Agent skill
frontend-dev-guidelines
Frontend development guidelines for React/TypeScript applications. Modern patterns including Suspense, lazy loading, useSWR, file organization with features directory, shadcn/ui components, Tailwind CSS styling, Next.js App Router, performance optimization, and TypeScript best practices. Use when creating components, pages, features, fetching data, styling, routing, or working with frontend code.
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SKILL.md
Frontend Dev Guidelines (Senior Level)
This skill is at senior frontend developer knowledge level. Memorize patterns, recognize edge cases, reject anti-patterns.
1. Senior Developer Mindset
Think performance-first:
- Ask "is this causing unnecessary renders?" for every component
- Detect network waterfalls, use parallel fetch
- Monitor bundle size, lazy load heavy components
Internalize patterns:
React.FC<Props>+ TypeScript alwaysuseSWRwithsuspense: trueis standardSuspenseLoaderNEVER early return with spinner
Reject anti-patterns:
- Convert barrel file imports to direct imports
- Replace sequential await with
Promise.all() - Replace hardcoded colors with globals.css variables
2. Non-Negotiables (CRITICAL)
Component Patterns
// ✅ STANDARD PATTERN
import React from 'react';
import useSWR from 'swr';
import { SuspenseLoader } from '@/shared/components/SuspenseLoader';
const HeavyComponent = React.lazy(() => import('./HeavyComponent'));
interface MyComponentProps {
id: string;
className?: string;
}
export const MyComponent: React.FC<MyComponentProps> = ({ id, className }) => {
const { data } = useSWR(`key-${id}`, () => api.get(id), { suspense: true });
return <div className={cn("base-class", className)}>{data?.title}</div>;
};
// Usage - with Suspense boundary
<SuspenseLoader>
<MyComponent id="123" />
</SuspenseLoader>
Performance Rules (Top 15)
| Priority | Rule | Description |
|---|---|---|
| CRITICAL | Promise.all() |
Parallelize independent async operations |
| CRITICAL | Direct imports | Avoid barrel files, import directly |
| CRITICAL | next/dynamic |
Dynamic import heavy components |
| CRITICAL | Suspense boundaries | Stream content, prevent waterfalls |
| HIGH | Defer await | Move await to the branch where it's used |
| HIGH | Minimize RSC serialization | Send less data to client |
| HIGH | React.cache() |
Per-request deduplication |
| MEDIUM | SWR deduplication | Auto request deduplication |
| MEDIUM | Functional setState | setCount(c => c + 1) stable callback |
| MEDIUM | Lazy state init | useState(() => expensiveCalc()) |
| MEDIUM | startTransition |
For non-urgent updates |
| MEDIUM | content-visibility |
CSS optimize for long lists |
| LOW | Index maps | Use Map for repeated lookups |
| LOW | toSorted() |
For immutable sort |
| LOW | Set/Map lookups | O(1) lookup instead of array |
Accessibility Rules (Top 10)
| Rule | Description |
|---|---|
aria-label on icon buttons |
ALWAYS add aria-label to icon-only buttons |
button vs a/Link |
Action = button, Navigation = a/Link |
alt on images |
Add alt to every img (decorative: alt="") |
| Keyboard handlers | Add keyboard support to interactive elements |
| Heading hierarchy | Maintain h1 → h2 → h3 order |
autocomplete on inputs |
Add autocomplete to form inputs |
| Inline errors | Show errors next to field |
| Submit button enabled | Don't disable submit, show loading spinner |
| Virtualize long lists | Virtualize lists with 50+ items |
prefers-reduced-motion |
Check motion preference in animations |
3. Browser Compatibility (SAFARI CRITICAL)
Check Safari on every code change! Safari is the most problematic browser.
