Why is fetching in the render body bad?
Because it runs on every render, causing repeated network requests, leaks, and inconsistent state. Fetching is a side effect and belongs in useEffect with the correct dependency array.
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More FAQs in Common React Performance Mistakes That Slow Down Your App
Because memoization itself costs something. Wrapping everything in useMemo and useCallback without measuring adds overhead without benefit. Measure first, then memoize only where there is a real performance issue.
Because you are passing new object or function references on every render. Children compare props by reference, so new references cause re-renders even when the values are the same. Stabilize references with useMemo and useCallback where it matters.
Virtualize it. Rendering thousands of items at once is slow. Use a virtualization library like react-window to render only the visible items, which dramatically improves performance.
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