How to detect which fields are being changed from a Business Rule in ServiceNow?

(function executeRule(current, previous /*null when async*/) {
     var dic = new GlideRecord('sys_dictionary');
     dic.addQuery('name=change_request^element!=NULL');
     dic.query(); 
     while (dic.next()) { 
       if (current[dic.element] != previous[dic.element] ) {
           gs.addInfoMessage (dic['name'] + '.' + dic.element + ' has changed!' ); 
       }   
     }
  })(current, previous);