| Issue | Safari Fix | Reference |
|---|---|---|
new Date('2024-01-15 10:30:00') |
ISO 8601: '2024-01-15T10:30:00' |
browser-compatibility.md |
height: 100vh |
height: 100dvh or -webkit-fill-available |
browser-compatibility.md |
backdrop-filter |
Add -webkit-backdrop-filter prefix |
browser-compatibility.md |
| Video autoplay | playsInline + muted attributes |
browser-compatibility.md |
| Input zoom (iOS) | font-size: 16px minimum |
browser-compatibility.md |
| Touch events | { passive: true } listener |
browser-compatibility.md |
| Clipboard API | Fallback textarea method | browser-compatibility.md |
Test Checklist (Every PR):
- Chrome (latest)
- Safari (macOS)
- Safari (iOS) - Real device or simulator
- Firefox (latest)
4. Anti-Patterns (NEVER DO)
| Anti-Pattern | Correct Pattern | Reference |
|---|---|---|
if (isLoading) return <Spinner /> |
Wrap with <SuspenseLoader> |
core-patterns.md |
| Sequential await | Use Promise.all() |
performance-guide.md |
| Barrel file import | Use direct import | performance-guide.md |
Hardcoded color bg-[#fe4601] |
CSS variable bg-orange-1 |
styling-routing.md |
<div onClick> |
<button onClick> |
accessibility-guide.md |
| Icon button without label | Add aria-label |
accessibility-guide.md |
| Server data in useState | Use useSWR |
core-patterns.md |
next/router import |
Use next/navigation |
styling-routing.md |
dangerouslySetInnerHTML |
DOMPurify sanitization | security-error-handling.md |
any type |
unknown + type guard |
advanced-typescript.md |
Type assertion as User |
Runtime validation (Zod) | advanced-typescript.md |
5. Decision Trees
useState vs Zustand vs SWR
What's the data source?
├─ Server/API → SWR (suspense: true)
├─ Form input → useState (local)
├─ UI state (modal, sidebar) → useState (local)
└─ Shared across components?
├─ Server data → SWR (auto-shares)
└─ Client state → Zustand (ONLY)
Server vs Client Component
What does the component do?
├─ Static content → Server Component
├─ Data fetch (no interaction) → Server Component
├─ Needs useState/useEffect → Client Component
├─ Has onClick/onChange handler → Client Component
├─ Uses Browser API → Client Component
└─ Third-party client library → Client Component
useMemo vs React.memo vs useCallback
What are you optimizing?
├─ Expensive calculation → useMemo
├─ Object/array reference stability → useMemo
├─ Function reference stability → useCallback
├─ Child component re-render → React.memo (on child)
└─ Event handler in dependency → useCallback
Lazy Loading Decision
Is the component heavy?
├─ DataGrid/Table → lazy load
├─ Chart/Graph → lazy load
├─ Rich text editor → lazy load
├─ Video player → lazy load
├─ Small utility component → don't lazy load
└─ Above-the-fold critical → don't lazy load
6. Quick Reference
For detailed info: styling-routing.md
| Topic | Source |
|---|---|
Import aliases (@/, @/shared, @/features) |
styling-routing.md |
| Feature directory structure | styling-routing.md |
Route groups ((dashboard), (main), etc.) |
styling-routing.md |
| Color palettes (globals.css) | styling-routing.md |
7. Resources (Detailed Info)
| Topic | Resource |
|---|---|
| Component, data fetching, React 19 hooks, state | core-patterns.md |
| All performance rules (45 rules) | performance-guide.md |
| Accessibility patterns (WCAG 2.1) | accessibility-guide.md |
| Tailwind, routing, file organization | styling-routing.md |
| Testing patterns, complete examples | testing-examples.md |
| Safari/Chrome/Firefox compatibility, Senior FE skills | browser-compatibility.md |
| XSS/CSRF prevention, error boundaries, resilience | security-error-handling.md |
| Generics, type guards, utility types, inference | advanced-typescript.md |
Quick Template
import React from 'react';
import useSWR from 'swr';
import { Card, CardHeader, CardTitle, CardContent } from '@/shared/components/ui/card';
import { cn } from '@/shared/utils/cn';
import { featureApi } from '../api/featureApi';
interface FeatureCardProps {
id: string;
className?: string;
}
export const FeatureCard: React.FC<FeatureCardProps> = ({ id, className }) => {
const { data } = useSWR(`feature-${id}`, () => featureApi.get(id), { suspense: true });
return (
<Card className={cn("w-full", className)}>
<CardHeader>
<CardTitle>{data?.title}</CardTitle>
</CardHeader>
<CardContent>
<p className="text-muted-foreground">{data?.description}</p>
</CardContent>
</Card>
);
};
Related Skills
- react-best-practices: Full 45 performance rules (Vercel Engineering)
- web-design-guidelines: Full UI/UX/a11y rules (Vercel Labs)
- error-tracking: Sentry integration
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