8个示例展示Async/Await

首先安装依赖

  "dependencies": {
    "bluebird": "^3.5.0",
    "node-fetch": "^1.7.2"
  }

bluebird是把回调方式改写成Promise方式
使用方法为

const Promise = require('bluebird')
const readFile = Promise.promisify(require("fs").readFile)

node-fetch是服务端使用的基于Promise的Ajax的请求方式
ok,可以开始了

1.基本使用

const fetch = require('node-fetch');

async function getZhihuColumn(id) {
  const url = `https://zhuanlan.zhihu.com/api/columns/${id}`;
  const response = await fetch(url);
  const column = await response.json();
  console.log(`NAME: ${column.name}`);
  console.log(`INTRO: ${column.intro}`);
}

getZhihuColumn('feweekly');

2.像promise那样使用

const fetch = require('node-fetch');

async function getZhihuColumn(id) {
  const url = `https://zhuanlan.zhihu.com/api/columns/${id}`;
  const response = await fetch(url);
  return await response.json();
}

getZhihuColumn('feweekly')
  .then(column => {
    console.log(`NAME: ${column.name}`);
    console.log(`INTRO: ${column.intro}`);
  });

3.在闭包中使用 await

const fetch = require('node-fetch');

const getZhihuColumn = async (id) => {
  const url = `https://zhuanlan.zhihu.com/api/columns/${id}`;
  const response = await fetch(url);
  return await response.json();
};

class APIClient {
  async getColumn(id) {
    const url = `https://zhuanlan.zhihu.com/api/columns/${id}`;
    const response = await fetch(url);
    return await response.json();
  }
}

(async () => {
  const client = new APIClient();
  const column = await client.getColumn('feweekly');
  // const column = await getZhihuColumn('feweekly');
  console.log(`NAME: ${column.name}`);
  console.log(`INTRO: ${column.intro}`);
})();

4.异常处理

const fetch = require('node-fetch');

async function getZhihuColumn(id) {
  const url = `https://zhuanlan.zhihu.com/api/columns/${id}`;
  const response = await fetch(url);
  if (response.status !== 200) {
    throw new Error(response.statusText);
  }
  return await response.json();
}

const showColumnInfo = async (id) => {
  try {
    const column = await getZhihuColumn(id);
    console.log(`NAME: ${column.name}`);
    console.log(`INTRO: ${column.intro}`);
  } catch (err) {
    console.error(err);
  }
};

showColumnInfo('feweekly123');

5.异步嵌套

const fetch = require('node-fetch');

const sleep = (timeout = 2000) => new Promise(resolve => {
  setTimeout(resolve, timeout);
});

async function getZhihuColumn(id) {
  await sleep(2000);
  const url = `https://zhuanlan.zhihu.com/api/columns/${id}`;
  const response = await fetch(url);
  return await response.json();
}

const showColumnInfo = async () => {
  console.time('feweekly');
  const feweekly = await getZhihuColumn('feweekly');
  console.log(`NAME: ${feweekly.name}`);
  console.log(`INTRO: ${feweekly.intro}`);
  console.timeEnd('feweekly');

  console.time('toolingtips');
  const toolingtips = await getZhihuColumn('toolingtips');
  console.log(`NAME: ${toolingtips.name}`);
  console.log(`INTRO: ${toolingtips.intro}`);
  console.timeEnd('toolingtips');
};

showColumnInfo();

6.多个异步同时（promise.all）

const fetch = require('node-fetch');

async function getZhihuColumn(id) {
  const url = `https://zhuanlan.zhihu.com/api/columns/${id}`;
  const response = await fetch(url);
  return await response.json();
}

const showColumnInfo = async () => {
  const [feweekly, toolingtips] = await Promise.all([
    getZhihuColumn('feweekly'),
    getZhihuColumn('toolingtips'),
  ]);

  console.log(`NAME: ${feweekly.name}`);
  console.log(`INTRO: ${feweekly.intro}`);

  console.log(`NAME: ${toolingtips.name}`);
  console.log(`INTRO: ${toolingtips.intro}`);
};

showColumnInfo();

7.任何返回Promise对象的函数（thenable）

const bluebird = require('bluebird');

async function main() {
  console.log('waiting...');
  await bluebird.delay(2000);
  console.log('done!');
}

main();

8.循环中异步

有点类似promise.all

const fetch = require('node-fetch');
const bluebird = require('bluebird');

async function getZhihuColumn(id) {
  await bluebird.delay(1000);
  const url = `https://zhuanlan.zhihu.com/api/columns/${id}`;
  const response = await fetch(url);
  return await response.json();
}

const showColumnInfo = async () => {
  console.time('showColumnInfo');

  const names = ['feweekly', 'toolingtips'];
  const promises = names.map(x => getZhihuColumn(x));
  for (const promise of promises) {
    const column = await promise;
    console.log(`Name: ${column.name}`);
    console.log(`Intro: ${column.intro}`);
  }

  console.timeEnd('showColumnInfo');
};

showColumnInfo();