How would you build a poll/voting system with real-time results in React?

🧩 Scenario

You want to build a live poll widget like YouTube Live or Slido:

• Users vote instantly
• Results update in real-time as others vote
• Support optimistic voting
• Prevent duplicate votes
• Show animations during result changes
• Persist results on server

🧠 Answer (Design Overview)

Architecture

1. Initial Load

   • Fetch poll + current vote counts via REST.

2. Real-time Updates
   Use WebSockets or SSE to broadcast changes:

   {
     type: 'vote:update', optionId, total;
   }
   

3. Optimistic Voting Flow

   • Immediately update UI as if vote succeeded
   • Send vote to server
   • On failure → rollback + show error

4. De-duplication / Validation

   • Store user vote on server
   • Prevent multiple votes per poll (unless multi-vote allowed)

5. Result Calculation

   • Use percentage-based UI:

   pct = (option.votes / totalVotes) * 100;
   

6. Smooth UI Animations

   • Use CSS transitions for bar width updates
   • Use counters that animate from previous to new values

Tradeoffs:

• WebSockets give instant bi-directional updates but require more infra.
• SSE is simpler for one-way streams.

🎮 Live Demo: Real-time Poll/Voting System

🔍 Real-World Tips

• Use Redis Pub/Sub or Socket.io rooms to broadcast updates.
• Use Kafka or event streams for massive-scale voting.
• For mobile users, debounce rapid taps.
• Prevent UI flash by using smooth width transitions.

Quick Practice

1. Add result ordering (most voted first).
2. Add pie chart rendering.
3. Add anonymous vs authenticated voting modes.
4. Add end-of-poll countdown timer.

Summary

• Real-time polls combine optimistic UI, WebSockets, and dynamic animations.
• Always validate and de-duplicate votes on the server.
• Broadcast vote updates to keep all clients in sync.