middleOne 如何打印到 middleTwo await 之后的结果·· "express": "^4.18.2",

[cutemurphy2888]

const express = require('express'); const app = express();

const vv = { }

const middleOne = async (req, res, next) => { await next(); console.log(vv, 'middle1'); }

const haha = () => { return new Promise((resolve, reject) => { setTimeout(() => { resolve('hahahhahhah'); }, 3000); }) }

const middleTwo = async (req, res, next) => { const result = await haha(); vv.uname = result; console.log(vv, 3232); next(); }

app.use(middleOne); app.use(middleTwo);

app.get('/', (req, res, next) => { res.send({ 'cute': 'murphy' }); })

app.listen(3002, (res) => { console.log(res, 22); })

[zbinlin]

express 4 好像不支持 async function ，更新到 5 或者用 koa 吧

[cutemurphy2888]

@zbinlin 支持的 · 中间件 里面可以 await 一个异步结果·

[zbinlin]

@cutemurphy2888 可以用不代表支持呀，你这里就是打印不到 middleTwo await 之后的结果，就是因为 express 在调用 next() 时不是返回一个 promise ，导致你没办法 await 后一个 middleware 的 async 函数。

另外还有一个大问题就是这些 async 函数如果抛出异常的话，express 没办法捕获到

[zbinlin]

如果真的要用 async function ，可以这样用：

let resolve;
const promise = new Promise(r => {
resolve = r;
});

const middleOne = async (req, res, next) => {
next();
const vv = await promise;
console.log(vv, "middle1");
};

const haha = () => {
return new Promise((resolve, _reject) => {
setTimeout(() => {
resolve("hahahahah");
});
});
};

const middleTwo = async (req, res, next) => {
try {
const result = await haha();
resolve({
name: result,
});
next();
} catch (ex) {
next(ex);
}
};