Top most asked ReactJS Questions in Interviews.

ReactJS Interview Questions and Answers

This document provides a comprehensive list of ReactJS interview questions, along with links to additional resources for further learning.

1. What is React? React is a JavaScript library for building user interfaces (UIs), primarily for single-page applications. It's known for its component-based architecture and efficient rendering using a Virtual DOM.

2. What are the advantages of using React? Advantages include: component reusability, improved performance (Virtual DOM), ease of learning (JSX), large community support, and a vast ecosystem of tools and libraries.

3. What are the limitations of using React? Limitations can include: the steep learning curve for complex applications, SEO challenges (though mitigatable), and the need for additional libraries for routing and state management in larger projects.

4. What is useState() in React? useState() is a React Hook that lets functional components manage state. It returns an array containing the current state value and a function to update it.

5. What are keys in React? Keys are special string attributes that you provide to the children of components that are rendered in lists. React uses keys to identify which items have changed, are added, or are removed. They're crucial for efficient updates and preventing unexpected behavior.

6. What is JSX? JSX (JavaScript XML) is a syntax extension to JavaScript that allows you to write HTML-like code within your JavaScript code. It makes React code more readable and easier to maintain.

7. What is the difference between functional and class components? Functional components are simpler, often using Hooks for state and lifecycle management. Class components are more complex, using this to access state and lifecycle methods. Functional components are generally preferred for their simplicity and readability.

8. What is Virtual DOM? The Virtual DOM is a lightweight in-memory representation of the actual DOM. React uses it to efficiently update the real DOM, minimizing direct manipulations and improving performance.

9. What are props in React? Props (properties) are data passed from a parent component to a child component. They're immutable – you can't change them within the child component.

10. Explain React state and props. State is internal data managed by a component that can change over time, causing the component to re-render. Props are external data passed to a component; they are read-only within the component.

11. Explain about the types of side effects in React. Side effects are actions that a component performs that affect things outside of itself, such as fetching data, manipulating the DOM directly, or setting timers. They are managed using the useEffect Hook.

12. What is prop drilling in React? Prop drilling is the practice of passing props down through multiple levels of components in a component tree just to reach a component that needs the data. It makes code less maintainable and harder to refactor.

13. What are React Hooks? Hooks are functions that let you “hook into” React state and lifecycle features from within functional components. Examples include useState, useEffect, useContext, etc.

14. What is the use of useEffect() hook? useEffect is a Hook that lets you perform side effects in functional components. This includes data fetching, subscriptions, and manually changing the DOM.

15. What is ref in React? A ref is a mechanism to directly access a DOM element or a component instance. It's useful for tasks like focusing an input element or directly manipulating the DOM.

16. Explain strict mode in React. Strict mode is a tool for highlighting potential problems in an application. It doesn't render any visible UI changes but activates additional checks and warnings during development.

17. How to prevent re-render in React? Techniques include using React.memo for memoizing components, using useCallback to memoize callbacks, and optimizing state updates to avoid unnecessary re-renders.

18. Name few techniques to optimize React app performance. Techniques include code splitting, lazy loading, memoization, using React.memo, and optimizing state updates.

19. How to pass data between React components? Data can be passed down through props, up through callbacks, or using context for global state management.

20. What are higher-order components? Higher-order components (HOCs) are functions that take a component as an argument and return a new enhanced component. They are a pattern for reusing component logic.

21. What are different phases of the component life cycle? For class components: mounting, updating, and unmounting. For functional components, the lifecycle is managed using Hooks.

22. What is React Router? React Router is a library for adding client-side routing to React applications. It allows you to create single-page applications with multiple views.

23. Explain Conditional rendering in React. Conditional rendering is a technique to render different UI elements based on certain conditions. This can be achieved using if statements, ternary operators, or short-circuit evaluation.

24. How to pass data between sibling components using React Router? Sibling components typically don't communicate directly. Instead, data is usually passed up to a parent component and then down to the other sibling. Context API can also be used.

The above is the detailed content of Top most asked ReactJS Questions in Interviews.. For more information, please follow other related articles on the PHP Chinese website!