Next.js & React · Developer Error Resolution Lab

How to Fix 'Hydration failed because the initial UI does not match' in Next.js

Resolve Next.js React hydration mismatch errors caused by browser-only APIs (window, localStorage), timestamps, or invalid HTML nesting.

Fix Guide:

Triggered Error Message:

Error: Hydration failed because the initial UI does not match what was rendered on the server.

Customize Solution for Your Environment

Component Name

Browser API / Property

"use client";
import { useState, useEffect } from "react";

export function ClientComponent() {
  const [value, setValue] = useState<string | null>(null);
  const [mounted, setMounted] = useState(false);

  useEffect(() => {
    setMounted(true);
    try {
      setValue(localStorage.getItem('user'));
    } catch (e) {
      console.warn("Storage access restricted:", e);
    }
  }, []);

  if (!mounted) {
    // Render matching fallback on server & initial hydration pass
    return <div className="skeleton-loader animate-pulse" />;
  }

  return <div>Loaded value: {value}</div>;
}

Root Cause & Mechanism Analysis

Why does this error occur?

The server renders HTML with one state (e.g., server timestamp or no window object), but the client immediately renders different HTML upon hydration (e.g. `Date.now()`, `window.innerWidth`, or `typeof window !== 'undefined'`). Also triggered by invalid HTML like placing a `<p>` inside another `<p>` or `<div>` inside `<p>`.

Frequently Asked Questions

Can I use suppressHydrationWarning?

Yes, for text elements where differences are benign (such as dynamic dates or localized timestamps), adding `suppressHydrationWarning` to the element silences the error.

Why does invalid HTML nesting trigger hydration failure?

The browser's native HTML parser will auto-close or reposition invalid tags (like `<p><div></div></p>`), causing React's virtual DOM reconciliation to mismatch the browser DOM.

Browse All 35 Guides

Next.js & React