React Interview Masterclass: Top 200 Questions (+PDF) (2026)

Explore the basics of React, including what it is, its features, virtual dome components, and the single-page application concept.

Explore how React fits into software development, from front-end UI to back-end data flows, and why React's reusable components simplify building single-page applications.

Discover the seven key features of React: virtual dom, component-based architecture, reusability and composition, JSX, and declarative syntax. Enable React hooks to leverage these features and the community ecosystem.

Define the document object model as a tree-like representation of a web page that JavaScript uses to dynamically access and manipulate HTML content and structure.

Demonstrate how virtual dome mirrors the real dome to enable selective updates, and explain the difference between dome and virtual dome, plus reconciliation that speeds React UI updates.

Explore React components as reusable building blocks that structure a web page, with header, menu, and footer as examples, and learn the basics: import, functional component, JSX, and export.

Explain how a single page application updates content dynamically on one page without full page reloads, using YouTube as an example.

Discover React's five key advantages: component-based architecture enables reusable UI, fast performance from the virtual DOM, cross-platform open source status, compatibility with other frameworks and libraries, and a large community.

React shines for managing many small, replaceable components, but for very small static sites with fixed content, plain HTML, CSS, and JavaScript avoid the learning curve and setup time.

Explore the role of JSX in React as JavaScript XML and its conversion to JavaScript by Babel for browsers. Learn why JSX is easier to read and write than React.createElement.

Explore the difference between declarative and imperative syntax in react, highlighting how jsx emphasizes output over steps and contrasts with pure javascript element creation.

Strengthen your React fundamentals with the second basics lecture, covering arrow functions, main files in React projects, and how a React app loads to prepare for interviews.

Explain how arrow function expression in JSX replaces regular function declarations, showing parameters in brackets, arrow operator, and assigning the function to a variable to declare components.

Install NodeJS and a code editor (VS Code), run npx create react app with your project name, then npm start to view your first React project in the browser.

Discover how a React app loads and displays components in the browser by tracing the flow from index.html to index.js, bundle.js, and rendering the app component into the root element.

React is a JavaScript library, while Angular is a UI framework. React uses a virtual dom and relies on external libraries; Angular provides built-in routing, forms validation, and http requests.

Identify other popular front-end js frameworks beyond React, including Angular, Vue.js, AngularJS, Backbone.js, and Ember.js, and note React remains the most popular.

Compare React as a library versus a framework, and learn how React remains a library while gradually moving into framework mode.

Explore how React delivers reusability and composition through a component-based architecture, enabling component reuse, independent development, and minimal impact when updating parts of an app.

Explore state, stateless, and stateful concepts and state management in React, including how components manage and render current data, update state, and the roles of hooks and Redux.

Discover how props in JSX pass data from a parent to a child component, and how to pass parameters and access them as properties like props.name and props.purpose.

Explore ten questions about the main files and folders in a React project, with revision tips to strengthen interview readiness for React interview mastery.

Install dependencies for react projects using npm, which creates the node_modules folder containing the react libraries. Never touch this folder to prevent issues.

Store static assets in the public folder, including index.html, favicon, images, and fonts, served directly to the browser, with no API data fetching, components, or dynamic behavior.

Explain how the src folder stores all the source code and components for a React app, driving the dynamic changes of the web application.

Explain how the index.html in the public folder serves as the static shell of a single-page React app, with the root div replaced by index.js components.

Learn how index.js and ReactDOM render your app into the root div, using createRoot and render to replace the index.html root with the app component.

Explain the role of the app.js file as the root React component, acting as a container for all child components and defining structure, layout, and root routing.

Define a React component with the function keyword, accepting props and returning JSX; components are invoked and rendered to the DOM via index.js and react-dom, with arrow function alternatives.

Learn why a function without a return in App.js can exist, using arrow function expressions with less code. Omitting the return renders nothing in UI, useful for logging.

The export default statement in app.js makes the App component available for import in other files, enabling its use with import statements; removing it breaks imports.

Learn that in React, the file name and the component name do not have to match, though keeping them identical improves organization and readability for quick book revisions.

Learn ten JSX questions, cover what JSX is, its advantages, Babel, fragments, spread operator, and conditional rendering, with tips to elaborate answers and demonstrate practical use from your projects.

Explain how JSX in React is JavaScript XML, converted to JavaScript by the React Babel library, enabling readable and writable code that creates React elements for browsers.

Discover the five advantages of JSX: improved code readability, early error checking with type safety, support for JavaScript expressions, better performance, and code reusability.

Discover how Babel transpiles JSX into JavaScript so browsers understand React code, using the Babel library in node_modules via npm to convert JSX.

Discover how React fragments group a list of children without adding extra nodes, solving JSX root element errors without inserting divs, using <React.Fragment> or empty tags like <></>.

Master the spread operator in JSX to pass a props object from a parent to a child, using three dots to expand arrays or objects.

Explore the four types of conditional rendering in JSX: if-else, ternary operators, the logical and operator, and switch statements, with guidance on when to use each.

Learn how to iterate over arrays in JSX using the map method, with callback and arrow functions, to double each element and render results efficiently.

A browser cannot read a JS file directly. Babel converts the JS into browser-readable code that browsers can understand.

