Express.js Built-in Middleware

Express provides several built-in middleware functions that are commonly used in Express applications. These middleware functions are available out of the box and help handle tasks such as parsing request bodies, serving static files, and managing session data.

 

Key Features of Built-in Middleware

• Pre-configured: These middleware functions are pre-built and come with Express, so you don’t need to install any additional packages.
• Common Use Cases: They handle common tasks like parsing JSON data, logging requests, or serving static files.
• Can Be Combined: You can chain multiple built-in middleware functions together to handle different tasks.

 

Types of Built-in Middleware

express.json()
Parses incoming request bodies in JSON format. It is commonly used when your application expects a client to send JSON data.

Example:

app.use(express.json());

express.urlencoded()
Parses incoming requests with URL-encoded payloads (typically used with forms). It allows data to be sent as key-value pairs in the request body.

Example:

app.use(express.urlencoded({ extended: true }));

express.static()
Serves static files such as images, CSS files, and JavaScript files. It is commonly used to serve public assets like HTML files or image files.

Example:

app.use(express.static('public'));

This will allow the app to serve files from the public folder, accessible via URL paths.

express.Router()
Express Router is used to create modular, mountable route handlers. It is used for defining routes within a specific subset of your application.

Example:

const router = express.Router();

router.get('/', (req, res) => {
    res.send('Hello from router!');
});

app.use('/router', router);

express.query()
This middleware is used to parse query parameters in the URL. Express automatically parses the query string and populates req.query with the parsed object.

express.response()
This is an extension of the standard Node.js response object, with added functionality like res.json(), res.send(), res.render(), etc.

 

Example of Using Built-in Middleware

Here’s how you might use some of these built-in middleware functions in a typical Express app:

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

// Built-in middleware for parsing JSON bodies
app.use(express.json());

// Built-in middleware for parsing URL-encoded bodies
app.use(express.urlencoded({ extended: true }));

// Built-in middleware for serving static files from the 'public' directory
app.use(express.static('public'));

// Route to handle JSON data
app.post('/json', (req, res) => {
    console.log(req.body);
    res.send('JSON data received');
});

// Route to handle URL-encoded form data
app.post('/form', (req, res) => {
    console.log(req.body);
    res.send('Form data received');
});

// Starting the server
app.listen(3000, () => {
    console.log('Server running on port 3000');
});

 

Summary

Express provides several built-in middleware functions that make it easy to handle common tasks such as parsing request bodies (express.json() and express.urlencoded()), serving static files (express.static()), and creating modular route handlers (express.Router()). These middleware functions can be used to streamline your application and reduce the need for external libraries. They are easy to set up and integrate seamlessly with your routes to provide basic functionality for your application.