What is Express.js? An Overview in 2025

Introduction

JavaScript is one of the most popular programming languages in the world. It has been used to build websites by millions and has attracted crowds of web developers and designers.

JavaScript is one of the best programming languages to learn for those just starting out with learning to code web and mobile applications. For the first decades of its existence, JavaScript was used client-side for scripting, or to build dynamic content on the web page that performs actions based on the user’s input.

Unfortunately, this meant that developers had to code in multiple languages and web frameworks when working on the front and backend parts of the website.

The answer to this problem was Node.js. What is Node JS and how does Express relate to it? Let’s find out.

What is Node.js?

Node.js is not a programming language. It is a cross-platform runtime environment for executing JavaScript code on the server side or backend of an application or website outside of the browser.

Node.js is also not a web application framework – a platform for developing software apps. Node is built on top of JavaScript (the programming language) and helps in running frameworks (like Express).

It provides core features for server-side programming, including file system access, network communication, and event-driven programming.

With the invention of Node.js, web developers could finally use a single language for their frontend and backend development.

So, what is Express and how does it relate to Node JS?

What is Express.js?

Express.js is a popular, free, and open-source web application framework for Node.js, designed to create web apps and APIs quickly and easily.

It is based on the Node.js runtime environment and built on top of its core functionalities to provide a more streamlined and user-friendly development experience.

The Express framework is a minimalist web framework that provides a set of flexible, modular, and easy-to-use tools. This allows developers to create powerful and scalable web applications with minimal effort.

It can be used to build single-page web applications where the entire application is routed into a single index page.

Other common uses for Express are to code real-time networking applications like chat or dashboard applications, streaming apps with many asynchronous data streams, and highly-secure financial services apps like those offered by banks.

Express is also useful for creating multi-page and hybrid web applications.

Express.js provides a flexible and modular architecture, allowing developers to add or remove features as needed.

Advantages of Express.js

Consider some of the well-established advantages of using this framework to create an Express app.

Easy to Learn and Use

Express.js is easy to learn and use, making it an ideal choice for beginners. Because coding happens in JavaScript, one of the easier and most accessible programming languages to learn, it is one of the most popular frameworks for getting immersed in web development.

Its modular and flexible architecture allows developers to add or remove features as needed.

Rich Set of Middleware

Express.js provides a rich set of middleware, making it easy to handle common tasks like parsing request bodies, handling cookies, and reducing response size.

Think of middleware as software that provides common services and capabilities to apps and helps the developer build and deploy more efficiently.

It is like a bridge that connects applications, data, and users together. Middleware allows operations to be performed on HTTP requests and responses.

This means that developers can add functionality to run scripts before or after a client request, giving their program greater abilities at error handling.

This middleware functionality gives an app creator more control over the routing system to directly address client requests.

Templating Engines

Another benefit of an Express application is the use of template engines like Jade or Pug. HTML templates reduce the time-consuming process of coding by letting the developer serve static files in their app.

At runtime, the templating engine takes the static web page and replaces placeholder variables with actual values, transforms the template into HTML code, and sends it to the client’s computer.

Large Ecosystem

Express.js has a large and active community, with many plugins and modules available for extending its functionality.

Support from Google is also extensive and being open-source allows developers the opportunity to create packages and resources that extend its functionality and share them with the community at large.

Debugging

Express makes it easier to identify the exact part of an app where bugs are located. This can greatly reduce coding time when using Express to build web pages or apps.

Good Performance

Express.js is the fastest Node.js framework. This makes it a good choice for building high-performance web applications.

It also scales up well and requires little or no extra configuration when developing large-scale web and mobile applications.

Disadvantages of Express.js

Of course, nothing is perfect. As with anything, the Express framework does have a couple of disadvantages.

Lack of Structure

While Express.js provides a more structured way of organizing code compared to Node.js, it can still be difficult to maintain code as applications become larger and more complex.

Overhead

Express.js introduces some overhead compared to using Node.js directly, as it adds an additional layer of abstraction.

Example Hello World Code Snippet

Take a look at the following code as a visual example of what a simple program would look like when using Express:

Summary

Express.js is a powerful web framework that simplifies web application development. It provides a rich set of features, including access to the request-response process, middleware functionality, and a robust templating engine, making it easy to build useful and scalable web applications.

While it introduces some overhead compared to using Node.js directly, it provides a more structured way of organizing code, making it easier to build large and complex applications.

Overall, Express.js is a great choice for building web applications and APIs, and its popularity is evidence of its effectiveness and ease of use.