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Technical Interviews • 8 min

Front-End Debugging and Refactoring Interview

Learn how to approach interviews where you are asked to fix bugs, clean up code, or improve performance in an existing codebase.

What You'll Learn

  • Understand why debugging and refactoring are common in front-end interviews
  • Learn how to structure your approach when facing unfamiliar code
  • Practice strategies to make your fixes clear and well-explained

Switch to the audio version if you prefer to learn by listening rather than reading.

AI-generated audio transcript

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Why This Lesson Matters

Not every interview is about building something new. Many times, clients give you a piece of code and ask you to fix, improve, or explain it. This is realistic, outsourcing often means joining an existing codebase, not starting from scratch. Your ability to make sense of code you didn't write is just as important as your ability to create fresh components.

Don't

Assume you'll always start from an empty project

Do

  • Expect to debug existing bugs or performance issues
  • Be ready to refactor code for clarity and maintainability

The Nature of Debugging/Refactoring Interviews

Tasks are usually framed as:

  • Find and fix a bug (UI not rendering, wrong state updates, broken API integration)
  • Improve performance (e.g., avoid unnecessary re-renders, optimize loops)
  • Refactor messy code into a cleaner structure (split components, rename variables, improve state management)

Sometimes, you may also be asked to explain what the buggy code is currently doing before making changes. This checks if you truly understand it.

Don't

Rush into editing without understanding the problem

Do

  • Read the code carefully before changing anything
  • Explain your thought process out loud

What Clients Actually Evaluate

The code fix is important, but the signal they really look for is:

  • Can you understand existing code?
  • Can you explain why something is broken?
  • Can you make improvements without overcomplicating things?
  • Do you follow best practices (naming, structure, readability)?

Debugging interviews are less about writing genius solutions and more about showing that you can bring order to chaos.

How to Approach These Tasks

When faced with unfamiliar code in an interview:

  1. Scan and read: Don't type immediately, understand the structure first.
  2. Reproduce the issue: Run/test it to confirm the bug.
  3. Explain aloud: Tell the interviewer what you think is happening.
  4. Propose fixes/refactors step by step: Start small, test often, and narrate.
  5. Clean up: Leave the code better than you found it.

Don't

Try to rewrite everything from scratch during the interview

Do

  • Fix bugs in small, testable steps
  • Explain how you would refactor even if you run out of time

The Big Picture

Refactoring and debugging interviews simulate real project onboarding. Most developers will spend a large part of their job improving and fixing existing code. Showing that you can step in calmly, explain clearly, and improve what's already there is a huge hire signal.

Leave code cleaner, clearer, and more reliable than you found it, that's the real test.

Test Your Knowledge

Check how well you understood the lesson with these 1 question.

Question 1 of 1

What is usually the main goal of debugging/refactoring interviews?