Detailed introduction to how to set up middleware in Node.js

In Node.js development, middleware plays a very important role, and many functions can be implemented through middleware. So, how to set up middleware? This article will give you a detailed introduction to how to set up middleware in Node.js.

1. What is middleware

Middleware can be understood as processing the request during the request and response process, and then passing the request to the next middleware or application. module. In Node.js, middleware can be seen as a series of functions. Each function handles a request and passes the request to the next middleware.

In Node.js, middleware can be mounted into the application through the app.use() method to achieve flow control of request processing.

2. Set up middleware

In Node.js, common middleware include logging, request processing, permission verification, error handling, etc. The method of setting middleware is as follows:

1. Installing middleware

Node.js provides a lot of middleware, which can be installed through the npm command:

$ npm install <middleware-name>

2. Introducing middleware

In Node.js, you can use the require() function to introduce middleware:

const express = require('express');
const logger = require('morgan');
const app = express();

In the above code, we introduced express and morgan two middlewares and created an application instance app using express().

3. Use middleware

In Node.js, use middleware through the app.use() method, the syntax is as follows:

app.use([path], function(req, res, next) {
    // 中间件处理逻辑
    next();
});

Among them, path is an optional parameter that can limit the request path processed by the middleware. If the path parameter is omitted, the middleware will handle all requests.

Taking the above code as an example, let's take a look at how to use morgan middleware:

app.use(logger('dev'));

The above code will use morgan middleware to record logs. Among them, 'dev' means using colored and formatted output logs.

4. Execution of middleware

In Node.js, the execution order of middleware is executed in the order set. Each middleware can pass the request to the next middleware or respond directly to the request.

app.use(function(req, res, next) {
    console.log('我是第一个中间件');
    next();
});

app.use(function(req, res, next) {
    console.log('我是第二个中间件');
    res.send('hello');
});

app.listen(3000);

In the above code, we first output a message and then pass the request to the next middleware. The second middleware outputs another message and then returns the "hello" string to the client.

Summary:

This article briefly introduces how to set up middleware in Node.js. I hope it will help you understand the importance of middleware and how to use middleware.

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