2nd/10_Wiki/Topics/AI_and_ML/DOM vs Virtual DOM.md

---
id: wiki-2026-0508-dom-vs-virtual-dom
title: DOM vs Virtual DOM
category: 10_Wiki/Topics
status: verified
canonical_id: self
aliases: [DOM, Virtual DOM, vDOM, reconciliation, diffing, React fiber, Solid signals, Svelte compile]
duplicate_of: none
source_trust_level: A
confidence_score: 0.93
verification_status: applied
tags: [frontend, dom, virtual-dom, react, fiber, solid, svelte, signals, fine-grained-reactivity]
raw_sources: []
last_reinforced: 2026-05-10
github_commit: pending
tech_stack:
  language: JavaScript / React / Solid / Svelte
  framework: React / Solid / Svelte / Vue
---

# DOM vs Virtual DOM

## 매 한 줄
> **"매 DOM mutation 의 expensive — 매 abstraction 의 batch"**. React 의 Virtual DOM (2013). 매 modern: 매 fine-grained reactivity (Solid, Svelte, Vue 3) 의 vDOM 의 supersede 의 trend. 매 pure DOM (vanilla, htmx) 의 revival.

## 매 핵심

### Real DOM
- 매 browser 의 tree.
- 매 mutation 의 reflow / repaint 의 trigger.
- 매 manual update 의 error-prone.

### Virtual DOM (React)
- 매 lightweight JS object 의 in-memory.
- 매 declarative state.
- 매 diff + 매 reconciliation 의 minimal real DOM update.

### 매 React 의 algorithm
1. 매 새 Virtual DOM tree.
2. 매 diff vs 매 previous (heuristic O(n)).
3. 매 minimal real DOM mutation.

### 매 React 의 heuristic
- **Different type** → 매 entirely new tree.
- **`key` attribute** → 매 stable child identity.
- **Component type same + props different** → 매 update only changed.

### 매 modern alternative

#### Fine-grained reactivity (Solid, Svelte 5, Vue 3)
- 매 vDOM 의 X.
- 매 signal / effect 의 specific DOM 의 update.
- 매 faster + smaller bundle.

#### Compile-time (Svelte)
- 매 framework 의 compile away.
- 매 매 component 의 specific imperative code.

#### htmx / Pure HTML
- 매 server-side render + 매 partial swap.
- 매 매 minimum JS.

### 매 trade-off
| 측면 | Real DOM | Virtual DOM | Fine-grained |
|---|---|---|---|
| Direct manipulation | Manual | Abstracted | Abstracted |
| Update granularity | Per-mutation | Per-component | Per-signal |
| Memory | Low | Medium | Low |
| Bundle size | Tiny | 50KB+ (React) | <10KB (Solid) |
| Rendering speed | Variable | Good | Best |
| Mental model | Imperative | Declarative + render fn | Declarative + signals |

### 매 React Fiber (2017)
- 매 reconciliation 의 interruptible.
- 매 priority-based.
- 매 concurrent rendering.
- 매 React 18+ default.

### 매 modern React 18+ optimization
- **Concurrent rendering**: 매 interrupt.
- **Automatic batching**.
- **Suspense + streaming**.
- **`useTransition` / `useDeferredValue`**.
- **RSC** (Server Components).

### 매 응용
1. **Large dynamic UI**: React / Solid.
2. **Static + light interactivity**: htmx / Astro islands.
3. **Form-heavy**: Solid (fast).
4. **SEO-critical**: Next.js (SSR).
5. **Data viz**: D3 + minimal framework.

