https://chenshenhai.github.io/koa2-note/note/route/koa-router.html
https://jspang.com/detailed?id=34#toc23
#开始 ###基本命令：
npm init -y
npm install --save koa
node xxx.js
###基本文件
const Koa = require('koa')
const app = new Koa()
app.use( async ( ctx ) => {
ctx.body = 'hello koa2'
})
app.listen(3000)
console.log('[demo] start-quick is starting at port 3000')
#插件，中间件
###koa-bodyparser, 处理url
npm install --save koa-bodyparser@3
const bodyParser = require('koa-bodyparser');
app.use(bodyParser());
###koa-router路由 ###koa-cookies ###koa-static（中
###koa-ejs