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

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?

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" />

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?"

Standards Reference

See detailed patterns in:

• •/standards/frontend/component-architecture.md

Red Flags to Call Out