React JS Interview Questions & Practice Tests (600 Qs) |2026

Preparing for a React.js developer interview or want to genuinely stress-test your React knowledge? This course gives you 600 carefully written practice questions across 6 full-length tests, designed for everyone from freshers taking their first React interview to experienced developers brushing up before a senior-level role change.

You'll work through JSX, components, and props; state, events, and forms; the full React Hooks ecosystem (useState, useEffect, useContext, useMemo, useCallback, useReducer, and custom Hooks); class component lifecycle methods, error boundaries, refs, and the Context API; React Router and Redux (including Redux Toolkit); and finally performance optimization and testing with Jest and React Testing Library.

Every single question comes with a detailed explanation for each answer option, not just the correct one, so you understand exactly why an answer is right or wrong. Here's an example of what that looks like:

Question: What happens if you call a useState setter with the exact same value the state already holds?

A) React internally compares the new and old values and can bail out, skipping an unnecessary re-render as a performance optimization.
Correct — React compares the new and old values and can skip an unnecessary re-render as a performance optimization.

B) React always forces a full re-render regardless of whether the value actually changed.
Incorrect — React specifically optimizes this case rather than always re-rendering.

C) It throws a runtime error for calling the setter with an unchanged value.
Incorrect — there's nothing erroneous about this; React simply may not re-render.

D) The component unmounts and remounts.
Incorrect — this behavior is unrelated to unmounting.

This is what separates real understanding from memorization, and it's exactly the kind of reasoning interviewers probe for with follow-up questions.

Whether you're a self-taught developer, bootcamp graduate, fresher preparing for your first React role, or an experienced React developer validating your knowledge before an interview, this course is built to help you walk in with confidence. No prior React experience is required, since each explanation teaches the concept as you go.