//koa2：使用es678同步写法解决异步问题，相比于express解决了callback hell问题
const Koa = require("koa") // npm 安装最新版koa
const app = new Koa() // koa2创建server是通过new的方式
const asyncIO = ()=>{
return new Promise(resolve => setTimeout(resolve,500))
}
const mid = ()=> async (ctx,next)=>{
ctx.body = "mark"
await next()
ctx.body += "done"
}
app.use(mid())
app.use(async (ctx,next) => {
await asyncIO()
ctx.body += "saved"
await next()
})
app.listen(3000)
// 输出：mark saved done
