What is Express?

Last Updated : 23 Jul, 2025

Express is a minimal and flexible web application framework for NodeJS. It provides a robust set of features for building dynamic web applications and APIs, making it one of the most popular frameworks used in the development of web applications on the server side.

Simplifies routing and middleware management.
Supports various template engines for dynamic content.
Provides rapid development with a robust set of features.

What-is-express-js-copy — What is Express?

Prerequisites: JavaScript, NodeJS

Why Use Express?

Minimal and Flexible: Express is unopinionated, which means it does not force developers to follow a particular structure or design pattern. It offers just the essentials and allows developers to decide how to structure their application.
Speed: Express is highly efficient due to its minimalistic nature. This makes it a great choice for applications that need high-performance and low overhead.
Middleware: Express has a built-in middleware framework that allows you to add various functions such as authentication, logging, and error handling to your application without cluttering the core business logic.
Routing: Express provides a powerful routing system that is flexible and easy to use for defining HTTP routes for handling requests like GET, POST, PUT, DELETE, etc.
Template Engine Support: Express supports various template engines like EJS, Pug, and Handlebars, making it easier to build dynamic HTML pages.

Features of ExpressJS

1. Routing

Defines how an application's endpoints respond to client requests.
Simplifies handling of different HTTP methods (GET, POST, etc.) at various URL paths.
Enables creation of clean and maintainable URL structures.

2. Middleware

Functions that execute during the request-response cycle.
Facilitates tasks like logging, authentication, and parsing request bodies.
Allows modular addition of functionalities to applications.

3. Error Handling

Provides mechanisms to manage application errors gracefully.
Supports both synchronous and asynchronous error handling.
Enables centralized error management for consistent responses.

4. Request & Response Objects

Enhances NodeJS's req and res objects with additional methods.
Simplifies tasks like redirecting, rendering, and sending responses.
Provides utilities for handling query parameters and form data.

5. Body Parsing

Parses incoming request bodies in various formats (e.g., JSON, URL-encoded).
Simplifies access to data sent by clients in POST requests.
Eliminates the need for manual parsing of incoming data.

How Does Express Work?

Request-Response Cycle: When a client (e.g., a browser) sends a request to a server, Express processes the request based on the route and method specified. The application processes the request through various middleware functions and eventually sends back an HTTP response.
Middleware Flow: Middleware functions are executed in the order they are defined in the code. They handle incoming requests, perform operations on the request object (such as validating data or modifying headers), and pass control to the next middleware or route handler.
Routing: Express matches the incoming request to the appropriate route based on the URL path and HTTP method (GET, POST, etc.). Once a match is found, Express executes the associated route handler.
Rendering Views: Express supports rendering views using template engines, which can dynamically generate HTML based on data passed from the route handlers.

Use Express in your Node Application

Step 1: In the existing Node Application install Express.

npm install express

The updated dependencies in package.json file will look like:

"dependencies": {
    "react": "^18",
    "react-dom": "^18",
    "express": "^4.17.3",
  },

Step 2: In the app.js file add the following code.

JavaScript

//app.js

const express = require('express');
const app = express();
const PORT = 4000;

// Define a basic route
app.get('/', (req, res) =&gt; {
    res.send('Welcome To GeeksforGeeks!');
});

// Start the server
app.listen(port, () =&gt; {
    console.log(`Server is running on http://localhost:${PORT}`);
});

Step 3: To start the application run the following command.

node app.js

Output

Advantages of Express

Simplifies web server development on NodeJS.
Offers a minimalist and flexible framework for scalability.
Enhances code readability and maintainability.
Accelerates development with a feature-rich API.
Facilitates a vibrant ecosystem for easy integrations.

Disadvantages of Express

Limited support for real-time applications out of the box.
Asynchronous code can lead to callback hell (callback-based nested code).
Relatively steeper learning curve for beginners compared to simpler frameworks.
Express itself is unopinionated, which may require additional decision-making on project structure.
Less built-in functionality compared to larger frameworks like Django or Ruby on Rails.

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