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
21. What does JSX stand for in React development?
A. JavaScript Extension
B. JavaScript XML
C. JavaScript Execution
D. JavaScript Framework
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Answer: JavaScript XML
22. What is JSX primarily used for in React?
A. Defining component styles
B. Defining component structure
C. Handling server-side logic
D. Managing database queries
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Answer: Defining component structure
23. Is JSX mandatory to use when building React components?
A. Yes
B. No
C. Only for class components
D. Only for functional components
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Answer: Yes
24. How does JSX differ from regular HTML?
A. JSX uses angle brackets (<>)
B. JSX uses camelCase for attributes
C. JSX uses double curly braces ({{}})
D. JSX uses square brackets ([])
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Answer: JSX uses camelCase for attributes
25. What is the main role of Babel in the context of JSX?
A. Handling database queries
B. Converting JSX into JavaScript
C. Managing component styles
D. Parsing XML documents
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Answer: Converting JSX into JavaScript
26. In JSX, how do you render a JavaScript expression within curly braces?
A. {{ expression }}
B. { expression }
C. () expression
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Answer: { expression }
27. What is the purpose of using the className attribute in JSX instead of class?
A. To apply inline styles
B. To define component structure
C. To reference CSS classes
D. To create custom components
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Answer: To reference CSS classes
28. In JSX, how do you render a component that you've defined elsewhere?
A. <Component />
B. {Component}
C. {{Component}}
D. [Component]
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Answer: <Component />
29. What happens when JSX is transpiled by tools like Babel?
A. JSX is converted to HTML
B. JSX is converted to JavaScript
C. JSX is executed directly in the browser
D. JSX is compiled to WebAssembly
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Answer: JSX is converted to JavaScript
30. Which of the following is a valid JSX element in React?
A. <div class="container"></div>
B. <p>{text}</p>
C. <h1>[title]</h1>
D. console.log('Hello, React!')
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Answer: <p>{text}</p>
