es6学习笔记之Async函数的使用示例

var fetchDoubanApi = function() { 
 return new Promise((resolve, reject) => {
 var xhr = new XMLHttpRequest();
 xhr.onreadystatechange = function() {
  if (xhr.readyState === 4) {
  if (xhr.status >= 200 && xhr.status < 300) {
   var response;
   try {
   response = JSON.parse(xhr.responseText);
   } catch (e) {
   reject(e);
   }
   if (response) {
   resolve(response, xhr.status, xhr);
   }
  } else {
   reject(xhr);
  }
  }
 };
 xhr.open('GET', 'https://api.douban.com/v2/user/aisk', true);
 xhr.setRequestHeader("Content-Type", "text/plain");
 xhr.send(data);
 });
};
(async function() {
 try {
 let result = await fetchDoubanApi();
 console.log(result);
 } catch (e) {
 console.log(e);
 }
})();

import fs from 'fs';
import path from 'path';
import request from 'request';
var movieDir = __dirname + '/movies',
 exts  = ['.mkv', '.avi', '.mp4', '.rm', '.rmvb', '.wmv'];
// 读取文件列表
var readFiles = function () {
 return new Promise(function (resolve, reject) {
  fs.readdir(movieDir, function (err, files) {
   resolve(files.filter((v) => exts.includes(path.parse(v).ext)));
  });
 });
};
// 获取海报
var getPoster = function (movieName) {
 let url = `https://api.douban.com/v2/movie/search?q=${encodeURI(movieName)}`;
 return new Promise(function (resolve, reject) {
  request({url: url, json: true}, function (error, response, body) {
   if (error) return reject(error);
   resolve(body.subjects[0].images.large);
  })
 });
};
// 保存海报
var savePoster = function (movieName, url) {
 request.get(url).pipe(fs.createWriteStream(path.join(movieDir, movieName + '.jpg')));
};
(async () => {
 let files = await readFiles();
 // await只能使用在原生语法
 for (var file of files) {
  let name = path.parse(file).name;
  console.log(`正在获取【${name}】的海报`);
  savePoster(name, await getPoster(name));
 }
 console.log('=== 获取海报完成 ===');
})();