useState, useEffect, useRef, useMemo, useCallback, useContext, useReducer, custom hooks and rules of hooks.
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- What does useState return?
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An array with the state value and a setter function- How do you update state with useState?
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Call the setter function with the new value- When does useEffect run if the dependency array is empty?
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Only once after the initial render (on mount)- When does useEffect run if you omit the dependency array?
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After every render- What is a cleanup function in useEffect?
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A function returned from useEffect that runs before the effect re-runs or on unmount- What does useRef return?
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A mutable object with a .current property- Does updating a ref cause a re-render?
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No, updating a ref does not trigger a re-render- Name a common use case for useRef
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Storing a reference to a DOM element or accessing it directly- What is the primary purpose of useMemo?
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To memoize a computed value and avoid recalculating it on every render- When should you use useMemo?
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When you have an expensive computation that does not need to run every render- What is the primary purpose of useCallback?
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To memoize a function definition so it maintains the same reference across renders- Why would you use useCallback?
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To prevent unnecessary re-renders of child components that depend on the function reference- What does useContext do?
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Allows a component to access context values without prop drilling- What must you do before using useContext?
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Create a context using React.createContext()- When should you use useReducer instead of useState?
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When you have complex state logic or multiple related state updates
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