code: function tryServeWithBrotli(shouldTryGzip) {
        fs.stat(brotliFile, (err, stat) => {
          if (!err && stat.isFile()) {
            file = brotliFile;
            serve(stat);
          } else if (shouldTryGzip) {
            tryServeWithGzip();
          } else {
            statFile();
          }
        });
      }
docs: serve brotli file if exists, otherwise try gzip