Fix React setState Warning in useEffect Next.js 16

The React warning “Calling setState synchronously within an effect can trigger cascading renders” hits hard in Next.js 16.0.7 with React 19.2.0, thanks to the stricter eslint-plugin-react-compiler rules flagging potential performance pitfalls in useEffect. Wrap synchronous setState calls inside useEffectEvent to extract logic without stale closures, or refactor to batch updates and derive state outside effects where possible. For multiple state updates in useEffect—like useState useEffect React patterns—leverage React 19’s automatic batching, proper deps, and avoid loops by syncing external data smartly.

Contents

• Understanding the Warning
• Why It Happens in Next.js and React 19
• Fix 1: Wrap in useEffectEvent
• Fix 2: Refactor Effects and Batch Updates
• Handling Multiple State Updates
• Best Practices to Avoid Performance Issues
• Sources
• Conclusion

Understanding the Warning

Ever seen your console light up with “Calling setState synchronously within an effect can trigger cascading renders”? It’s React 19’s way of nudging you toward better code. This warning comes from the new eslint-plugin-react-compiler, which spots setState calls directly in useEffect bodies. Why? Because they can kick off chains of re-renders, tanking performance—especially in apps with heavy hydration like Next.js.

Picture this: your effect runs, updates state, component re-renders, effect runs again. Cascade city. The official React docs call it out clearly: synchronous setState in effects skips batching benefits and risks infinite loops if deps aren’t perfect. In React 19.2.0, batching got smarter—even across promises—but this rule stays strict to catch sloppy patterns.

And in Next.js 16.0.7? Hydration mismatches amplify it. Client-side localStorage grabs or theme syncs often trigger it, as devs reach for quick setState fixes post-mount.

Why It Happens in Next.js and React 19

Next.js loves server-side rendering, but client hydration needs client-only data—like user prefs from localStorage. Boom: useEffect with setState. React 19 flags it because older habits don’t fly anymore.

Community threads nail it. On GitHub React issues, devs debate: the rule’s overly strict for “didMount” patterns, yet it prevents real loops. Reddit discussions echo this—especially with Next.js themes or caches, where setState hydrates mismatches.

React 19 batches state updates in the same event tick automatically, per React’s optimization guide. But effects bypass that if you’re not careful. Multiple setState calls? They might batch now, but the linter doesn’t trust you yet.

Short story: it’s not always a bug. Sometimes it’s your hydration workaround. But ignoring it? Risky.

Fix 1: Wrap in useEffectEvent

React’s gift to you: useEffectEvent. It’s a Hook for pulling non-reactive logic out of effects into a fresh function. Call it inside useEffect, and it always sees latest props/state—no stale closures.

Here’s how. Say you’ve got:

import { useState, useEffect } from 'react';

function MyComponent() {
 const [data, setData] = useState(null);
 const [loading, setLoading] = useState(true);

 useEffect(() => {
 // This triggers the warning
 setData(localStorage.getItem('data'));
 setLoading(false);
 }, []);

 // ...
}

Wrap the updater:

import { useEffectEvent } from 'react';

function MyComponent() {
 const [data, setData] = useState(null);
 const [loading, setLoading] = useState(true);

 const updateData = useEffectEvent(() => {
 setData(localStorage.getItem('data'));
 setLoading(false);
 });

 useEffect(() => {
 updateData(); // No warning!
 }, []);

 // ...
}

The React docs stress: define it right before the effect, call only inside effects. No passing to kids. GitHub confirms: it dodges the lint rule perfectly.

Pro tip: for Next.js hydration, this shines. Server skips localStorage; client runs effect safely.

Fix 2: Refactor Effects and Batch Updates

Not every setState needs an effect. Ask: can you derive it? React 19 pushes “you might not need an effect.” Compute inline if possible.

Multiple updates? Batch 'em in one handler:

const [data, setData] = useState(null);
const [loading, setLoading] = useState(true);

useEffect(() => {
 const newData = localStorage.getItem('data');
 setData(newData);
 setLoading(false); // Batches with above in React 19
}, []);

Still warns? Derive state:

const hydratedData = typeof window !== 'undefined' ? localStorage.getItem('data') : null;
const [data, setData] = useState(hydratedData);

No effect needed. Medium post shows cascading renders from unbatched calls—refactor kills it.

For loops: add all deps. ESLint whines about missing ones anyway. Or disable per-line: // eslint-disable-next-line react-hooks/set-state-in-effect.

Next.js specifics? next-themes issue suggests off-ing the rule if it’s hydration-only. But fix first.

Handling Multiple State Updates

Got three setState in one useEffect? React 19 batches them automatically in event handlers or effects—same tick, one render. But linter flags synchronous ones.

Best play: group related updates.

useEffect(() => {
 const updates = () => {
 setLoading(true);
 setData(fetchData());
 setError(null);
 };
 updates();
}, [deps]);

Still picky? useEffectEvent the whole batch. Or use useSyncExternalStore for external syncs like localStorage—React recommends it over effects.

Another GitHub thread hits Next.js cache woes: same warning, same fix—batch or event-ify.

Test it: log renders. Multiple setState? One log if batched. Performance win.

What if async? Await inside effect, but batch post-await carefully. React handles it.

Best Practices to Avoid Performance Issues

Don’t just silence—optimize.

1. Derive when possible. State from props? Inline calc.
2. Minimal deps. Exhaustive? useEffectEvent or memoize.
3. useSyncExternalStore for externals. localStorage, timers—perfect fit.
4. Batch handlers. onClick with multiple setState? One render.
5. Lint wisely. Off for legit hydration, but rare.

In Next.js 16: use useEffect post-hydration sparingly. Client components help.

React Compiler GitHub admits false positives—they’re tweaking. Till then, these keep you fast.

Quick win? Profile with React DevTools. Spot cascades, refactor.

Sources

1. useEffectEvent – React
2. You Might Not Need an Effect – React
3. Bug: react-hooks/set-state-in-effect overly strict? · Issue #34743 · facebook/react
4. Error: Calling setState synchronously within an effect can trigger cascading renders | Medium
5. r/react on Reddit: Calling setState synchronously within an effect
6. [cacheComponents] Activity component route preservation · Issue #86577 · vercel/next.js
7. Bug: react-hooks/set-state-in-effect ESLint error · next-themes #374
8. [Compiler Bug]: useEffectEvent bypasses lint rule · Issue #35390 · facebook/react

Conclusion

Tame that React useEffect setState warning by prioritizing useEffectEvent for tricky logic, refactoring to derive state, and leaning on React 19’s batching for multiple updates—no more cascades in your Next.js app. You’ll dodge performance hits and keep ESLint happy. Bottom line: effects for side effects only; everything else, compute smartly. Your renders will thank you.