[TOC] ### Koa2 中间件 ``` import Koa from 'koa'; const app = new Koa(); // 中间件1 app.use(async (ctx, next) => { console.log('1') await next() console.log('5') }) // 中间件2 app.use(async (ctx, next) => { console.log('2') await next() console.log('4') }) // 中间件3 app.use(async (ctx, next) => { console.log('3') }) app.listen(3000) ``` >[danger] 执行结果 1 2 3 4 5 中间件执行顺序为洋葱模型