Basic usage of Koa framework

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前言（来自官网）

ES6/7 带来的变革
自ES6确定和ES7的async/await开始普及,node.jsdevelopment has become more rapid,可以预见到JavaScriptModerately“头疼”Multiple levels of nested callbacks（注意是”多层嵌套回调“）将会使用Promise + async/await的方式逐渐替代（不是完全替代,Multi-layer nested callbacks also have their special application scenarios）.
koa2 The trend of the future
基于async/awaitrealize the intermediate systemkoa2The frame will benode.js webThe development direction of the general trend of the popular framework.基于generator/yield的koa1will be gradually removedkoa2替代,毕竟使用co.js来处理generatorIt's a way of transition,Although it has its specific application scenarios,但是用async/awaitSynchronous writing will be implemented more elegantly.

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一、Koa是什么？

Koa2 是基于 node.js web serve 框架
koaThe registered middleware provides two parameters,即ctx/next.ctx是req和res的集合;next()is to execute the next middleware.

二、Koa的安装

1.项目初始化

npm init -y  // 生成package.json文件

2.安装Koa2

npm install koa --save

3.Hello world

const Koa = require('koa')  // 导入Koa
const app = new Koa()  // 实例化app对象

app.use( async ( ctx ) => {  // 编写中间件
  ctx.body = 'Hello world'
})

app.listen(3000)  // 启动服务
console.log('[demo] start-quick is starting at port 3000')

4.启动Demo

node index.js  // 访问http:localhost:3000

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三、中间件

A process-independent business module,可扩展、可插拔.简单来说,It is to split complex business into independent functions,就是中间件.
包含但不限于：
1、npm install koa-router 路由库

const Koa = require('koa');
const Router = require('koa-router'); // 导入koa-router中间件

const app = new Koa();
const userRouter = new Router({
     prefix: '/user' }); // 属性前缀

userRouter.get('/test', (ctx, next) => {
    
    ctx.response.body = "test request"
    // console.log(ctx.params.id)
});

userRouter.post('/', (ctx, next) => {
    
    ctx.response.body = "test response"
});

app
	// .use((ctx, next) => {
    
    // ctx.body = ctx.request.query
    // })
    .use(userRouter.routes())  //注册为中间件
    .use(userRouter.allowedMethods())  //用于判断某一个 method 是否支持,Method Not Allowed

app.listen(3000, () => {
    
    console.log("dome is start")
})

获取params参数：

userRouter.get('/test/:id', (ctx, next) => {
    
    ctx.response.body = "test request"
    console.log(ctx.params.id)
});

获取query参数：

.use((ctx, next) => {
    
    ctx.body = ctx.request.query
})

实现二级路由：

const Koa = require('koa')
const fs = require('fs')
const app = new Koa()

const Router = require('koa-router')

let home = new Router()

// 子路由1
home.get('/', async ( ctx )=>{
    
  let html = ` <ul> <li><a href="/page/helloworld">/page/helloworld</a></li> <li><a href="/page/404">/page/404</a></li> </ul> `
  ctx.body = html
})

// 子路由2
let page = new Router()
page.get('/404', async ( ctx )=>{
    
  ctx.body = '404 page!'
}).get('/helloworld', async ( ctx )=>{
    
  ctx.body = 'helloworld page!'
})

// 装载所有子路由
let router = new Router()
router.use('/', home.routes(), home.allowedMethods())
router.use('/page', page.routes(), page.allowedMethods())

// 加载路由中间件
app.use(router.routes()).use(router.allowedMethods())

app.listen(3000, () => {
    
  console.log('[demo] route-use-middleware is starting at port 3000')
})

2、npm install koa-bodyparser 解析json数据

const Koa = require('koa')
const bodyParser = require('koa-bodyparser') // 导入koa-bodyparser中间件
const app = new Koa()

app.use(bodyParser())  // 使用ctx.body解析中间件

app.use(async (ctx) => {
    
    if (ctx.url === '/' && ctx.method === 'GET') {
    
        const html = ` <form method="POST" action="/"> <label for="forName" >Name</label> <input id="forName" type="text" name="name"></input> <button type="submit">submit</button> </form> `
        ctx.body = html
    } else if (ctx.url === '/' && ctx.method === 'POST') {
    
        ctx.body = ctx.request.body  //关键句,koa-bodyparser解析POST表单里的数据,为json类型
    } else {
    
        ctx.body = "<h1>404 Not Found</h1>"
    }
})

app.listen(3000)
console.log('[demo] start-quick is starting at port 3000')

四、洋葱模式

在洋葱模型中,当我们执行第一个中间件时,Love first,然后调用next(),那么此时它会等第二个中间件执行完毕才会继续执行第一个中间件.然后执行第二个中间件,输出我,调用next(),执行第三中间件,输出中.此时第三个中间件执行完毕,返回到第二个中间件,Export China,然后返回到第一个中间件,输出！.

// 1. 导入koa包
const Koa = require('koa')
// 2. 实例化对象
const app = new Koa()
// 3. 编写中间件
app.use((ctx, next) => {
    
    console.log('爱')
    next()
    console.log('!')
})

app.use((ctx, next) => {
    
    console.log('我')
    next()
    console.log('华')
})

app.use((ctx) => {
    
    console.log('中')
})
// 4. 监听端口, 启动服务
app.listen(3000)
console.log('server is running on http://localhost:3000')

总结

以上就是今天要讲的内容,本文仅仅简单介绍了Koa的基本使用,koaMany other powerful middlewares are also provided,Allows us to develop quickly and easily.