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
41. In React, what is the first method called during the component lifecycle?
A. componentDidMount
B. render
C. componentWillUnmount
D. constructor
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Answer: constructor
42. Which lifecycle method is commonly used to fetch data from an API in a React component?
A. componentDidMount
B. componentWillUnmount
C. componentWillMount
D. render
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Answer: componentDidMount
43. Which lifecycle method should be used to perform cleanup when a component is unmounted?
A. componentDidMount
B. componentWillUnmount
C. componentWillMount
D. render
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Answer: componentWillUnmount
44. What is the primary purpose of the render method in a React component?
A. To fetch data from an API
B. To render the component's UI
C. To clean up resources when unmounting
D. To update component state
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Answer: To render the component's UI
45. Which method is invoked just before a component is removed from the DOM?
A. componentWillUnmount
B. componentDidMount
C. componentWillMount
D. render
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Answer: componentWillUnmount
46. In React, which lifecycle method is called when a component receives new props?
A. componentWillUpdate
B. componentWillReceiveProps
C. componentDidUpdate
D. render
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Answer: componentWillReceiveProps
47. What is the primary difference between componentWillReceiveProps and static getDerivedStateFromProps?
A. They are the same method
B. componentWillReceiveProps is deprecated
C. static getDerivedStateFromProps is static
D. static getDerivedStateFromProps is called before rendering
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Answer: static getDerivedStateFromProps is called before rendering
48. Which lifecycle method is recommended for performing side effects, such as data fetching, in a class component?
A. componentDidMount
B. componentDidUpdate
C. componentWillReceiveProps
D. componentWillUnmount
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Answer: componentDidMount
49. In functional components, which React hook replaces lifecycle methods like componentDidMount?
A. useEffect
B. useState
C. useLifecycle
D. useComponent
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Answer: useEffect
50. What is the purpose of the shouldComponentUpdate lifecycle method?
A. To check if a component should re-render
B. To update the component's state
C. To fetch data from an API
D. To render the component's UI
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Answer: To check if a component should re-render
