callback.js

   for(j = 0; j < provinces.length; j++){
         
      var province = provinces[j];
      var province_name = _s.strLeft(province.provincia, '/');
      
      mongo_provinces[j] = {
           _id: new mongodb.ObjectID()
         , slug: _s.slugify(province_name)
         , name: province_name
         , country: "spain"
         , towns: []
      };

      var query = con.query('select * from municipios where id_provincia = ? order by nombre', [province.id_provincia], function(err, towns){ if(err) throw err;
          console.log(j);
      });
   }