Should I store computed values in state?
No. If a value can be computed from props or existing state, compute it during render instead of storing it. Storing derived values creates synchronization bugs when the source changes.
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More FAQs in Props vs State in React: When to Use Which
Ask who owns and changes the data. If the value comes from outside the component and is read-only, it is props. If the component owns the data and needs to change it over time, it is state.
Copying a prop into state is usually a mistake because the two can drift apart. If the value needs to change, the parent should keep it in state and pass it down as a prop with a callback to update it. This is the controlled component pattern.
State is owned by the component that declares it with useState. If multiple components need the same state, lift it to their common parent and pass it down as props, possibly with callbacks to update it.
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