读书笔记-es6Async函数栗子

async函数栗子

栗子一：从豆瓣 API 获取数据

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);
  }
})();

栗子二：根据电影文件名，自动下载对应的海报

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 ===');
})();