Building Real-time Communication with Socket.io

Modern apps—from chat tools and multiplayer games to live dashboards and collaborative editors—rely on real-time communication. Traditional HTTP request-response cycles don’t cut it when you need instant updates.

That’s where WebSockets and libraries like Socket.io come into play. Socket.io provides a high-level abstraction over WebSockets (and falls back to other transports when necessary), making the use of real-time features in an Express app easy.

In this lesson, we’ll explore how to add real-time chat functionality to an Express application using Socket.io.

Understanding real-time communication

Real-time communication refers to the instantaneous data exchange between client and server without requiring the client to refresh or make new HTTP requests.

Unlike traditional request-response cycles, where users must manually refresh to see updates, real-time systems push updates as they occur. This approach powers chat applications like Slack and WhatsApp and collaborative tools such as Google Docs and Figma.

Under the hood, real-time data flow is commonly powered by WebSockets, a protocol that opens a persistent, bidirectional connection between the browser and server.

What is Socket.io?

Socket.io is a JavaScript library that simplifies WebSocket communication by adding powerful features like:

• Automatic reconnections

• Event-based messaging

• Room and namespace support

• Fallbacks for older clients (e.g., long polling)

Socket.io consists of two parts:

• A server-side library for Node.js

• A client-side library that runs in the browser

Together, they let an app send and receive messages in real time with minimal boilerplate, while maintaining compatibility across various environments and browsers.

Setting up Socket.io in an Express app

Previously, we set up our Express server like this: