# Koa

# 什么是Koa？

# 为什么使用Koa？

# 基本使用

import Koa from 'koa'
const app = new Koa()

app.use(ctx => {
  ctx.body = 'Hello World'
})

app.listen(3000)

# 中间件

# 基本定义

module.exports = async function(ctx, next) {
  console.log('pv', ctx.path)
  await next()
}

# 常用中间件

koa-body
@koa/cors
koa-combine-routers
koa-compose
koa-helmet
koa-json
koa-router
koa-static

# koa-body

const koaBody = require('koa-body')
app.use(koaBody())
router.get('/', ctx => {
	console.log(ctx.request.body)
})

# koa-generator

npm i -g koa-generator
koa2 project

cd koa2-learn && npm install
npm run dev

# koa-router

const router = require('koa-router')()
router.prefix('/users')
router.get('/', async(ctx, next) => {
  ctx.body = "hello world"
})
return router

app.use(router.routes(), router.allowedMethods())

# cookie和session

ctx.cookies.set('pvid', Math.random())
ctx.cookies.get('pvid')

# 文件下载

router.get('/download', async (ctx) => {
  ctx.set({
    'Content-Type': 'application/octet-stream',
    'Content-Deposition': 'attachment;filename=FileName.txt',
  });

  const fileStream = fs.createReadStream(
    path.resolve(__dirname, '../file.txt')
  );

  ctx.body = fileStream;
});

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