React.js
1. What is React.js?
Answer:
React.js is a popular JavaScript library used for building user interfaces and single-page applications. It helps developers create fast, interactive, and dynamic websites using reusable components. React updates webpage content without refreshing the entire page. It is developed by Meta (Facebook) and widely used in modern web development.
2. What is JSX in React?
Answer:
JSX stands for JavaScript XML and is used in React applications. It allows developers to write HTML-like syntax inside JavaScript code. JSX makes React code cleaner, easier to read, and simple to maintain. React converts JSX into normal JavaScript internally before rendering the webpage.
3. What is a Component in React?
Answer:
A component is a reusable block of code used to build user interfaces in React. Components help divide applications into smaller and manageable parts. Each component works independently and improves code organization. Reusable components reduce duplicate code and speed up development.
4. What is State in React?
Answer:
State is an object used to store dynamic data inside React components. When state values change, React automatically updates the user interface. State helps create interactive applications like counters, forms, and dashboards. React mainly manages state using the useState Hook.
5. What are Props in React?
Answer:
Props are used to pass data from one React component to another. They help create reusable and dynamic components in applications. Props are read-only and mainly used for parent-to-child communication. They improve flexibility and code reusability in React projects.
6. What is Virtual DOM?
Answer:
Virtual DOM is a lightweight copy of the real DOM used internally by React. It improves application performance by updating only changed elements instead of refreshing the whole webpage. This makes React applications faster and more efficient. Virtual DOM is one of the major advantages of React.js.
7. What is useState Hook?
Answer:
useState is a React Hook used to create and manage state in functional components. It allows developers to store dynamic data inside components easily. Whenever the state changes, React updates the UI automatically. useState is commonly used for counters, forms, and toggle buttons.
8. What is useEffect Hook?
Answer:
useEffect is a React Hook used for performing side effects inside components. It is mainly used for API calls, timers, data fetching, and lifecycle operations. useEffect runs after the component renders on the screen. It helps functional components handle tasks similar to lifecycle methods.
9. What is Routing in React?
Answer:
Routing in React allows navigation between multiple pages without reloading the website. It helps create Single Page Applications with smooth user experience. Routing is mainly handled using the React Router library. Users can navigate between pages like Home, About, and Contact quickly.
10. What is React Router?
Answer:
React Router is a library used for handling navigation in React applications. It helps developers create multiple pages inside a single-page application. React Router supports dynamic routing and faster page transitions. It improves navigation and user experience in modern web applications.
11. What is Conditional Rendering in React?
Answer:
Conditional rendering allows React applications to display different content based on conditions. Developers use if statements or ternary operators for conditional rendering. It helps create dynamic and interactive user interfaces. Features like login/logout buttons commonly use conditional rendering.
12. What is Event Handling in React?
Answer:
Event handling in React allows applications to respond to user actions like clicks, typing, and form submissions. React events work similarly to JavaScript events but use camelCase syntax. Event handling improves website interactivity and responsiveness. Functions are commonly used to manage events in React.
13. What is Controlled Component in React?
Answer:
A controlled component is a form element managed using React state instead of the DOM. React controls the input values through state updates. Controlled components help with form validation and better data handling. They are commonly used in login forms and registration forms.
14. What is an Uncontrolled Component in React?
Answer:
An uncontrolled component stores form data directly in the DOM instead of React state. Developers usually access data using refs in uncontrolled components. They are simpler for small forms and quick implementations. However, controlled components are preferred in most modern React applications.
15. What is Fragment in React?
Answer:
A Fragment is used to group multiple elements without adding extra HTML tags to the DOM. It helps create cleaner and optimized HTML structures. Fragments are written using empty tags like <> </>. They improve code readability and avoid unnecessary div elements.
16. What is the use of Key in React?
Answer:
Keys help React identify elements uniquely while rendering lists. They improve rendering performance and prevent unnecessary UI updates. Keys are mainly used inside loops like map() in React. Using unique keys helps React track changes efficiently.
17. What is Lifting State Up in React?
Answer:
Lifting state up means moving shared state to the nearest common parent component. It helps multiple components share and access the same data. This improves communication between sibling components. Lifting state up also prevents duplicate state management.
18. What is Context API in React?
Answer:
Context API is used for sharing data globally across React components without prop drilling. It helps manage global data like themes, authentication, and language settings. Context API improves code structure and simplifies data sharing. It is useful for medium-sized React applications.
19. What is useRef Hook?
Answer:
useRef is a React Hook used to directly access DOM elements and store mutable values. It helps avoid unnecessary re-rendering of components. useRef is commonly used for focusing input fields and managing timers. It is useful for direct DOM manipulation in React.
20. What is Single Page Application (SPA)?
Answer:
A Single Page Application loads a single HTML page and updates content dynamically without full page reloads. SPAs provide faster navigation and smoother user experiences. React.js is widely used for building SPA applications. Popular applications like Gmail and Facebook use SPA architecture.
