2nd/10_Wiki/Topics/Frontend/Frontend.md

---
id: wiki-2026-0508-frontend
title: Frontend
category: 10_Wiki/Topics
status: verified
canonical_id: self
aliases: [Web Frontend, Client-side Engineering, UI Engineering]
duplicate_of: none
source_trust_level: A
confidence_score: 0.9
verification_status: applied
tags: [frontend, web, react, performance]
raw_sources: []
last_reinforced: 2026-05-10
github_commit: pending
tech_stack:
  language: typescript
  framework: react
---

# Frontend

## 매 한 줄
> **"매 user 의 매 device 에서 매 실행되는 매 모든 것 — 매 markup, 매 style, 매 behavior, 매 network."**. 2026 의 매 frontend 는 매 React 19 + 매 RSC + 매 Vite/Turbopack + 매 Bun/Node + 매 Edge runtime 의 매 stack 에서 매 진화 중. Core Web Vitals + 매 a11y + 매 i18n 이 매 hygiene.

## 매 핵심

### 매 Layer
- **Markup**: HTML, semantic, a11y.
- **Style**: CSS — Cascade Layers, Container Queries, `:has()`, OKLCH.
- **Behavior**: JS/TS — framework (React/Vue/Svelte/Solid).
- **Build**: Vite, Turbopack, Bun, esbuild, swc.
- **Runtime**: Browser, Edge (Cloudflare Workers, Vercel), Node, Bun.

### 매 Framework landscape (2026)
- **React 19**: RSC + Actions + use() hook + Compiler.
- **Next.js 15**: App Router default, Turbopack stable.
- **Astro 5**: content site / island.
- **SvelteKit 2** / **Vue 3.5 + Nuxt 4** / **Solid 2**.
- **Remix → React Router 7**: data loading first.

### 매 Performance pillars
- **LCP < 2.5s**: image optimize, preconnect, fetchpriority.
- **INP < 200ms**: long task chunking, scheduler.yield.
- **CLS < 0.1**: dimension reserved, font-display swap.
- **Bundle**: route split, tree-shake, dynamic import.

### 매 Modern primitives
- **CSS**: container queries, `:has()`, view transitions API, anchor positioning.
- **JS**: scheduler.yield, AbortSignal.timeout, Temporal (stage 4 2026).
- **HTML**: popover, dialog, search.
- **Network**: HTTP/3, Early Hints, Speculation Rules.

### 매 응용
1. SSR + RSC 로 매 SEO 기반 commerce.
2. Edge personalization — 매 cookie / geo 기반.
3. PWA + offline-first.

## 💻 패턴

### View Transitions API (cross-document)
```html
<meta name="view-transition" content="same-origin" />
<style>
  ::view-transition-old(hero) { animation: fade-out 0.3s; }
  ::view-transition-new(hero) { animation: fade-in 0.3s; }
  .hero { view-transition-name: hero; }
</style>
```

### Container query
```css
.card { container-type: inline-size; }
@container (min-width: 400px) {
  .card-body { display: grid; grid-template-columns: 1fr 1fr; }
}
```

### React 19 Actions (form)
```tsx
'use client';
async function submit(formData: FormData) {
  'use server';
  await db.insert(formData.get('msg') as string);
}
export default function Form() {
  return <form action={submit}><input name="msg" /><button>Send</button></form>;
}
```

### use() hook (React 19)
```tsx
function Comments({ promise }: { promise: Promise<Comment[]> }) {
  const comments = use(promise);   // suspends
  return <ul>{comments.map(c => <li key={c.id}>{c.text}</li>)}</ul>;
}
```

### Image optimization (Next 15)
```tsx
import Image from 'next/image';
<Image src="/hero.avif" width={1280} height={720} priority alt="" sizes="100vw" />
```

### Speculation Rules (prerender)
```html
<script type="speculationrules">
{
  "prerender": [{ "where": { "selector_matches": "a.product" }, "eagerness": "moderate" }]
}
</script>
```

### Scheduler.yield long task
```javascript
async function process(items) {
  for (const it of items) {
    work(it);
    if ('scheduler' in self) await scheduler.yield();
  }
}
```

### CSS cascade layers
```css
@layer reset, base, components, utilities;
@layer reset { * { margin: 0; box-sizing: border-box; } }
@layer components { .btn { padding: 0.5rem 1rem; } }
```

## 매 결정 기준
| 상황 | Stack |
|---|---|
| 매 SEO content site | Astro 5 (zero JS default) |
| 매 SaaS dashboard | Vite + React 19 (CSR) |
| 매 commerce | Next 15 App Router (RSC + ISR) |
| 매 docs | Astro Starlight / Docusaurus |
| 매 marketing | Astro / 11ty |
| 매 realtime | React + WebSocket / Liveblocks |

**기본값**: Vite + React 19 + TS strict + ESLint + Vitest. 매 SSR 필요 시 매 Next 15.

## 🔗 Graph
- 응용: [[E-commerce]]
- Adjacent: [[React]] · [[Performance]] · [[Accessibility (A11y)|Accessibility]]

## 🤖 LLM 활용
**언제**: 매 stack 선택, 매 perf 진단, 매 pattern (RSC, Suspense, View Transitions) 적용.
**언제 X**: 매 backend-only — 매 다른 도메인.

## ❌ 안티패턴
- **CSS-in-JS runtime**: 매 INP 악화 (2026 모범: zero-runtime — Tailwind / vanilla-extract / Panda).
- **Mega global state**: 매 server vs client state 미분리.
- **Polyfill 남발**: 매 modern browser default — 매 baseline 활용.
- **No a11y test**: 매 axe-core CI 없음.

## 🧪 검증 / 중복
- Verified (web.dev, MDN baseline 2026, React 19 docs).
- 신뢰도 A.

## 🕓 Changelog
| 날짜 | 변경 |
|---|---|
| 2026-05-08 | Phase 1 |
| 2026-05-10 | Manual cleanup — 매 2026 stack + modern primitives |