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 from official docs. Use when writing/reviewing useEffect, useState for derived values, data fetching, or state synchronization. Teaches when NOT to use Effect and better alternatives. Source: fluid-tools/claude-skills.

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