Automatically Populate Subject and Description Based on Drop-Down

Utilizing a custom JS listener on the "New Request Page" I want to listen for my "custom field" and set the subject and description based on the selection.  I think I can access this based on the following code and a case or select statement; can anyone tell me if i'm on the correct path.

custom_field_75567587.addEventListener('change', function() { 

     switch (custom_field_75567587.value){
          case conference_room:
          $('.form-field.request_subject').hide(); // Hide subject
          $('.form-field.request_description').hide(); // Hide description
          $('#request_subject').val('Conference Room Setup'); // autofill subject
          $('#request_description').val('test description'); // autofill description
     }

});