admin
87 lines
1.7 KiB
Markdown
87 lines
1.7 KiB
Markdown
# Hydration Errors
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Diagnose and fix React hydration mismatch errors.
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## Error Signs
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- "Hydration failed because the initial UI does not match"
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- "Text content does not match server-rendered HTML"
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## Debugging
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In development, click the hydration error to see the server/client diff.
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## Common Causes and Fixes
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### Browser-only APIs
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```tsx
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// Bad: Causes mismatch - window doesn't exist on server
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<div>{window.innerWidth}</div>;
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// Good: Use client component with mounted check
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('use client');
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import { useState, useEffect } from 'react';
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export function ClientOnly({ children }: { children: React.ReactNode }) {
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const [mounted, setMounted] = useState(false);
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useEffect(() => setMounted(true), []);
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return mounted ? children : null;
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}
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```
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### Date/Time Rendering
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Server and client may be in different timezones:
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```tsx
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// Bad: Causes mismatch
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<span>{new Date().toLocaleString()}</span>;
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// Good: Render on client only
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('use client');
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const [time, setTime] = useState<string>();
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useEffect(() => setTime(new Date().toLocaleString()), []);
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```
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### Random Values or IDs
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```tsx
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// Bad: Random values differ between server and client
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<div id={Math.random().toString()}>
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// Good: Use useId hook
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import { useId } from 'react'
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function Input() {
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const id = useId()
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return <input id={id} />
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}
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```
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### Invalid HTML Nesting
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```tsx
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// Bad: Invalid - div inside p
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<p><div>Content</div></p>
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// Bad: Invalid - p inside p
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<p><p>Nested</p></p>
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// Good: Valid nesting
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<div><p>Content</p></div>
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```
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### Third-party Scripts
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Scripts that modify DOM during hydration.
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```tsx
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// Good: Use next/script with afterInteractive
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import Script from 'next/script';
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export default function Page() {
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return <Script src="https://example.com/script.js" strategy="afterInteractive" />;
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}
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```
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