동시성(Concurrency)

Callback 보단 Promise 사용,
Promise 보단, async / await 사용 !!

결국엔 async / await 사용 추천

1. Callback

require('request').get('https://en.wikipedia.org/wiki/Robert_Cecil_Martin', (requestErr, response) => {
  if (requestErr) {
    console.error(requestErr);
  } else {
    require('fs').writeFile('article.html', response.body, (writeErr) => {
      if (writeErr) {
        console.error(writeErr);
      } else {
        console.log('File written');
      }
    });
  }
});

2. Promise

require('request-promise').get('https://en.wikipedia.org/wiki/Robert_Cecil_Martin')
  .then((response) => {
    return require('fs-promise').writeFile('article.html', response);
  })
  .then(() => {
    console.log('File written');
  })
  .catch((err) => {
    console.error(err);
  });

3. Async/Await

async function getCleanCodeArticle() {
  try {
    const response = await require('request-promise').get('https://en.wikipedia.org/wiki/Robert_Cecil_Martin');
    await require('fs-promise').writeFile('article.html', response);
    console.log('File written');
  } catch(err) {
    console.error(err);
  }
}