Real-Time Chat Application

Problem context

The client needed a real-time messaging application supporting 1,000+ concurrent users with features like typing indicators, read receipts, and file sharing. The platform had to work reliably across mobile and desktop browsers with offline support.

Implementation approach

I designed a Firestore data model with denormalized chat rooms and message sub-collections for efficient queries. Firestore's onSnapshot listeners provided real-time updates without polling. A Cloud Function handled push notifications via FCM. The UI was built with React and optimized with virtualized message lists (react-window) to handle conversations with 10,000+ messages.

Outcome and delivery impact

The application successfully handles 1,500+ concurrent users with sub-200ms message delivery. Offline support via Firestore persistence lets users compose and queue messages without connectivity. The typing indicator system uses a lightweight heartbeat mechanism that minimizes Firestore reads.

Reported metrics

• Concurrent Users
  Reported value: 1500+
• Message Delivery
  Reported value: <200ms
• Uptime
  Reported value: 99.9%
• User Rating
  Reported value: 4.8★

Technologies involved

• React
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• Firebase
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• Cloud Functions
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• FCM
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• Tailwind CSS
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