Udit TakkarandGitHub
7a9fdd5a0c
## What does this PR do? This PR adds https://vercel.com/blog/introducing-react-best-practices for your coding agent using `npx add-skill vercel-labs/agent-skills` command The skills are added to `.claude/`, `.cursor/`, and `.opencode/` directories to provide React and Next.js performance optimization guidance for AI-assisted workflows. ## Updates since last revision Addressed Cubic AI review feedback for issues with confidence >= 9/10: - **rerender-dependencies.md** - Replaced `console.log(user.id)` with `fetchUserDetails(user.id)` to avoid logging sensitive information - **server-after-nonblocking.md** - Removed `sessionCookie` from `logUserAction` call to avoid logging sensitive authentication data, added `await` to async call - **bundle-conditional.md** - Added `loadError` state and `setLoadError` setter to fix undefined `setEnabled` reference - **advanced-event-handler-refs.md** - Updated `useWindowEvent` handler signature to accept `Event` parameter and forward it to the stored handler - **rerender-derived-state.md** - Closed `<nav>` elements in both examples for valid JSX Fixes applied to both `.claude` and `.cursor` skill directories for consistency. ## Mandatory Tasks (DO NOT REMOVE) - [x] I have self-reviewed the code (A decent size PR without self-review might be rejected). - [x] N/A I have updated the developer docs in /docs if this PR makes changes that would require a [documentation change](https://cal.com/docs). If N/A, write N/A here and check the checkbox. - [x] N/A, I confirm automated tests are in place that prove my fix is effective or that my feature works. ## How should this be tested? These are documentation files for AI coding agents. No runtime testing required - review the markdown files to verify the example code snippets are correct. ## Checklist for human review - [ ] Verify example code snippets in the skill files are syntactically correct - [ ] Confirm the fixes don't introduce new issues in the documentation examples - [ ] Check that `.claude` and `.cursor` directories have consistent content --- Link to Devin run: https://app.devin.ai/sessions/f7f7e67fdeea4b22a4817d63ed9e1759 Requested by: unknown ()
83 lines
2.3 KiB
Markdown
83 lines
2.3 KiB
Markdown
---
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title: Prevent Hydration Mismatch Without Flickering
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impact: MEDIUM
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impactDescription: avoids visual flicker and hydration errors
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tags: rendering, ssr, hydration, localStorage, flicker
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---
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## Prevent Hydration Mismatch Without Flickering
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When rendering content that depends on client-side storage (localStorage, cookies), avoid both SSR breakage and post-hydration flickering by injecting a synchronous script that updates the DOM before React hydrates.
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**Incorrect (breaks SSR):**
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```tsx
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function ThemeWrapper({ children }: { children: ReactNode }) {
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// localStorage is not available on server - throws error
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const theme = localStorage.getItem('theme') || 'light'
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return (
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<div className={theme}>
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{children}
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</div>
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)
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}
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```
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Server-side rendering will fail because `localStorage` is undefined.
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**Incorrect (visual flickering):**
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```tsx
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function ThemeWrapper({ children }: { children: ReactNode }) {
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const [theme, setTheme] = useState('light')
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useEffect(() => {
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// Runs after hydration - causes visible flash
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const stored = localStorage.getItem('theme')
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if (stored) {
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setTheme(stored)
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}
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}, [])
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return (
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<div className={theme}>
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{children}
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</div>
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)
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}
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```
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Component first renders with default value (`light`), then updates after hydration, causing a visible flash of incorrect content.
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**Correct (no flicker, no hydration mismatch):**
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```tsx
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function ThemeWrapper({ children }: { children: ReactNode }) {
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return (
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<>
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<div id="theme-wrapper">
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{children}
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</div>
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<script
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dangerouslySetInnerHTML={{
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__html: `
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(function() {
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try {
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var theme = localStorage.getItem('theme') || 'light';
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var el = document.getElementById('theme-wrapper');
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if (el) el.className = theme;
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} catch (e) {}
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})();
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`,
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}}
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/>
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</>
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)
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}
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```
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The inline script executes synchronously before showing the element, ensuring the DOM already has the correct value. No flickering, no hydration mismatch.
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This pattern is especially useful for theme toggles, user preferences, authentication states, and any client-only data that should render immediately without flashing default values.
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