const app = require('express')();
    app.use((req, res, next) => {
        // 做一些事情。。。
        next();
    })

    app.get('/', (req, res, next) => {
        res.send('something content');
    })

    const Express = require('express');
    const app = new Express();
    const sleep = () => new Promise(resolve => setTimeout(function(){resolve(1)}, 2000));
    const port = 8210;
    function f1(req, res, next) {
      console.log('this is function f1....');
      next();
      console.log('f1 fn executed done');
    }
    
    function f2(req, res, next) {
      console.log('this is function f2....');
      next();
      console.log('f2 fn executed done');
    }
    
    async function f3(req, res) {
      console.log('f3 send to client');
      res.send('Send To Client Done');
    }
    app.use(f1);
    app.use(f2);
    app.use(f3);
    app.get('/', f3)
    app.listen(port, () => console.log(`Example app listening on port ${port}!`))

    this is function f1....
    this is function f2....
    f3 send to client
    f1 fn executed done
    f2 fn executed done

    const sleep = () => new Promise(resolve => setTimeout(function(){resolve()}, 1000))
    async function f3(req, res) {
        await sleep();
      console.log('f3 send to client');
      res.send('Send To Client Done');
    }

const Koa = require('koa');
const app = new Koa();
const sleep = () => new Promise(resolve => setTimeout(function(){resolve()}, 1000))
app.use(async (ctx, next) => {
    console.log('middleware 1 start');
    await next();
    console.log('middleware 1 end');
});
app.use(async (ctx, next) => {
    await sleep();
    console.log('middleware 2 start');
    await next();
    console.log('middleware 2 end');
});
app.use(async (ctx, next) => {
    console.log('middleware 3 start')
    ctx.body = 'test middleware executed';
})

app.use((req, res, next) => {
    // c 沒有定義
    const a = c;
});
// 錯誤處理中間件
app.use((err, req, res, next) => {
    if(error) {
        console.log(err.message);
    }
    next()
})
process.on("uncaughtException", (err) => {
    console.log("uncaughtException message is::", err);
})

app.use((req, res, next) => {
    // c 沒有定義
    try {
        setTimeout(() => {
            const a = c;
            next()
        }, 0)
    } catch(e) {
        console.log('異步錯誤，能catch到么？？')
    }
});
app.use((err, req, res, next) => {
    if(error) {
        console.log('這里會執(zhí)行么??', err.message);
    }
    next()
})
process.on("uncaughtException", (err) => {
    console.log("uncaughtException message is::", err);
})