Express中间件

1.创建最基本的中间件

const express = require('express');
const send = require('send');

const app = express()

const mw = function (req, res, next) {
    console.log('middleware');

    // 一定要调用next()  把流转关系交给下一个中间件或路由
    next()
}



app.listen(80, () => {
    console.log('express server running at ');

})

2.全局生效的中间件

客户端发起的任何请求，到达服务器之后，都会触发的中间件

const express = require('express');
const send = require('send');

const app = express()

const mw = (req, res, next) => {
    console.log('middleware');

    // 一定要调用next()  把流转关系交给下一个中间件或路由
    next()
}

// 将mw注册为全局生效的中间件
app.use(mw)

app.get('/', (req, res) => {
    res.send('Home Page')
})

app.get('/user', (req, res) => {
    res.send('User Page')
})
app.listen(80, () => {
    console.log('express server running at ');

})

3.局部生效的中间件

const express = require('express');
const send = require('send');

const app = express()

const mw1 = (req, res, next) => {
    console.log('mw1');
    next()
}

// 局部生效
app.get('/', mw1, (req, res) => {
    res.send('Home Page')
})

app.get('/user', (req, res) => {
    res.send('User Page')
})
app.listen(80, () => {
    console.log('express server running at ');

})

多个局部生效的中间件

const express = require('express');
const send = require('send');

const app = express()

const mw1 = (req, res, next) => {
    console.log('mw1');
    next()
}
const mw2 = (req, res, next) => {
    console.log('mw2');
    next()
}
// 局部生效
// app.get('/', [mw1,mw2], (req, res) => {  也行
app.get('/', mw1,mw2, (req, res) => {
    res.send('Home Page')
})

app.get('/user', (req, res) => {
    res.send('User Page')
})
app.listen(80, () => {
    console.log('express server running at ');

})

4.中间件的作用

5.中间件注意事项

中间件必须在路由之前注册

6.中间件分类

应用中间件
路由中间件
错误级别中间件

错误级别中间件必须在所有路由之后

内置中间件

举例：express.json()

const express = require('express');
const send = require('send');
const app = express()

// 配置解析表单数据的中间件
app.use(express.json())

app.get('/', (req, res) => {
    console.log(req.header, req.body);

    res.send('User Page')
})
app.listen(80, () => {
    console.log('express server running at ');

})