app.js
const http = require('http')
const https = require('https')
const Koa = require('koa')
const app = new Koa()
app.use(ctx => {
ctx.body = 'Hello, World!'
})
app.listen(3000)
// http.createServer(app.callback()).listen(3000)
// https.createServer(app.callback()).listen(3000)