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: ...