How to use the React MCQ Quiz
- 1. Choose the length10 random React questions, or all 25.
- 2. AnswerTap an option. You see straight away whether it's right, with a one-line reason.
- 3. ReviewFinish to get your score and a list of every question with the correct answer.
What's covered
- Basics: JSX, fragments, className and why component names start with a capital.
- Props and state: read-only props, useState, not mutating state, and why two
setCount(count + 1)calls add only 1. - Lists: what keys do and why index keys cause bugs.
- Hooks: useEffect timing and cleanup, the rules of hooks, useRef, useMemo and useCallback.
- State management and forms: Context, controlled inputs and preventDefault.
- Rendering: the virtual DOM, when components re-render, React.memo and conditional rendering traps.
- Routing and data: React Router v6 Route and useNavigate, and where to fetch data.
A sample question explained
After setCount(count + 1) runs twice in one click handler, how much does count go up? By 1. Both calls read the same count from the current render, so both ask React to set the same next value. The fix is the updater form, setCount(c => c + 1), which receives the latest pending value each time, so two calls add 2.
Another common trap: {count && <Badge />} shows a stray 0 on the page when count is 0, because React renders the number 0. Use {count > 0 && <Badge />}. Questions like these appear often in front-end interviews because they show whether you understand how React renders, not just the syntax. Retakes shuffle the questions.
Frequently asked questions
Does the quiz cover class components?
No. It focuses on function components and hooks, which are the current standard.
Which React version?
React 18 and 19 behaviour, including Strict Mode running effects twice in development.
Who wrote the questions?
Uncodemy, to cover common front-end interview topics. They aren't from any company's test.
Is the React MCQ quiz free to take?
Yes. The React MCQ quiz lets you answer every question with no form. At your first score screen we ask for your name and WhatsApp number once; after that, the React MCQ quiz and all other Uncodemy tools stay open.