koa2语法体验

//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