app.js

const express = require('express')

// 本次 http 请求实例
const app = express()

app.use((req, res, next) => {
  console.log('请求开始...', req.method, req.url)
  next()
})

app.use((req, res, next) => {
  // 假设在处理 cookie
  req.cookie = {
    userId: 'abc123',
  }
  next()
})

app.use((req, res, next) => {
  // 假设处理 post data
  // 异步
  setTimeout(() => {
    req.body = {
      a: 100,
      b: 200,
    }
    next()
  })
})

app.use('/api', (req, res, next) => {
  console.log('处理 /api 路由')
  next()
})

app.get('/api', (req, res, next) => {
  console.log('get /api 路由')
  next()
})

app.post('/api', (req, res, next) => {
  console.log('post /api 路由')
  next()
})

// 模拟登陆验证
function loginCheck(req, res, next) {
  // setTimeout(() => {
  //     console.log("模拟登陆成功");
  //     next();
  // });
  setTimeout(() => {
    console.log('登陆失败')
    res.json({
      error: -1,
      msg: '登陆失败',
    })
  })
}

app.get('/api/get-cookie', loginCheck, (req, res, next) => {
  console.log('get /api/get-cookie')
  res.json({
    error: 0,
    data: req.cookie,
  })
})

app.post('/api/get-post-data', (req, res, next) => {
  console.log('post /api/get-post-data')
  res.json({
    error: 0,
    data: req.body,
  })
})

app.use((req, res, next) => {
  console.log('处理 404')
  res.json({
    error: -1,
    msg: '404 not fount',
  })
})

app.listen(3000, () => {
  console.log('server is running no port 3000')
})

package.json

{
  "name": "express-test",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "keywords": [],
  "author": "",
  "license": "ISC",
  "dependencies": {
    "express": "^4.17.1"
  }
}