React Interview Questions

This is the most common real task a junior React dev will do on day one. It reveals whether they understand useEffect, state management, and cleanup, or just memorized a tutorial.

Infinite render loops are one of the most common bugs juniors create. This question shows whether they actually understand dependency arrays or just add things until the warning goes away.

Tests basic event handling and immutable state updates. Candidates who mutate arrays directly or use index as both key and ID will introduce subtle bugs in production lists.

Form handling is 80% of frontend work. This separates developers who understand React's data flow from those who fight the framework every time they build a form.

Reveals whether the candidate knows when to reach for Context instead of prop drilling. A junior who can set up a provider/consumer pattern will ramp up faster on any real codebase.

Shows how the candidate actually works day to day. Developers who invest in their tooling (DevTools, linters, AI assistants) ship faster and catch bugs earlier than those who code in a bare editor.

Most juniors have never needed useLayoutEffect. If they know the difference, it signals they've hit real visual bugs (flickering, measurement issues) and dug into how the browser paint cycle works.