refactoring-nodejs-router.js

router.get(url, function (req, res) {
  function handleSuccess (file) {
    res.writeHead(200, { "Content-Type": "application/octet-stream" });
    res.write(file);
    res.end();
  }
  function handleError (err) {
    res.writeHead(404);
    res.end();
  }
  const callback = higherOrderNodeCallback(handleSuccess, handleError);
  readFile(filePath, callback);
});