/frontend

name: frontend-fundamentals
description: Reviews React/Vue component architecture, state, and hooks. Use when junior builds components, forms, modals, uses useState, useEffect, adds state, or asks "is this good React".

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?" |