Unsplash
Async 函数作为异步解决方案的最优解，async/await 特性能让我们编写出相比回调地狱和 Promise 链式调用更直观、更容易理解的代码，Async 函数返回一个 Promise 对象，可以使用 then() 方法添加回调函数，当函数执行的时候，一旦遇到 await 就会先返回，等到异步操作完成，再接着执行函数体内后面的语句
01 初识 async/await
const fetch = require('node-fetch');
async function JianShuRequest(id) {
const url = `https://www.jianshu.com/users/b0c7095032f3/collections_and_notebooks?slug=${id}`,
request = await fetch(url),
data = await request.json();
console.log(`bookname: ${data.notebooks[4].name}`);
}
JianShuRequest('b0c7095032f3')
运行结果
02 将 Async 函数用在 Promise 链中
const fetch = require('node-fetch');
async function JianShuRequest(id) {
const url = `https://www.jianshu.com/users/b0c7095032f3/collections_and_notebooks?slug=${id}`,
request = await fetch(url);
return await request.json();
}
JianShuRequest('b0c7095032f3').then(data => {
console.log(`bookname: ${data.notebooks[4].name}`);
})
运行结果
03 使用 await 进行调用
const fetch = require('node-fetch');
async function JianShuRequest(id) {
const url = `https://www.jianshu.com/users/b0c7095032f3/collections_and_notebooks?slug=${id}`,
request = await fetch(url);
return await request.json();
}
(async () => {
const data = await JianShuRequest('b0c7095032f3');
console.log(`bookname: ${data.notebooks[4].name}`);
})()
const fetch = require('node-fetch');
async function JianShuRequest(id) {
const url = `https://www.jianshu.com/users/b0c7095032f3/collections_and_notebooks?slug=${id}`,
request = await fetch(url);
return await request.json();
}
var bookname = async () => {
const data = await JianShuRequest('b0c7095032f3');
console.log(`bookname: ${data.notebooks[4].name}`);
}
bookname()
运行结果
04 await 并行
通过移动 await 关键词的位置实现多个 await 操作串行或者并行
const fetch = require('node-fetch');
async function JianShuRequest(id) {
const url = `https://www.jianshu.com/users/b0c7095032f3/collections_and_notebooks?slug=${id}`,
request = await fetch(url);
return await request.json();
}
var bookname = async () => {
console.time('time');
const data_1 = await JianShuRequest('b0c7095032f3');
const data_2 = await JianShuRequest('b0c7095032f3');
console.log(`bookname: ${data_1.notebooks[2].name}`);
console.log(`bookname: ${data_2.notebooks[4].name}`);
console.timeEnd('time');
}
bookname()
运行结果
const fetch = require('node-fetch');
async function JianShuRequest(id) {
const url = `https://www.jianshu.com/users/b0c7095032f3/collections_and_notebooks?slug=${id}`,
request = await fetch(url);
return await request.json();
}
var bookname = async () => {
console.time('time');
const dataPromise_1 = JianShuRequest('b0c7095032f3');
const dataPromise_2 = JianShuRequest('b0c7095032f3');
const data_1 = await dataPromise_1;
const data_2 = await dataPromise_2;
console.log(`bookname: ${data_1.notebooks[2].name}`);
console.log(`bookname: ${data_2.notebooks[4].name}`);
console.timeEnd('time');
}
bookname()
运行结果
根据两种方式得到的数据对比，并行所运行的时间更短，其主要思路是，先触发所有的请求，得到 Promise 对象，再通过 await 等待 resolve 返回的结果
05 使用 try catch 捕捉错误
const fetch = require('node-fetch');
async function JianShuRequest(id) {
const url = `https://www.jianshu.com/users/b0c7095032f3/collections_and_notebooks?slug=${id}`,
request = await fetch(url);
if(request.status != 200) {
throw new Error(request.statusText);
}
return await request.json();
}
const showJianShuRequest = async (id) => {
try {
const data = await JianShuRequest(id);
console.log(`bookname: ${data.notebooks[4].name}`);
}catch (err) {
console.error(err);
}
}
showJianShuRequest('666666');
运行结果
06 使用 Promise.all() 实现多个异步操作的并行
const fetch = require('node-fetch');
async function JianShuRequest(id) {
const url = `https://www.jianshu.com/users/b0c7095032f3/collections_and_notebooks?slug=${id}`,
request = await fetch(url);
return await request.json();
}
const showJianShuRequest = async () => {
const [data_1, data_2] = await Promise.all([
JianShuRequest('b0c7095032f3'),
JianShuRequest('b0c7095032f3'),
])
console.log(`bookname_1: ${data_1.notebooks[2].name}`);
console.log(`bookname_2: ${data_2.notebooks[4].name}`);
}
showJianShuRequest();
运行结果
07 在循环中正确使用 await
const fetch = require('node-fetch'),
bluebird = require('bluebird');
async function JianShuRequest(id) {
await bluebird.delay(1000);
const url = `https://www.jianshu.com/users/b0c7095032f3/collections_and_notebooks?slug=${id}`,
request = await fetch(url);
return await request.json();
}
const showJianShuRequest = async () => {
console.time('time');
const names = ['b0c7095032f3', 'b0c7095032f3'];
for(const name of names){
const data = await JianShuRequest(name);
console.log(`bookname_1: ${data.notebooks[2].name}`);
console.log(`bookname_2: ${data.notebooks[4].name}`);
}
console.timeEnd('time');
}
showJianShuRequest();
运行结果
const fetch = require('node-fetch'),
bluebird = require('bluebird');
async function JianShuRequest(id) {
await bluebird.delay(1000);
const url = `https://www.jianshu.com/users/b0c7095032f3/collections_and_notebooks?slug=${id}`,
request = await fetch(url);
return await request.json();
}
const showJianShuRequest = async () => {
console.time('time');
const names = ['b0c7095032f3', 'b0c7095032f3'];
const promises = names.map(x => JianShuRequest(x))
for (const promise of promises) {
const data = await promise;
console.log(`bookname_1: ${data.notebooks[2].name}`);
console.log(`bookname_2: ${data.notebooks[4].name}`);
}
console.timeEnd('time');
}
showJianShuRequest();
运行结果
参考资料
ECMAScript 6 入门——async 函数
玩转异步 JS ：async/await 简明教程
三分钟学会用ES7中的Async/Await进行异步编程
本篇的内容到这里就全部结束了，源码我已经发到了 GitHub async-await 上了，有需要的同学可自行下载
End of File
行文过程中出现错误或不妥之处在所难免，希望大家能够给予指正，以免误导更多人，最后，如果你觉得我的文章写的还不错，希望能够点一下喜欢和关注，为了我能早日成为简书优秀作者献上一发助攻吧，谢谢！^ ^
网友评论