Fix: Next.js Hydration Mismatch Errors
Quick Answer
Wrap client-only code (window, localStorage, browser APIs) in useEffect or use the 'use client' directive. Common cause: rendering dates, random values, or browser-dependent content during SSR.
Quick Fix Summary
| Issue | Hydration errors |
| Fastest fix | Identify the mismatch |
| Use this page if | Console shows 'Hydration failed' or 'Text content did not match' |
Symptoms
- !Console shows 'Hydration failed' or 'Text content did not match'
- !Page flickers on load
- !Components render differently on server vs client
- !Dynamic content causes warnings
Step-by-Step Fix
Identify the mismatch
The error message tells you which element differs. Look for dynamic content that changes between server and client renders.
Wrap browser APIs in useEffect
Code using window, document, localStorage must run only on the client. Use useEffect(() => { /* browser code */ }, []).
Use suppressHydrationWarning
For intentional differences (timestamps, user-specific content), add suppressHydrationWarning to the element.
Check for conditional rendering
If rendering differs based on authentication or user data, show a loading state on the server and the real content after hydration.
Avoid inline Date/Math.random
new Date().toLocaleString() and Math.random() produce different results on server vs client. Compute these in useEffect.
Frequently Asked Questions
Hydration is when React attaches event handlers to server-rendered HTML. If the HTML doesn't match what React expects, you get a hydration error.
Yes, for intentional mismatches (like timestamps). But don't use it to hide real bugs — fix the actual mismatch.
Related
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