1. What is React JS?

React JS is an open-source JavaScript library developed by Facebook for building fast and interactive user interfaces, especially for Single Page Applications (SPAs).

React uses reusable components and a Virtual DOM to improve application performance. It is widely used by companies such as Facebook, Instagram, and WhatsApp.

2. What are the features of React JS?

Some key features of React JS include:

• Component-Based Architecture
• Virtual DOM for faster rendering
• Reusable UI Components
• High Performance
• One-Way Data Binding
• JSX Syntax
• Improved SEO Support
• Easy Integration with Other Libraries
• Strong Community Support

3. How is React JS different from other JavaScript frameworks?

React differs from other frameworks because it is a JavaScript library focused only on building user interfaces.

Unlike Angular, React:

• Focuses only on the View layer.
• Uses reusable components.
• Uses Virtual DOM for better performance.
• Supports one-way data flow.
• Can be integrated with other libraries for routing and state management.

4. What are the lifecycle phases of React JS?

The main lifecycle phases of React components are:

• Initialization
• Mounting
• Updating
• Unmounting

These lifecycle methods help manage component creation, updates, and removal.

5. When was React JS released?

React JS was officially released by Facebook in March 2013.

6. What is Redux?

Redux is a predictable state management library used with React applications.

It helps manage application state in a centralized store, making applications easier to develop, test, and maintain, especially for large-scale projects.

7. What is Redux Thunk?

Redux Thunk is middleware that allows action creators to return functions instead of plain action objects.

It is commonly used to handle:

• Asynchronous API calls
• Delayed actions
• Conditional dispatching

Redux Thunk enables better handling of asynchronous operations in React applications.

8. What is Flux?

Flux is an application architecture that follows unidirectional data flow.

It helps manage data movement between components, making applications more predictable and easier to maintain.

The main parts of Flux include:

• Actions
• Dispatcher
• Stores
• Views

9. What is the official repository URL of React JS?

The official GitHub repository for React JS is:

https://github.com/facebook/react

10. What are the limitations of React JS?

Some limitations of React include:

• It is only a UI library, not a complete framework.
• Learning JSX may be challenging for beginners.
• Frequent updates require developers to stay updated.
• Additional libraries are needed for routing and state management.
• Initial project setup can be complex for beginners.

11. What is State in React?

State is an object that stores dynamic data within a component.

It controls how a component behaves and renders.

When the state changes, React automatically updates the user interface to reflect the latest data.

12. What are the disadvantages of React?

Some disadvantages include:

• Steeper learning curve for beginners.
• Requires additional libraries for complete application development.
• JSX syntax may be unfamiliar to new developers.
• Rapid updates require continuous learning.
• Project structure can vary between developers.

13. Why can’t browsers read JSX directly?

Browsers understand only standard JavaScript.

JSX is a JavaScript syntax extension that must be converted into regular JavaScript using tools like Babel before it can be executed by the browser.

14. When should you use Refs in React?

Refs are commonly used for:

• Accessing DOM elements directly
• Managing input focus
• Selecting text
• Playing audio or video
• Triggering animations
• Integrating with third-party DOM libraries

Refs provide a way to interact directly with DOM elements when needed.

15. Why is React JS so popular?

React JS has become one of the most popular frontend libraries because it offers:

• High performance through Virtual DOM
• Reusable components
• Faster UI rendering
• Easy maintenance
• Strong community support
• Excellent scalability
• Rich ecosystem of libraries and tools
• Wide industry adoption by leading technology companies