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Preparing for a React interview in 2026? This comprehensive guide covers essential React interview questions, from fundamentals to advanced topics like Hooks and performance optimization. You’ll find clear explanations, practical examples, and tips on structuring strong answers. Plus, learn how to get discovered by hiring agents on Parlel while you focus on your job search.
\nReact interview questions often vary by your experience:
\nInterviewers may also ask scenario-based questions or coding exercises to evaluate practical skills.
\nReact components are the building blocks of a React application. They can be:
\nReact.Component.Function components are now preferred, especially with Hooks.
\nJSX is a syntax extension for JavaScript that looks similar to HTML. It allows you to write UI elements declaratively inside JavaScript. Under the hood, JSX compiles to React.createElement calls.
Understanding the difference is key in React interviews.
\nThe Virtual DOM is a lightweight JavaScript representation of the actual DOM. React uses it to efficiently update the UI by diffing the previous and current Virtual DOM trees.
\nReconciliation is React’s process of comparing the new Virtual DOM with the previous one to determine the minimal set of changes needed to update the real DOM. This improves performance by avoiding unnecessary DOM manipulations.
\nKeys help React identify which items have changed, been added, or removed in lists. They should be unique and stable to optimize reconciliation.
\nHooks are functions that let you use React state and lifecycle features inside function components. Built-in Hooks include:
\nuseState and useReducer for state management.useEffect for side effects.useLayoutEffect for layout-related effects.useContext, useMemo, and useCallback.\n\nReact describes Hooks as a way to use React features from components; built-in Hooks include state Hooks such as useState and useReducer and the Effect Hook useEffect.
\n
\nEffect Hooks
\n\nThe legacy Hooks overview states that Hooks must be called at the top level, not inside loops, conditions, or nested functions, and only from React function components or custom Hooks.
\n
\nUsing the Effect Hook – React
useEffect runs after the render is committed to the screen. It’s suitable for data fetching, subscriptions, or synchronizing with external systems.useLayoutEffect runs synchronously before the browser repaints, useful for reading layout and synchronously re-rendering.\n\nuseLayoutEffect fires before the browser repaints, making it suitable for layout measurement; React identifies it as a less commonly used variation of useEffect.
\n
\nEffect Hooks
Custom Hooks are functions that start with use and encapsulate reusable logic. They allow sharing stateful logic between components without changing component hierarchy.
React uses synthetic events that wrap native browser events for cross-browser compatibility. Understanding event pooling and propagation is important.
\nContext provides a way to pass data through the component tree without prop drilling. It’s useful for global state like themes or user authentication.
\nBesides React’s built-in state, libraries like Redux, MobX, or Zustand are common in larger apps. Interviewers may ask about pros and cons or integration strategies.
\nReact.memo optimizes functional components by memoizing rendered output.useMemo caches expensive calculations.useCallback memoizes callback functions to avoid unnecessary re-renders.React supports dynamic import and React.lazy to split code into chunks, improving initial load times.
Interviewers often include practical exercises such as:
\nPractice writing clean, well-structured code and explaining your thought process clearly.
\nUse real-world examples where possible and mention current React versions or features if relevant.
\nPublish your React skills on your Parlel profile to get discovered by hiring managers and AI agents actively searching for candidates with React expertise. Set your profile to open-to-work and optionally run or follow agents watching for jobs matching React skills and interview readiness.
\nCheck out relevant roles and connect with recruiters on Explore and Jobs pages. Parlel helps you get matched while you focus on preparing and applying.
\nCommon questions include React fundamentals (components, props, state), Hooks usage, Virtual DOM and reconciliation, event handling, and performance optimization.
\nProps are read-only inputs passed from parent to child components, while state is internal, mutable data managed within a component.
\nThe Virtual DOM is React’s in-memory representation of the UI. Reconciliation compares Virtual DOM trees to update only the necessary parts of the real DOM efficiently.
\nHooks are functions that let you use React features in function components. Rules include calling Hooks only at the top level and only from React functions or custom Hooks.
\nuseEffect runs after the render is painted and is used for side effects like data fetching. useLayoutEffect runs synchronously before painting and is used for layout measurements.
Dheeraj Kumar, founder building Parlel, an open professional network for people, companies and jobs. Find him on his Parlel profile.
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