react-useeffect

SKILL.md

Effects are an escape hatch from React. They let you synchronize with external systems. If there is no external system involved, you shouldn't need an Effect.

| Derived state from props/state | useState + useEffect | Calculate during render | | Expensive calculations | useEffect to cache | useMemo | | Reset state on prop change | useEffect with setState | key prop | | User event responses | useEffect watching state | Event handler directly |

| Notify parent of changes | useEffect calling onChange | Call in event handler | | Fetch data | useEffect without cleanup | useEffect with cleanup OR framework |

React useEffect best practices. Use when writing Effects, derived values, or data fetching. Teaches when NOT to use Effects and better alternatives like useMemo or key props. Source: nweii/agent-stuff.

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