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Salesforce·Software Engineer·Technical Phone Screen·Intermediate

IntermediatePrefer not to say
May 2026Remote

Summary

Frontend coding round at Salesforce, one question the whole time: build a traffic light component in React. Seemed straightforward until they started asking about cleanup and accessibility.

Questions Asked (1)

Q1

Build a Traffic Light component that cycles through Red, Green, and Yellow states with configurable durations for each state. Handle timer cleanup, expose start/stop/reset controls, and discuss accessibility considerations.

Technical Trade-offsSystem Design
Author's notes

I got the basic render and cycling logic down pretty quick, but the timer cleanup part is where I started fumbling.

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AI HintsAI Generated

Suggested Approach

Start by clarifying requirements and edge cases, then outline the component's state machine and timer management. Implement the component with a focus on clean lifecycle handling and accessibility, and finally discuss trade-offs and potential improvements.

Pro tip: Demonstrate awareness of real-world usage by mentioning how you would handle rapid start/stop toggles and ensure no memory leaks, and proactively bring up testing strategies for timers.

1. Clarify Requirements and Edge Cases

Ask questions to confirm expected behavior: default durations, whether durations are configurable at runtime, and how the component should behave on unmount. Consider edge cases like zero durations or rapid toggling.

2. Design the State Machine and Timer Logic

Define the states (Red, Green, Yellow) and transitions. Decide on using setTimeout or setInterval, and plan how to store the timer ID for cleanup. Ensure that changing durations or stopping/starting resets the timer appropriately.

3. Implement the Component with Controls

Write the component code, exposing start, stop, and reset methods. Use lifecycle methods (or hooks) to clean up timers on unmount. Ensure that the UI reflects the current state and that controls are accessible.

4. Address Accessibility

Add ARIA attributes such as role='status' or aria-live to announce state changes. Ensure color is not the only indicator (e.g., add text labels). Make controls keyboard accessible and provide sufficient contrast.

5. Discuss Trade-offs and Testing

Talk about trade-offs between setTimeout and setInterval, and between internal vs external state management. Mention how you would test the component, including mocking timers and testing accessibility.

Key Points to Mention

  • Use of setTimeout for each state transition to avoid drift and allow dynamic duration changes.
  • Proper cleanup of timers in componentWillUnmount (or useEffect cleanup) to prevent memory leaks.
  • Exposing imperative controls (start/stop/reset) via refs or callbacks, and ensuring they are idempotent.
  • Accessibility: ARIA live regions, role='status', text labels, and keyboard-navigable controls.
  • Handling edge cases: zero durations, rapid start/stop, and unmount during a timer.
  • Testing strategy: using Jest fake timers and React Testing Library to verify state transitions and cleanup.

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