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Notion·Software Engineer·Technical Phone Screen·Intermediate

IntermediatePrefer not to say
Apr 2026Remote

Summary

Notion had me build a full interactive React component from scratch during a technical screen, which was more involved than I expected for a single session. The problem was scoped well but there were a lot of moving parts to juggle at once.

Questions Asked (1)

Q1

Build a React component that takes a JSON string as input and renders a collapsible, read-only tree view with support for arbitrarily deep nesting, graceful invalid JSON handling, per-node expand/collapse state, and a working demo using a specific nested object. Also explain your component structure, state shape, and complexity tradeoffs.

Technical Trade-offsSystem DesignAPI & Integrations
Author's notes

This one ate up a lot of time.

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AI HintsAI Generated

Suggested Approach

Start by clarifying requirements and edge cases, then outline a recursive component design with local state for expansion. Walk through the implementation, explaining how you handle invalid JSON and maintain per-node state, and finally discuss tradeoffs like performance and state management.

Pro tip: Mention that you'd use a Map or Set to track expanded node paths for O(1) lookups, and consider memoization to prevent unnecessary re-renders in deep trees.

1. Clarify requirements and edge cases

Ask about expected input size, performance constraints, and whether the tree should be fully expanded by default. Confirm handling of invalid JSON and non-object values.

2. Design component structure and state

Propose a recursive TreeNode component that receives node data and a path identifier. Use a single state object (e.g., a Set of expanded paths) in the parent to control expansion.

3. Implement parsing and error handling

Use try/catch around JSON.parse to gracefully handle invalid input, rendering an error message. Ensure the component works for any JSON value, not just objects.

4. Implement recursive rendering and toggling

For each node, render a toggle button if it's an object or array, and conditionally render children based on expanded state. Use unique paths (e.g., dot-separated keys) to identify nodes.

5. Discuss tradeoffs and optimizations

Talk about time/space complexity, potential performance issues with deep trees, and optimizations like memoization, virtualization, or lazy expansion.

Key Points to Mention

  • Recursive component design with clear separation of concerns
  • State shape: using a Set or Map of expanded node paths for efficient lookups
  • Graceful error handling for invalid JSON with user-friendly message
  • Per-node expand/collapse state managed centrally to avoid prop drilling
  • Complexity: O(n) rendering time, O(d) space for recursion depth, and tradeoffs of different state management approaches
  • Demo with a specific nested object to illustrate functionality

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.