react-useeffect-avoid

React: Avoid useEffect

Goal

Use useEffect only to sync with external systems. Keep pure React logic in render or event handlers.

Rules

• Use effects for subscriptions, timers, browser APIs, third-party libraries, analytics, and document title updates.
• Calculate derived state during render.
• Handle user actions in event handlers.
• Reset child state with a key.
• Use useSyncExternalStore for external stores.
• Use query libraries for server data when available.
• Do not use effects as general state management.
• Do not use effects to copy props into state unless there is a real reset model.

Flow

1. Ask: is there an external system?
2. If yes, use effect with cleanup.
3. If derived value, calculate during render.
4. If user-triggered, use event handler.
5. If reset needed, use key.
6. If shared external state, use useSyncExternalStore.
7. If async server data, prefer existing data library.

Alternatives

• Derived state: compute during render.
• Expensive derived state: useMemo.
• Form submit: async submit handler.
• Prop-based reset: key remount.
• Event side effect: event handler.
• Server data: framework loader, TanStack Query, SWR, or Suspense.

Pattern

useEffect(() => {
  const connection = createConnection(roomId);
  connection.connect();
  return () => connection.disconnect();
}, [roomId]);

References

• context/anti-patterns.md: detailed effect mistakes.
• context/patterns-to-avoid.md: common patterns to replace.
• context/decision-tree.md: expanded decision guide.
• React Docs: You Might Not Need an Effect
• React Docs: Synchronizing with Effects

Output

• Keep, remove, or replace effect.
• External system named when effect remains.
• Replacement pattern when effect is unnecessary.