Openai·Frontend Engineer·Technical Phone Screen·Senior

SeniorPrefer not to say

Apr 2026Remote

Summary

Frontend Engineer interview at OpenAI that was basically one big refactoring exercise. The problem was a gnarly chat message processor full of mixed concerns and they wanted you to clean it up live while keeping a test passing.

Questions Asked (1)

You're given a messy JavaScript function that handles chat commands like /meet, /taco, and /away. It mixes parsing logic, command handling, and string manipulation all in one place. Refactor it for readability, modularity, and testability while keeping the existing test case green.

Technical Trade-offsSystem DesignAPI & Integrations

Author's notes

This is the kind of question where you can talk yourself into a corner fast.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the current behavior and test coverage, then propose a modular refactor that separates parsing, command dispatch, and formatting into pure functions. Emphasize incremental changes with tests to ensure the existing test stays green while improving readability and testability.

Pro tip: Before refactoring, add characterization tests for edge cases (e.g., unknown commands, extra spaces) to lock in behavior, then refactor in small steps—this shows you value safety over speed and understand real-world constraints.

1. Understand and characterize

Read the existing function and its test to map all inputs, outputs, and side effects. Add temporary tests for edge cases to capture current behavior.

2. Identify responsibilities

List distinct concerns: parsing the command string, dispatching to handlers, and formatting responses. Note any shared state or side effects.

3. Design modular interfaces

Define pure functions for parsing (e.g., parseCommand) and formatting (e.g., formatResponse), and a dispatcher that maps commands to handlers. Keep handlers small and focused.

4. Refactor incrementally

Extract one piece at a time, running tests after each change. Use the existing test as a safety net and add unit tests for new functions.

5. Review and iterate

Check for readability improvements, remove duplication, and ensure the public API remains unchanged. Discuss trade-offs like over-abstraction vs. clarity.

Key Points to Mention

Separation of concerns: parsing, command handling, and string manipulation should be distinct modules.
Pure functions for parsing and formatting to enable easy unit testing without mocks.
Dependency injection or a command registry to make adding new commands easy and testable.
Incremental refactoring with tests to avoid breaking existing behavior (the green test).
Trade-offs: over-engineering vs. simplicity, and when to stop refactoring.
Readability improvements: meaningful names, small functions, and clear control flow.

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