Scale AI·Software Engineer·Technical Phone Screen·Intermediate

IntermediatePrefer not to say

May 2026Remote

Summary

Scale AI SWE coding round. You get a partially built React app and have to finish it. More UI wiring than algorithm work, which honestly threw me off a bit since I came in expecting leetcode.

Questions Asked (2)

Build a custom React hook that fetches data from a provided API using useEffect with an async function, then transforms the response into a specified format. The hook should expose loading and error states alongside the converted data.

API & IntegrationsTechnical Trade-offs

Author's notes

The async-inside-useEffect pattern tripped me up for a second.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the requirements: the hook should accept a URL and a transform function, manage loading and error states, and return the transformed data. Then, outline the hook's structure using useState for state management and useEffect for fetching, ensuring proper cleanup to avoid memory leaks. Finally, discuss potential optimizations like caching or aborting requests, and how to handle edge cases such as unmounting during fetch.

Pro tip: Demonstrate awareness of race conditions by using an AbortController or a cancellation flag in the effect cleanup, and mention that you'd extract the fetch logic into a separate async function to keep the effect callback clean.

1. Clarify Requirements and API

Ask clarifying questions about the hook's parameters (e.g., URL, transform function, dependencies) and the expected return shape (data, loading, error). Confirm whether the hook should refetch on URL change or other triggers.

2. Design the Hook's State and Effect

Use useState to manage data, loading, and error states. In useEffect, define an async function that fetches data, applies the transform, and updates state, handling errors appropriately.

3. Implement Cleanup and Cancellation

Return a cleanup function from useEffect that cancels the fetch (e.g., via AbortController) or sets a flag to ignore stale responses, preventing state updates after unmount or on rapid dependency changes.

4. Optimize and Handle Edge Cases

Consider memoizing the transform function or using useCallback to avoid unnecessary refetches. Discuss handling empty responses, network errors, and loading states during refetch.

5. Test and Validate

Mention writing unit tests with React Testing Library and mocking fetch to verify loading, success, and error states, as well as cleanup behavior.

Key Points to Mention

Using useState for data, loading, and error states
Using useEffect with an async function defined inside and called immediately
Implementing cleanup with AbortController or a cancellation flag to avoid memory leaks
Handling errors with try/catch and updating error state
Applying the transform function to the fetched data before setting state
Considering dependencies array to control when the effect runs (e.g., URL, transform)

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

Modify an existing UI component to support opening and closing a modal, expanding and collapsing a list, and wiring up several buttons to perform specified actions. All interactions need to be connected to component state and the custom hook.

API & IntegrationsTechnical Trade-offs

Author's notes

This felt like a lot of small things at once.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the component's current structure and the custom hook's role, then outline a plan to lift state into the hook and pass down handlers. Implement each interaction (modal, list, buttons) incrementally, ensuring state updates are predictable and testable. Finally, discuss trade-offs like controlled vs uncontrolled components and performance optimizations.

Pro tip: Emphasize that you would first write or update tests for each interaction before refactoring, ensuring the component's behavior remains correct. This demonstrates a test-driven approach and reduces regression risks.

1. Clarify Requirements and Current State

Ask questions to understand the existing component, the custom hook's API, and any constraints. Review the code to identify where state currently lives and how interactions are handled.

2. Design State Management

Decide which state should live in the custom hook (e.g., modal open, list expanded) and which should remain local. Plan how to expose state and updater functions from the hook.

3. Implement Interactions Incrementally

Modify the component to use the hook's state and handlers for the modal, list, and buttons. Test each interaction in isolation before moving to the next.

4. Ensure Reusability and Performance

Check that the hook is reusable across similar components and optimize re-renders (e.g., useCallback, useMemo) where necessary. Discuss trade-offs of different approaches.

5. Validate with Tests and Edge Cases

Write or update unit and integration tests to cover opening/closing, expanding/collapsing, and button actions. Consider edge cases like rapid toggling or disabled states.

Key Points to Mention

Separation of concerns: keeping UI logic in the component and state logic in the custom hook.
Controlled vs uncontrolled components and when to use each for modals and lists.
Performance optimizations: memoization, avoiding unnecessary re-renders, and using React.memo.
Accessibility considerations: focus management, ARIA attributes for modal and expandable list.
Testing strategy: unit tests for the hook, integration tests for the component interactions.
Trade-offs: lifting state vs prop drilling, and the impact on component reusability.

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