ReactJS interview questions

ReactJS interview questions: Prepare for your ReactJS interview with these 25 comprehensive and original interview questions and answers covering React basics, components, state management, lifecycle methods, hooks, JSX, virtual DOM, and more.

ReactJS Interview Questions and Answers

1. What is ReactJS?

• ReactJS is an open-source JavaScript library maintained by Facebook for building user interfaces or UI components. ReactJS interview questions

1. What are the key features of ReactJS?

• Key features include virtual DOM for efficient updates, component-based architecture, JSX syntax for writing HTML in JavaScript, and uni-directional data flow.

1. Explain the difference between Real DOM and Virtual DOM.

• Real DOM updates the entire HTML structure upon every change, whereas Virtual DOM updates only the changed parts, making updates faster and more efficient.

1. What are components in React?

• Components are reusable UI elements that can contain both logic and UI controls. They can be class components or functional components.

1. What is JSX in React?

• JSX (JavaScript XML) is a syntax extension for JavaScript that allows HTML to be written inside JavaScript code. It simplifies the process of writing React components.

1. What is state in React?

• State is a JavaScript object used to store data that affects a component’s rendering and behavior. It is managed within the component using setState() and can be updated.

1. What are props in React?

• Props (short for properties) are inputs to components that are passed from a parent component. They are read-only and help pass data from one component to another.

1. Explain React lifecycle methods in class components.

• React lifecycle methods are methods that are invoked at various stages of a component’s life cycle, such as componentDidMount, componentDidUpdate, and componentWillUnmount.

1. What are hooks in React?

• Hooks are functions that let you use state and other React features in functional components. Examples include useState, useEffect, useContext, and useReducer.

1. What is the difference between class components and functional components?
   • Class components are ES6 classes that extend React.Component and can have state and lifecycle methods. Functional components are simpler and rely on functions and hooks for state and side effects. ReactJS interview questions
2. How do you create a new React project using Create React App?
   • Use npx create-react-app project-name to set up a new React project with Create React App, a tool for bootstrapping React applications.
3. What is the purpose of useState hook in React?
   • The useState hook allows functional components to have state variables. It returns a stateful value and a function to update it, preserving the state between re-renders.
4. How does data flow in React?
   • Data flows in React in a unidirectional manner: parent components pass props down to child components, and child components can send data or events back to parent components using callbacks.
5. What are higher-order components (HOCs) in React?
   • Higher-order components are functions that take a component and return a new component with enhanced functionality. They enable code reuse, logic abstraction, and props manipulation. ReactJS interview questions
6. Explain the concept of keys in React lists.
   • Keys are special string attributes used by React to identify which items have changed, are added, or are removed in lists. They help optimize rendering and maintain component state.
7. What is Redux, and how does it work with React?
   • Redux is a predictable state container for JavaScript applications. It helps manage the global state of an application and works seamlessly with React using the react-redux library.
8. How do you handle forms in React?
   • Forms in React are handled by using controlled components where form data is controlled by React state. Use events like onChange to update state and manage form inputs.
9. Explain React Router.
   • React Router is a popular library for routing in React applications. It enables navigation between different components in the application without a full-page refresh.
10. What are React fragments?
    • React fragments allow you to return multiple elements from a component’s render method without adding extra nodes to the DOM. They are denoted by <React.Fragment> or shorthand <>. ReactJS interview questions
11. What are React hooks rules?
    • Hooks must be called at the top level of a functional component, not inside loops, conditions, or nested functions. They are prefixed with use to indicate their purpose (e.g., useState, useEffect).
12. Explain the useEffect hook in React.
    • useEffect is a hook that allows functional components to perform side effects (such as data fetching, subscriptions, or DOM manipulation) after render.
13. What are the advantages of using React over other frameworks?
    • React offers a virtual DOM for better performance, component-based architecture for reusability, a strong community and ecosystem, and JSX for writing declarative UIs in JavaScript.
14. How can you optimize React applications?
    • Optimize React applications by using the React DevTools for profiling, implementing code splitting and lazy loading, minimizing the use of unnecessary re-renders, and optimizing state management.
15. What tools can you use for debugging React applications?
    • Use browser developer tools (e.g., Chrome DevTools) for inspecting the virtual DOM, monitoring component state and props, and debugging JavaScript. React DevTools extension provides additional insights into component hierarchy and state.
16. How do you deploy a React application?
    • Deploy a React application by creating a production build (npm run build) and deploying the generated static files to a web server or hosting platform like Netlify, Vercel, AWS S3, or GitHub Pages. ReactJS interview questions

These questions cover a wide range of topics essential for ReactJS interviews and should help you prepare thoroughly.

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