag of batiments is mySpace_databasebundle_zonestechnique_batiments. So, the javascript code works like with basic html for creating events, but I didn't find yet the solution to create these events.

Thank you in advance.