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Supio – Senior Frontend Engineer – Phone screen
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Level: Senior
Education: Masters
Years of Experience: 8
Questions Asked:
Debugging Round (Chat App)
- User sends a message but nothing happens — debug why.
- Fix missing state update on submit.
- Identify why messages aren’t persisting (missing API call, stale state).
- Why WebSocket is not reconnecting?
- Why the UI isn’t re-rendering after receiving messages (mutable state vs immutable update).
- Debug “undefined” sender ID bug in outgoing messages.
- Fix the error boundaries in Next.js app.
- Why hydration mismatch happens? (React state differ between server and client