you-might-not-need-an-effect

name	you-might-not-need-an-effect
description	Analyze code for useEffect anti-patterns and refactor to simpler alternatives. Use when the user says "you might not need an effect", "check effects", "useEffect audit", or asks to review useEffect usage.
disable-model-invocation	true

You Might Not Need an Effect

Analyze code for useEffect anti-patterns and refactor to simpler, more correct alternatives.

Based on https://react.dev/learn/you-might-not-need-an-effect

Arguments

• scope: what to analyze (default: uncommitted changes). Examples: diff to main, src/components/, whole codebase
• fix: whether to apply fixes (default: true). Set to false to only propose changes.

Workflow

1. Determine scope — get the relevant code:

   • Default: git diff for uncommitted changes
   • If a directory/file is specified, read those files
   • If "whole codebase": search all .tsx/.ts files for useEffect

2. Scan for anti-patterns — check each useEffect against the patterns below

3. Fix or propose — depending on the fix argument:

   • fix=true: apply the refactors, then verify with yarn build && yarn lint && yarn type-check
   • fix=false: list each anti-pattern found with a before/after code suggestion

4. Report — summarize what was found and changed

Anti-Patterns to Catch

1. Deriving state during render (no effect needed)

If you're computing something from existing props or state, calculate it during render.

// ❌ Anti-pattern
const [fullName, setFullName] = useState('');
useEffect(() => {
  setFullName(firstName + ' ' + lastName);
}, [firstName, lastName]);

// ✅ Fix — derive during render
const fullName = firstName + ' ' + lastName;

2. Caching expensive calculations (useMemo, not useEffect)

// ❌ Anti-pattern
const [filtered, setFiltered] = useState([]);
useEffect(() => {
  setFiltered(items.filter(item => item.active));
}, [items]);

// ✅ Fix — calculate during render (useMemo only if profiling shows it's needed)
const filtered = items.filter(item => item.active);

3. Resetting state when props change (use key, not useEffect)

// ❌ Anti-pattern
useEffect(() => {
  setComment('');
}, [postCid]);

// ✅ Fix — use key on the component to reset state
<CommentForm key={postCid} />

4. Fetching data (use bitsocial-react-hooks, not useEffect)

This project uses bitsocial-react-hooks for all data fetching. Never use useEffect + fetch.

// ❌ Anti-pattern
const [comment, setComment] = useState(null);
useEffect(() => {
  fetchComment(cid).then(setComment);
}, [cid]);

// ✅ Fix — use the hook
const { state, ...comment } = useComment({ commentCid: cid });

5. Syncing with external stores (use Zustand, not useEffect)

// ❌ Anti-pattern
const [theme, setTheme] = useState('light');
useEffect(() => {
  const unsub = settingsStore.subscribe((s) => setTheme(s.theme));
  return unsub;
}, []);

// ✅ Fix — use the Zustand store directly
const theme = useSettingsStore((s) => s.theme);

6. Sending analytics / logging (move to event handlers)

// ❌ Anti-pattern — fires on every render, not on user action
useEffect(() => {
  logPageView(pageName);
}, [pageName]);

// ✅ Fix — call in the event handler or route change callback
const navigate = () => {
  logPageView(pageName);
  router.push(path);
};

7. Initializing global singletons (use module scope or lazy init)

// ❌ Anti-pattern
useEffect(() => {
  initializeAnalytics();
}, []);

// ✅ Fix — module-level init (runs once on import)
if (typeof window !== 'undefined') {
  initializeAnalytics();
}

Project-Specific Replacements

useEffect pattern	Replace with
Fetch data	useComment, useFeed, useCommunity, etc. from bitsocial-react-hooks
Sync shared state	Zustand store in src/stores/
Derive values from state	Calculate during render
Boolean loading/error flags	state field from bitsocial-react-hooks, or state machine in Zustand

When useEffect IS Appropriate

Not every effect is wrong. Keep useEffect for:

• Subscribing to browser APIs (resize, intersection observer, etc.) with proper cleanup
• Synchronizing with non-React systems (third-party widgets, imperative DOM)
• Running code on mount that genuinely has no hook equivalent