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 are the features of React?
React framework gaining quick popularity as the best framework among web developers. The main features of React are:
- JSX
- Components
- One-way Data Binding
- Virtual DOM
- Simplicity
- Performance
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. Why we use JSX?
- It is faster than regular JavaScript because it performs optimization while translating the code to JavaScript.
- Instead of separating technologies by putting markup and logic in separate files, React uses components that contain both.
- t is type-safe, and most of the errors can be found at compilation time.
- It makes easier to create templates.
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 an event in React?
An event is an action which triggers as a result of the user action or system generated event like a mouse click, loading of a web page, pressing a key, window resizes, etc. In React, the event handling system is very similar to handling events in DOM elements. The React event handling system is known as Synthetic Event, which is a cross-browser wrapper of the browser's native event.
Handling events with React have some syntactical differences, which are:
- React events are named as camelCase instead of lowercase.
- With JSX, a function is passed as the event handler instead of a string.
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 the difference between Real DOM and Virtual DOM?
The following table specifies the key differences between the Real DOM and Virtual DOM:
The real DOM creates a new DOM if the element updates.
| Real DOM | Virtual DOM |
|---|---|
| The real DOM updates slower. | The virtual DOM updates faster. |
| The real DOM can directly update HTML. | The virtual DOM cannot directly update HTML. |
| The virtual DOM updates the JSX if the element updates. | |
| In real DOM, DOM manipulation is very expensive. | In virtual DOM, DOM manipulation is very easy. |
| There is a lot of memory wastage in The real DOM. | There is no memory wastage in the virtual DOM. |
18. What are the biggest limitations of React?
Following is the list of the biggest limitations of React:
- React is just a library. It is not a complete framework.
- It has a huge library which takes time to understand.
- It may be difficult for the new programmers to understand and code.
- React uses inline templating and JSX, which may be difficult and act as a barrier. It also makes the coding complex.
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.
