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name: frontend-fundamentals description: | TRIGGERS: "review my component", "is this good React?", "check my UI", "component review", "building component", "creating UI", "adding React", "implementing hook", "rendering", "making a form", "building a page", "creating modal", "adding state", "useEffect", React, Vue, components, state management, hooks, props, rendering, JSX, CSS, Tailwind. USE WHEN: Junior is BUILDING UI components, managing state, handling events, or structuring frontend code. PROVIDES: Component architecture, state patterns, hooks best practices, rendering optimization. PROACTIVE: Triggers when junior mentions building frontend features, not just reviewing.

Frontend Fundamentals Review

"A component should do ONE thing well. If you're describing it with 'and', split it."

When to Apply

Activate this skill when reviewing:

• React/Vue/Svelte components
• UI rendering logic
• State management code
• CSS/styling decisions
• Client-side routing

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Review Checklist

Component Architecture

• Single Responsibility: Does each component do ONE job?
• Size Check: Is the component under 200 lines?
• Props Count: Are there fewer than 7 props?
• Naming: Can you describe the component without saying "and"?

State Management

• Colocation: Is state as close as possible to where it's used?
• Lifting: Is state shared properly between siblings via parent?
• Context vs Props: Is prop drilling avoided (max 3 levels)?
• Server State: Is server data managed separately (React Query/SWR)?

Performance

• Memoization: Are expensive computations wrapped in useMemo?
• Callbacks: Are event handlers wrapped in useCallback where needed?
• Re-renders: Will this cause unnecessary re-renders?
• Lazy Loading: Are heavy components code-split?

Accessibility

• Semantic HTML: Are proper elements used (button vs div)?
• ARIA: Are interactive elements accessible?
• Keyboard: Can users navigate without a mouse?

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Common Mistakes (Anti-Patterns)

1. God Components

Copy❌ UserDashboard.tsx (1000 lines)
   - fetches data, manages state, renders UI, handles routing

✅ Split into:
   - UserDashboardPage.tsx (container)
   - UserStats.tsx (presentation)
   - UserActivity.tsx (presentation)
   - useUserData.ts (hook)

2. Logic in Render

Copy❌ return <div>{users.filter(u => u.active).map(u => ...)}</div>

✅ const activeUsers = useMemo(() => users.filter(u => u.active), [users]);
   return <div>{activeUsers.map(u => ...)}</div>

3. Prop Drilling

Copy❌ <App user={user}>
     <Layout user={user}>
       <Main user={user}>
         <Widget user={user} />

✅ const user = useUser(); // in Widget.tsx

4. Boolean Prop Soup

Copy❌ <Button primary secondary large small disabled loading />

✅ <Button variant="primary" size="large" state="loading" />

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Socratic Questions

Ask the junior these questions instead of giving answers:

1. Architecture: "What is the ONE job of this component?"
2. Splitting: "If I asked you to use just the header part elsewhere, could you?"
3. State: "Who needs this data? Should it live here or higher up?"
4. Performance: "What happens when the parent re-renders?"
5. Complexity: "Could a new developer understand this in 5 minutes?"

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Standards Reference

See detailed patterns in:

• /standards/frontend/component-architecture.md

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Red Flags to Call Out