新手起步可以参考

http://www.jianshu.com/p/6b816c609669

安装完后app.js大概是这样的，其中一些插件是我另外安装的

const Koa = require('koa')const views = require('koa-views')const json = require('koa-json')const onerror = require('koa-onerror')const bodyparser = require('koa-bodyparser')const logger = require('koa-logger')const cors = require('koa2-cors');const index = require('./routes/index')const users = require('./routes/users')const app = new Koa()// error handleronerror(app)//跨域插件app.use(cors())// middlewaresapp.use(bodyparser({  enableTypes:['json', 'form', 'text']}))app.use(json())app.use(logger())//静态文件引用app.use(require('koa-static')(__dirname + '/public'))//模板，pug后缀app.use(views(__dirname + '/views', {  extension: 'pug'}))// loggerapp.use(async (ctx, next) => {  const start = new Date()  await next()  const ms = new Date() - start  console.log(`${ctx.method} ${ctx.url} - ${ms}ms`)})// routes// allowedMethods()当前接口运行的methodsapp.use(index.routes(), index.allowedMethods())app.use(users.routes(), users.allowedMethods())// error-handlingapp.on('error', (err, ctx) => {  console.error('server error', err, ctx)});module.exports = app