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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
本篇的内容到这里就全部结束了
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作者：Nian糕
链接：https://www.jianshu.com/p/dffa4ec4d452