React Practice Test: 120 Questions with Explanations

If you are preparing for a React skills assessment — a freelance-platform skills test, an agency badge, or a technical screen — this is a full practice bank covering everything those tests draw from.

A note on what this is. These are original practice questions, not a copy of any actual exam. Real test questions are confidential, and sites that publish them get taken down. What is here is more useful anyway: every question includes an explanation of why the answer is right, which is what actually gets you through an assessment you cannot memorise your way past.

How the tests actually work

Skills assessments on freelance platforms pull from standard React knowledge — the same material a technical interviewer would cover. In practice that means:

• Multiple choice, timed. Usually 30–40 questions in 15–20 minutes, so roughly 30 seconds each. You do not have time to reason from first principles on every question.
• Heavily weighted toward hooks. Rules of Hooks, dependency arrays, and the useState/useRef distinction come up constantly.
• Trick questions about closures and batching. The setCount(count + 1) three times question, or some variant, appears on nearly every React assessment.
• A few questions on whatever shipped recently. Right now that means React 19 — Actions, the use API, and ref-as-prop.

You typically cannot retake immediately, so the cost of walking in cold is a locked category for weeks.

What is covered

120 questions across 21 topics, every answer explained.

Difficulty splits roughly 23% beginner, 46% intermediate and 31% advanced.

The eight that trip people up

If you are short on time, make sure you can answer these cold. Each one appears in some form on nearly every React assessment.

1. 1{0 && <Component />} renders 0, not nothing.The && operator returns its left operand when falsy, and React renders 0 as text. Use count > 0 && instead.
2. 2Calling setCount(count + 1) three times increments by one.State is constant within a render, so all three calls compute the same value. The updater form setCount(c => c + 1) is what gives you three.
3. 3useEffect running twice in development is StrictMode, not a bug.It simulates unmount and remount to expose missing cleanup. It does not happen in production.
4. 4Index keys break when lists reorder.The symptom is component state — input values, checkboxes — attaching to the wrong row.
5. 5useRef updates do not re-render; useState updates do.That single difference determines which one you reach for.
6. 6React.memo fails when props are new references.An inline arrow function or object literal is a new reference every render, so the shallow comparison always reports a change.
7. 7Changing a key resets all of that component's state.This is occasionally the fix you want, not a bug.
8. 8Error boundaries do not catch event handler errors.They only catch errors thrown during rendering of descendants.

How to use this bank

Work through it in study mode first — answer, read the explanation, move on. Do not grade yourself yet. The explanations are the actual content; the questions are just the delivery mechanism.

Then do a timed runat 30 seconds per question on a filtered subset. That is the real test condition, and it exposes the difference between “I understand this” and “I can recall this under time pressure.”

Anything you miss twice, go read the React docs section for it rather than re-reading the explanation. The explanation tells you the answer; the docs tell you the model that generates the answer.