Koa2中间件的作用及路由实现实例详解

// 中间件，暴露一个函数
module.exports = function () {
  return async function (ctx, next) {
    pv(ctx);
    // 执行下一个中间件，没有下一个中间件就执行完了
    await next();
  };
};

const koa = require('koa')
const app = new koa()
app.use(async (ctx,next) => {
    console.log('1')
    await next()
    console.log('1-1')
    ctx.body = 'hello world'
})
app.use(async (ctx,next) => {
    console.log('2')
    await next()
    console.log('2-1')
})
app.use((ctx) => {
    console.log('3')
})
app.listen(3000)

const koa = require('koa')
const app = new koa()
app.use(async (ctx) => {
    if (ctx.url === '/') {
        console.log('这是首页');
        ctx.body = '这是首页'
    } else if (ctx.url === '/user') {
        if (ctx.method === 'GET') {
            console.log('这是用户列表页');
            ctx.body = '这是用户列表页'
        } else if (ctx.method === 'POST') {
            console.log('添加用户');
            ctx.body = '添加用户'
        }
    } else {
        ctx.status = 404
    }
})
app.listen(3000)

const koa = require('koa')
const Router = require('koa-router')
const app = new koa()
const router = Router({
    prefix: '/user'
})
router.get('/', async (ctx) => {
    ctx.body = '这是用户首页'
})
router.get('/del', async (ctx) => {
    ctx.body = '删除用户'
})
router.post('/add', async (ctx) => {
    ctx.body = '添加用户'
})
app.use(router.routes())
app.listen(3000)