frontend-fundamentals

name	frontend-fundamentals
description	Auto-invoke when reviewing React, Vue, or frontend component code. Enforces component architecture, state management patterns, and UI best practices.

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

❌ 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

❌ 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

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

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

4. Boolean Prop Soup

❌ <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

Flag	Question to Ask
File > 200 lines	"Can we split this into smaller pieces?"
> 5 useState calls	"Should some of this state be lifted or combined?"
useEffect with [] deps but uses external values	"Are we missing dependencies?"
Direct DOM manipulation	"Is there a React way to do this?"
Inline styles everywhere	"Should we use a consistent styling approach?"