Real-time Chat App

Overview

Create a multi-room chat application. Users log in, join rooms, send messages that appear instantly for all participants, see who is typing, and view online/offline status. Messages persist in MongoDB with pagination for history loading.

Real-time chat is one of the most challenging full-stack projects because it exercises every layer of the stack simultaneously. The frontend must handle optimistic message rendering, scroll position management during history loading, and real-time updates from multiple rooms. The backend must manage persistent WebSocket connections, room-based broadcasting, user presence tracking, and message persistence.

Socket.io abstracts much of the WebSocket complexity but you still need to design the event protocol, handle reconnection gracefully, prevent duplicate messages, and maintain correct message ordering when network conditions are poor. These are the same challenges that Slack, Discord, and Microsoft Teams solve at scale.

For interviews, this project demonstrates WebSocket expertise, real-time state synchronization, and the ability to handle distributed system challenges like reconnection, eventual consistency, and offline queuing. These skills are highly relevant for any role involving real-time features.

Interview questions

• How does Socket.io room management work?
• How do I implement typing indicators?
• How should I paginate message history?
• How do I handle reconnection?
• How do I prevent duplicate messages?
• How do I implement online presence tracking?

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