Middleware of express framework in nodejs and analysis of app.use and app.get methods

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Use node to develop projects. Express is a commonly used framework. The following introduces the core usage middleware and the use and get methods of the app:

The implementation of middleware is very simple:

// 一个简单的中间件
function middleware(req, res, next){
    // req 参数可以接受一些请求的参数(req.query/req.body) 和 请求头信息
    // res 用于响应信息
    // 调用next()方法则进入下一个中间件
}

// 几种常见的调用方式
app.use(middleware);
app.use('/user',middleware); // 匹配部分路径
app.get('/login',middleware);

Next are some uses of app.get/use:

app.get(path,function); // 接收两个参数 路径 和 一个回调函数
app.use(path,function/router); // 也是接收两个参数 路径和get的区别是第二个可以放回调函数或者router对象

//值得注意的是，path如果忽略，如:app.use(function/router);也是合法的写法，表示匹配所有的路径

Regarding the writing of path and function, the following example:

// get 访问示例会匹配/app和其子集路径，如:http:127.0.0.1:3000/app 以及http:127.0.0.1:3000/app[/aa/bb...等等]都会匹配
app.get('/app',(req, res, next) => {
    //TODO SOMETHING...
});

//use 路由匹配和get方法一样
app.use('/app',(req, res, next) => {
    //TODO SOMETHING...
});

//另一种写法
app.use((req, res, next) => {
    //TODO SOMETHING...
});

But we often see this kind of Writing method:

const session = require('express-session');

app.use(session({
    secret: 'test01',
    resave: false,
    saveUninitialized: false
}));

In fact, the implementation behind it is also very simple. Just return a class (req, res, next) => {} function, for example:

// 实现思路
app.use(myFunction());

function myFunction(){
// 做一些处理
    return (req, res, next) => {
        next();
    }

}

Related recommendations:

Example to explain the method of obtaining get and post values ​​​​and session verification in express in nodejs

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