React.js, often simply called React, is a highly popular JavaScript library for building user interfaces. Developed and maintained by Facebook, React is renowned for its component-based architecture and the ability to efficiently update and render components when data changes. It is a foundational tool for developing modern web and mobile applications, allowing developers to create dynamic and interactive user interfaces with ease. React's vast ecosystem, including tools like React Native for mobile app development, makes it a top choice for frontend development and a key player in the world of web technologies.
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Practice Test
1. What is React.js primarily used for?
A. Server-side scripting
B. Front-end web development
C. Mobile app development
D. Database management
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Answer: Front-end web development
2. Who developed React.js?
A. Google
B. Facebook
C. Microsoft
D. Amazon
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Answer: Facebook
3. Which programming language is commonly used to write React.js applications?
A. Ruby
B. Python
C. JavaScript
D. PHP
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Answer: JavaScript
4. What is the term used to describe React's ability to update only changed parts of the user interface?
A. Efficient Rendering
B. Dynamic Reconciliation
C. Virtual DOM
D. Component Reusability
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Answer: Virtual DOM
5. What is JSX in React.js?
A. A JavaScript library
B. A file extension for React components
C. A syntax extension for JavaScript
D. A server-side rendering technology
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Answer: A syntax extension for JavaScript
6. Which virtual DOM library is used by React.js?
A. jQuery
B. Vue.js
C. ReactDOM
D. Redux
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Answer: ReactDOM
7. What is the primary function of ReactDOM in a React application?
A. State management
B. Virtual DOM manipulation
C. Server-side rendering
D. Routing and navigation
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Answer: Virtual DOM manipulation
8. In React, what are components?
A. Functional units of code
B. Web browsers
C. Mobile devices
D. Server-side scripts
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Answer: Functional units of code
9. What is the purpose of React Native?
A. Server-side rendering
B. Developing web applications
C. Building native mobile apps
D. Running JavaScript on the server
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Answer: Building native mobile apps
10. Which of the following is NOT a core concept of React?
A. Component-based architecture
B. Unidirectional data flow
C. Two-way data binding
D. Virtual DOM
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Answer: Two-way data binding
