🧒 Explain like I'm 5
Imagine you are solving a difficult problem. useMemo = writing the answer on paper so you don't have to calculate it again next time. useCallback = keeping the same formula sheet instead of rewriting an identical one each time. React.memo = putting a sticky note on the child's door: "if the problem doesn't change, no need to redo it."
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Senior-level deep dive: internals, pitfalls, and a self-interview ladder.
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