code: function callResponseMiddleware(err, res1, res2) {
          i -= 1;
          if (i >= 0) {
              var next = self.middlewares[i].response;
              if (typeof next === 'function') {
                  next(req, err, res1, res2, callResponseMiddleware);
              } else {
                  // skip this middleware if it doesn't implement response
                  callResponseMiddleware(err, res1, res2);
              }
          } else {
              callback(req, err, res1, res2);
          }
      }
docs: This function call the next response middleware in the stack until there are none left; in that case the callback is called instead, and the middleware run is completed.