nodejs middleware implementation

Node.js is a very powerful server-side operating environment and a popular back-end development framework. Node.js has many powerful features, one of which is middleware. Middleware is an important concept in Node.js, which provides Node.js applications with a more flexible and customizable way to handle requests. In the following article, we will discuss how to use middleware in Node.js.

What is middleware?

In Node.js, middleware is a function that can access the application request object (req), response object (res) and directly pass control to the next middleware function. Middleware functions are usually designed to perform certain operations, such as request logging, authentication, data verification, etc.

Middleware is one of the very powerful functions of Node.js. It can provide the following functions:

1. Help handle HTTP requests and responses
2. Modify requests or responses Object
3. Perform certain operations in the application
4. Skip the middleware stack
5. Install other third-party middleware

Middleware How it works

Middleware is an important feature of Node.js, and its operation mode and life cycle are very easy to understand. Simply put, when an HTTP request enters the server, all middleware functions in the application will be executed in sequence. Each middleware function can handle request and response objects, and can optionally pass the request to the next middleware.

Let us take a look at the basic usage format of middleware:

app.use(function (req, res, next) {
    console.log('This is a middleware function');
    next();
});

In the above example, we defined a middleware function. When this function is called by the application, it prints a log message and then calls the next() method. The next() method transfers control to the next middleware function (if there is one).

If the next() method is not called, the request will be suspended and will not continue. In this case, the application does not send any response. This is usually an error condition, so when writing middleware functions, be sure to call the next() method.

Classification of Node.js middleware

In Node.js, middleware can be divided into the following two types:

1. Application-level middleware
2. Route-level middleware

Application-level middleware

Application-level middleware refers to middleware that can handle all requests of the current application. This middleware is added through the app.use() method. For example, log all requests, implement authentication, and more.

let express = require('express');
let app = express();

app.use(function (req, res, next) {
   console.log('Time:', Date.now());
   next();
});

Routing-level middleware

Routing-level middleware, as the name suggests, is middleware that can only process current routing requests. This middleware is added through the use() method of the Router object. For example: implement request verification, implement caching, etc.

let express = require('express');
let router = express.Router();

router.use(function (req, res, next) {
   console.log('Request URL:', req.originalUrl);
   next();
});

Using third-party middleware

In Node.js, using third-party middleware is usually a very common practice. This approach allows us to add existing functionality to our application without having to spend time and effort writing our own code. The following is how to use a very famous third-party middleware, body-parser middleware.

let express = require('express');
let bodyParser = require('body-parser');

let app = express();

// 处理 application/x-www-form-urlencoded 类型的请求体
app.use(bodyParser.urlencoded({ extended: false }));

// 处理 application/json 类型的请求体
app.use(bodyParser.json());

Summary

In this article, we learned the definition, function and classification of Node.js middleware. Middleware is a very important concept in Node.js. Through middleware, we can add more functions and flexibility to the application. Whether it is application-level middleware or routing-level middleware, by using middleware functions correctly, you can implement your application logic in a more efficient way.

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