React Developer track
React interview questions and answers
React interviews check that you know why components render, how hooks and effects work, and how to keep state simple. Then you write or fix a component. Practice both with follow-ups that dig into the why.
Questions
Interview questions and answers.
Real questions from this track, from easier to harder, with what a good answer covers. In the mock interview, each one comes with follow-ups based on what you say.
What is a component in React?
A good answer covers that a component is a function that returns what should be on screen.
What is the difference between props and state?
A good answer covers that props come from the parent and the component should not change them.
How does useState work?
A good answer covers that useState returns the current value and a function to set it.
Why do items in a list need a key?
A good answer covers that keys tell React which item is which from one render to the next.
What is useEffect for?
A good answer covers that useEffect runs code after render to keep in step with something outside React.
What is a controlled input?
A good answer covers that a controlled input takes its value from state and reports changes with onChange.
What is JSX?
A good answer covers that JSX is syntax that compiles to function calls that create elements.
How do you handle a click in React?
A good answer covers that you pass a function, like onClick={handleClick}, not a call to it.
How do you show or hide part of a component?
A good answer covers that you choose what to return with if, a ternary or &&.
How do you reuse UI between React components?
A good answer covers that you build small components and combine them.
How do you fetch data in a React component?
A good answer covers that fetching in an effect needs loading, error and cleanup handling.
When does a React component re-render?
A good answer covers that it re-renders when its state changes or its parent re-renders.
How do you decide what goes in an effect's dependency list?
A good answer covers that every value from the component used inside the effect belongs in the list.
What is useRef for?
A good answer covers that a ref holds a value that survives renders without causing one.
Two sibling components need the same data. What do you do?
A good answer covers that the state moves up to their closest shared parent.
When should you use context in React?
A good answer covers that context passes a value deep into the tree without props at every level.
What is a custom hook, and when do you write one?
A good answer covers that a custom hook is a function starting with use that calls other hooks.
What is derived state, and why avoid storing it?
A good answer covers that a derived value, like a filtered list, can be computed during render.
How would you build a form with validation in React?
A good answer covers that field values live in state or in a form library's store.
What does Strict Mode do in development?
A good answer covers that it renders components and runs effects twice in development.
When do React.memo, useMemo and useCallback actually help?
A good answer covers that memo skips re-rendering a child when its props are the same.
What do useTransition and useDeferredValue do?
A good answer covers that they mark some updates as less urgent so typing stays responsive.
When would you add a state library like Redux or Zustand?
A good answer covers that local state and context cover most apps.
How do you test a React component?
A good answer covers that you render it and act the way a user would, with Testing Library.
How does React decide what to change in the DOM?
A good answer covers that React compares the new element tree with the previous one.
What is batching in React 18 and later?
A good answer covers that several state updates in one event are applied in a single re-render.
What is Suspense for?
A good answer covers that Suspense shows a fallback while something inside it is still loading.
How do you handle a component that throws while rendering?
A good answer covers that an error boundary catches errors while rendering below it and shows a fallback.
What is a stale closure in React hooks?
A good answer covers that each render's functions see that render's props and state.
What are React Server Components?
A good answer covers that server components run only on the server and send no JavaScript for themselves.
What goes wrong during hydration, and how do you avoid it?
A good answer covers that the HTML sent by the server must match the browser's first render.
How would you structure a large React codebase for several teams?
A good answer covers that code is grouped by feature, not by file type.
A React page feels slow while the user types. How do you find and fix the cause?
A good answer covers that the React Profiler shows which components render and why.
How do server actions and form actions change form handling?
A good answer covers that a form can call a server function directly, without a hand-written API route.
What does the React Compiler change about memoization?
A good answer covers that it memoizes components and values automatically at build time.
How would you design data loading in a large React app so pages do not load in a chain of waits?
A good answer covers that a route's data requests start together, at the route level or on the server.
How would you choose between a single-page app, server rendering, static pages and server components for a new product?
A good answer covers that each page's needs for freshness, search and interactivity decide how it renders.
How would you upgrade a large app across a major React version?
A good answer covers that you read the breaking changes and fix deprecated APIs first, in small steps.
How would you model state for a complex editor with several steps and undo?
A good answer covers that a reducer with clear actions keeps updates predictable.
How would you build an accessible component library in React?
A good answer covers that headless parts hold behavior and accessibility while styles stay swappable.
What it covers
Topics.
How it works
How the mock interview runs.
Concept questions that start simple and get harder.
Follow-ups on every answer, so you explain the why.
One coding challenge in a live editor.
Your report scores technical correctness, problem-solving & tradeoffs, communication clarity, with quotes from your answers as proof.
Questions.
What React questions come up most?
Expect questions on why a component renders again and the rules of hooks. When useEffect runs and why lists need keys come up a lot. Senior roles add speed tools like memo.
How does an Orin mock interview work?
You talk with Orin by voice, like a video call. It asks questions, listens and asks follow-ups based on what you said. Coding happens in a live editor and design on a live whiteboard. After the interview you get a report with quotes from your answers, what cost you points and what to practice next.
Is it free?
Your first interview is free: a 15-minute round with a short coding exercise. No card needed.
Practice the real thing.
A react developer mock interview by voice, with follow-ups and feedback you can use. First interview free.
Start free interview