Explore how a transpiler converts code between high-level languages, such as JSX to JavaScript with Babel, and distinguish it from a compiler that targets machine code.

Learn how JSX can run without React, using a custom transpiler like Babel, and why this approach is discouraged due to JSX's tight integration with React and its features.

Master React components by exploring functional and class components through nine interview questions, five on functional and four on class, with tips for confident interview answers.

Explore React components as the reusable building blocks of user interfaces, illustrating a header, menu, and footer within a component-based architecture, and review import, functional components, JSX, and export.

Explore the types of React components, functional and class components, and learn how functional components defined as JavaScript functions or arrow expressions are stateless by default, with hooks enabling state.

Learn how to pass data between functional components in React using props, enabling data flow from a parent to a child component, a crucial interview-ready concept.

Prop drilling in React involves passing props through multiple component layers—from a parent to children and grandchild—to share data across the tree.

Explain why prop drilling is problematic and show five ways to avoid it—using a central store, context API, Redux, component composition, callback functions, and custom hooks.

Explore class components in React, defined as JavaScript classes that extend React's component, return JSX via the render method, and manage state with lifecycle methods.

Pass data between class components using props by setting a message attribute in the parent and reading it in the child with this.props.message.

Learn how the this keyword in class components refers to the class instance. Access properties like message and parent-to-child data, and see what happens when this keyword is removed.

Explore five key differences between functional and class components in React, covering syntax, state with hooks versus this.state, lifecycle methods, readability, and the this keyword and render method.

Explore six routing questions and learn how React routing enables navigation between components, a key skill in the React interview masterclass.

Learn how routing in React enables navigation between components without page refresh, updating the URL in a single-page app. Explore how React Router renders components based on the URL.

Install the router from React library, import routes, route, and link, use link and route components for navigation, and wrap the app in the router in index.js to enable routing.

Explore how the Routes container holds multiple Route components and how each Route defines a path and the component to render when the path matches.

Explore how route parameters in React Router pass dynamic data via the url path to a component, such as a user profile, when a navigation link is clicked.

Explain how the switch component acts as a container for multiple routes, executes only the first matched route, and ignores the rest, enabling not found route handling.

Use the exact prop with the Route component in React routing to restrict matches to the exact path, preventing /about from matching its extensions like /about/t or /about/contact.

Dive into the two essential React hooks, useState and useEffect, through interview-style questions that sharpen your hook knowledge for cracking interviews.

Discover how React hooks empower functional components to manage state and lifecycle, and explore the top hooks like useState, useEffect, useContext, useReducer, useCallback, useMemo, useRef, and useLayoutEffect.

Explore state, stateless, and stateful concepts and state management in React, including how updates affect component data, rendering, and the role of hooks and Redux.

Explore how the useState hook manages state in React, including initial value, array destructuring, and the set function to increment and render updates in the UI.

Master the use effect hook in React to perform side effects in functional components, including data fetching and subscriptions, controlled by the dependency array.

Learn how the dependency array in the useEffect hook triggers re-fetching data and re-rendering the UI when values like user id change.

Explain that an empty array in useEffect makes the effect run only once, because there are no dependencies, so the fetched api data remains fixed.

Explore the first three useContext questions and five useReducer questions in this React interview masterclass lecture, with tips to increase playback speed if you find questions easy.

Learn how the useContext hook eliminates prop drilling by passing data via a context created with createContext, using provider and consumer, with the hook favored for simplicity.

Describe how createContext returns an object with provider and consumer properties, how the provider supplies context to children, and how the consumer or useContext consumes it.

Use the useContext hook to avoid prop drilling and access context values in deeply nested components; apply it for theme switching, localization, centralized settings, user preferences, and notifications.

Both useState and useReducer share a similar approach, returning an array with the current state and a function to update it, with useReducer mirroring useState about 70% of the code.

Explain the useReducer hook for managing complex state with a reducer function and an initial state object, using dispatch and action types, contrast it with useState.

Compare the differences between useState and useReducer hooks, presenting a concise revision with a few notes for quick theory refresh and optional book reference.

Explain the dispatch and reducer functions in the useReducer hook, showing how dispatch triggers the reducer to update state via action types.

Passing the initial state as an object in useReducer lets you manage complex multi-property states with reusable reducer functions.

Explore six questions on four React hooks—useCallback, useMemo, useRef, and useLayoutEffect—and learn when to apply them to boost performance while avoiding common pitfalls.

Understand how the useCallback hook memorizes function references in React to prevent unnecessary child rerenders and improve performance, with parent and child examples.

Learn what parameters the useCallback hook accepts and what it returns, including the callback function and the dependencies array that controls when the memorized function is recreated.

Explain how the useMemo hook memorizes the result of an expensive computation to improve performance, using a function and a dependencies array, and re-executes only when dependencies change.

Explore the use ref hook for accessing dom elements and persisting focus across renders, using a ref object's current property to hold values without triggering re-renders.

Compare useLayoutEffect with useEffect, noting useEffect runs after render asynchronously while useLayoutEffect runs synchronously, potentially blocking initial UI rendering during API data fetch and dependency array handling.

Learn when to use use layout effect to handle DOM elements whose styling depends on external API data, ensuring bold styling only after data arrives, unlike use effect.