在学习express和koa中间件的时候，我自己一直按照洋葱模型来理解。但是理论上他们是不一样的。

//express版本
var express = require('express');
var app = express();

app.use((req, res, next) => {
    setTimeout(() => {
        console.log('start1')
    })
    next();
    console.log('end1')
})
app.use((req, res, next) => {
    console.log('start2')
    next();
    console.log('end2');
})
app.use((req, res, next) => {
    console.log('start3');
    next();
    console.log('end3');
})

app.get('/', function (req, res) {
    console.log('before')
    res.send('Hello World!');
    console.log('after')
  });
  
app.listen(3000, function () {
    console.log('Example app listening on port 3000!');
});

koa版本

const Koa = require('koa');
const app = new Koa();

app.use(async (ctx, next) => {

    await new Promise((resolve, reject) => {
        setTimeout(() => {
            console.log('start1')
            resolve()
        })
    })
    await  next();
    console.log('end1')
})
app.use(async (ctx, next) => {
    console.log('start2')
    await  next();
    console.log('end2');
})
app.use(async (ctx, next) => {
    console.log('start3');
    await  next();
    console.log('end3');
})

app.use(ctx => {
    console.log('before');
    ctx.body = 'Hello Koa';
    console.log('after');
  });
  
app.listen(3001)

现在的问题是，如何修改上面的代码，就能明显区分出express和koa中间件作用机制的不同？