代码整洁之道——7、并发

一、使用Promise,别使用Callbacks

Callbacks不够简洁，它会产生大量的嵌套。在ES6中，最好使用Promises

Bad:
import { get } from 'request';
import { writeFile } from 'fs';

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

Good:
import { get } from 'request';
import { writeFile } from 'fs';

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

 二、Async/Await 比Promises更简洁

Promises比callbacks简洁很多，但 ES2017/ES8 提出了async/await 方法，提供了更简洁的解决办法。你只需要在函数前面加一个 async关键字，然后就可以不用then链式方法写逻辑了。如果能用 ES2017/ES8现在就开始用吧。

Bad:
import { get } from 'request-promise';
import { writeFile } from 'fs-promise';

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

Good:
import { get } from 'request-promise';
import { writeFile } from 'fs-promise';

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