How to Build Middleware in Node.js?

Middleware in Node js is a function that plays a vital role in the request-response lifecycle of Node js execution. In the context of web development, middleware is a term used to describe software elements that reside between multiple application components and manage activities including request processing, authentication, logging, and error handling. Middleware connects the client’s request and the server’s response, to put it another way.

Before handing off control to the following middleware in the chain, middleware functions can conduct operations on or alter the request and response objects since they have access to them and are successively operated. This sequential execution enables programmers to separate an application’s complex logic into manageable chunks.

Middleware in Node Js

The Node.js web frameworks Express.js, Koa.js, and Hapi.js regularly use middleware. These frameworks provide a dependable way to manage middleware and incorporate it into the application’s architecture.

A function that has access to request objects, response objects, and subsequent middleware functions is all that middleware is. It is present between the Node.JS execution cycles for requests and responses. The variable ‘req’ usually refers to the request object, whereas the variable ‘res’ usually refers to the response object. It should be noted that middleware can handle ‘req’ objects before the server sends a response.

There are many things we can do with Node.JS middleware. With middleware functions, we can run any code at first. Additionally, we can modify the response and request objects. The request and response cycle can be stopped during Node.JS operation. The following middleware function in the queue for Node.JS execution can also be called.

Middleware Stack

Middleware operations are arranged in a stack in Express.js, and they are carried out in the order they are added to the stack. You can adequately manage the flow of requests and responses due to this sequential execution. Middleware can be installed locally, which only affects particular routes or route groups, or globally, which affects all routes.

Types of Middleware in Node js

In Node.js, middleware comes in a variety of forms, each with an individual or specific purpose. Here are a few examples

  • Logger Middleware: Logs incoming requests, useful for debugging and monitoring.
  • Authentication Middleware: Verifies user’s identity and grants or denies access accordingly to protect routes.
  • Error Handling Middleware: Used for error handling that occurs during request processing.
  • Body Parsing Middleware: Used to parse incoming request bodies like JSON data or any other form of data and make it accessible in the request object.
  • Session Middleware: Used to handle or manage users’ sessions and state across requests.
  • CORS Middleware: Manage Cross-Origin Resource Sharing to allow or deny requests from different platforms.
  • Compression Middleware: Helps in compressing response data to reduce bandwidth usage and improve performance. 
  • Security Middleware: Helps implement security measures such as input validation, CSRF(Cross-Site Request Forgery) protection, and XSS prevention.
  • Custom Middleware: Developers can create custom middleware to address specific application requirements.

In the context of Node.js, it is essential to acknowledge the presence of various middleware components. To illustrate this concept more clearly, we can focus on two middleware modules: Multer and Body Parser.

Using Multer as a Middleware in Node js to upload file

Multer is a middleware that was created specifically to handle multipart/form data, which is frequently used for file uploads. The middleware Multer was created primarily to handle multipart/form data, which is frequently used for file uploads. 

In Node.js applications, Multer is a well-liked middleware for managing file uploads. Receiving and storing client-uploaded files is made easier by it. Here’s a little example of how to utilize Multer in an Express.js application to manage file uploads. 

const express = require('express'); const multer = require('multer'); const app = express(); // Configure Multer const storage = multer.diskStorage({ destination: (req, file, cb) => { cb(null, 'uploads/'); }, filename: (req, file, cb) => { cb(null, + '-' + file.originalname); }, }); const upload = multer({ storage }); // Route for file upload'/upload', upload.single('file'), (req, res) => { res.send('File uploaded successfully'); }); app.listen(3000, () => { console.log('Server is running on port 3000'); });
Code language: JavaScript (javascript)

Using body-parser as a Middleware in Node js to parse data

The node js middleware component body-parser is crucial for parsing request bodies, especially when working with POST and PUT requests. Previously, Express.js included body-parser; however, as of version 4.16.0, it must now be installed independently via npm.

To use body-parser, we can add it as application-level middleware like this

const express = require('express'); const bodyParser = require('body-parser'); const app = express(); // Parse JSON and URL-encoded request bodies app.use(bodyParser.json()); app.use(bodyParser.urlencoded({ extended: true })); // Route to handle POST requests with JSON data'/api/data', (req, res) => { const data = req.body; res.json(data); }); app.listen(3000, () => { console.log('Server is running on port 3000'); });
Code language: PHP (php)

The node js body-parser middleware for JSON and URL-encoded request bodies are added in this example using app.use. The request body is parsed by this middleware and made accessible to route handlers as req.body.

NPM Body Parser

To make the process of parsing incoming HTTP request data in Node.js applications easier, the npm Body Parser is a well-liked middleware package. It is essential for managing data that clients, such as web browsers or mobile apps, send to the server. By providing developers with a simple method to extract data from HTTP requests, Body Parser significantly reduces the difficulty of processing raw data. This opens developers up to focus more on developing the core functionality of their apps.

When making an HTTP request to a Node.js server, a client frequently sends data in several formats, such as JSON, URL-encoded data, or multipart data for file uploads. This data can be challenging and error-prone to manually parse. Here npm Body Parser comes into action.


Adding functionality to the request-response cycle is made possible by middleware, a basic idea of Node.js applications. Building robust and feature-rich Node.js apps requires an understanding of how to utilize and build middleware and use of body parser in node js, whether you’re managing file uploads with Multer, parsing request bodies with body-parser, or building custom middleware. You may improve the security, speed, and functionality of your Node.js projects by taking advantage of middleware’s capabilities.

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