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
31. What are Props in React?
A. Private variables
B. Component inputs
C. Component outputs
D. Component methods
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Answer: Component inputs
32. How does data flow between components in React using Props?
A. Unidirectional
B. Bidirectional
C. Multidirectional
D. Circular
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Answer: Unidirectional
33. In a class component, how can you initialize the component's state?
A. Using this.state in the constructor
B. Using a separate setState method
C. By directly assigning values to state
D. Using this.props
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Answer: Using this.state in the constructor
34. What is the primary role of the constructor method in a class component?
A. Initializing component state
B. Defining component structure
C. Rendering the component's UI
D. Handling component events
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Answer: Initializing component state
35. In React, can you modify the value of props directly within a component?
A. Yes
B. No
C. Only for functional components
D. Only for class components
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Answer: No
36. What is the recommended way to pass data from a parent component to a child component in React?
A. Using props
B. Using state
C. Using context
D. Using Redux
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Answer: Using props
37. Which type of data is typically stored in component state in React?
A. User input
B. Static configuration
C. Component methods
D. Shared global data
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Answer: User input
38. In React, how can you update the component's state?
A. By directly modifying this.state
B. By invoking setState method
C. By reassigning the state object
D. By using props
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Answer: By invoking setState method
39. What happens when the state of a React component changes?
A. The component re-renders
B. The component becomes unresponsive
C. The component is deleted
D. The component state becomes immutable
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Answer: The component re-renders
40. What is one key advantage of using props and state in React components?
A. Improved performance
B. Component reusability
C. Tighter security
D. Server-side rendering
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Answer: Component reusability
