Функция обещания

const promisify = func => (…args) =>
  new Promise((resolve, reject) =>
    func(…args, (err, result) => (err ? reject(err) : resolve(result)))
  );

const delay = promisify((d, cb) => setTimeout(cb, d));
delay(2000).then(() => console.log('Hi!')); // Promise resolves after 2s