Even in the hooks era, interviewers ask about class lifecycle methods to see if you understand when side effects belong. Know the mapping to useEffect and friends.
Common Interview Questions
Q: Name the three lifecycle phases
Answer: Mounting (first render), updating (props/state change), and unmounting (component removed). Each has associated methods like componentDidMount, componentDidUpdate, and componentWillUnmount.
Q: componentDidMount vs useEffect empty deps?
Answer: Both run after paint. componentDidMount fires once after first mount. useEffect(() => {}, []) runs after first render and is the hooks equivalent for mount-only effects.
Q: Why was componentWillMount deprecated?
Answer: Async rendering and Strict Mode made it unsafe for side effects and subscriptions. Data fetching moved to componentDidMount or later to hooks/useEffect.
Q: getDerivedStateFromProps use case?
Answer: Rare — sync state derived from props when you need local state mirroring props changes (e.g., controlled input reset). Prefer fully controlled components or keys to reset state.
Key Points for Interviews
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Map lifecycle to hooks for modern answers
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Fetch data in mount effect, not render
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Cleanup subscriptions in unmount
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getSnapshotBeforeUpdate for DOM measurements before paint
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Strict Mode double-invokes effects in development