## 💻 패턴

### React (declarative)
```jsx
function Counter() {
  const [count, setCount] = useState(0);
  return (
    <button onClick={() => setCount(count + 1)}>
      Count: {count}
    </button>
  );
}
// React 가 매 setCount 시 의 새 vDOM → diff → 매 button text 만 update.
```

### `key` for stable identity
```jsx
function List({ items }) {
  return (
    <ul>
      {items.map(item => (
        <li key={item.id}>{item.name}</li>  // 매 key 의 stable identity
      ))}
    </ul>
  );
}
```

### `useMemo` / `React.memo`
```jsx
const ExpensiveItem = React.memo(({ item, onClick }) => (
  <div onClick={onClick}>{item.name}</div>
));

function List({ items, onSelect }) {
  // 매 stable callback for memoization
  const handleSelect = useCallback((id) => onSelect(id), [onSelect]);
  
  const sorted = useMemo(() => 
    items.sort((a, b) => a.priority - b.priority), [items]);
  
  return sorted.map(item => 
    <ExpensiveItem key={item.id} item={item} onClick={handleSelect} />
  );
}
```

### Solid (signals, no vDOM)
```jsx
import { createSignal } from 'solid-js';

function Counter() {
  const [count, setCount] = createSignal(0);
  return (
    <button onClick={() => setCount(count() + 1)}>
      Count: {count()}
    </button>
  );
}
// 매 specific text node 의 update — 매 component re-render X.
```

### Svelte (compile-time)
```svelte
<script>
  let count = 0;
</script>

<button on:click={() => count++}>
  Count: {count}
</button>

<!-- 매 compile 의 imperative code 의 generate -->
```

### Vue 3 (Proxy-based reactivity + vDOM)
```vue
<script setup>
import { ref } from 'vue';
const count = ref(0);
</script>

<template>
  <button @click="count++">Count: {{ count }}</button>
</template>
```

### htmx (no JS framework)
```html
<button hx-post="/click" hx-target="#count" hx-swap="innerHTML">
  Click me
</button>
<span id="count">0</span>

<!-- 매 server 가 매 HTML 의 return → 매 swap -->
```

### Direct DOM (vanilla)
```js
const button = document.querySelector('button');
let count = 0;
button.addEventListener('click', () => {
  count++;
  button.textContent = `Count: ${count}`;  // 매 direct mutation
});
```

### Concurrent rendering (React 18+)
```jsx
import { useTransition, useDeferredValue } from 'react';

function SearchableList({ items }) {
  const [filter, setFilter] = useState('');
  const deferred = useDeferredValue(filter);
  
  const filtered = items.filter(i => i.name.includes(deferred));
  
  return (
    <>
      <input value={filter} onChange={e => setFilter(e.target.value)} />
      <List items={filtered} />
    </>
  );
}
```

### Performance comparison (React vs Solid)
```ts
// 매 typical bench:
// React useState + setCount: 매 10K updates → 매 500ms
// Solid signal + setCount: 매 10K updates → 매 50ms (10×)
```

### `<picture>` and DOM (no framework)
```html
<picture>
  <source srcset="/img.avif" type="image/avif">
  <img src="/img.jpg" alt="..." width="800" height="600">
</picture>
<!-- 매 HTML primitive 의 사용 -->
```

## 매 결정 기준
| 상황 | Approach |
|---|---|
| Large dynamic SPA | React + Concurrent |
| Performance-critical | Solid / Svelte |
| SEO + static + light JS | Astro + Islands |
| Form-heavy | Solid |
| Server-driven | htmx + HTML |
| Data viz | D3 + minimal |
| Vanilla / lib-free | Direct DOM |

**기본값**: React for ecosystem. Solid / Svelte for performance.

## 🔗 Graph
- 부모: [[Frontend]] · [[Web-Performance]] · [[React]]
- 변형: [[Virtual DOM]] · [[Fine-Grained-Reactivity]]
- 응용: [[React]] · [[Solid]] · [[Vue-3]] · [[htmx]] · [[Astro]]
- Adjacent: [[Critical_Rendering_Path]] · [[CSS Animations]] · [[Core Web Vitals Optimization (INP, LCP 개선)]] · [[Container_Queries]]

## 🤖 LLM 활용
**언제**: 매 framework selection. 매 perf optimization. 매 bundle size 의 reduce.
**언제 X**: 매 backend (다른 paradigm).

## ❌ 안티패턴
- **Direct DOM mutation in React**: 매 desync.
- **`key={index}` for dynamic list**: 매 wrong reconciliation.
- **No memoization (heavy re-render)**: 매 perf.
- **Premature memoization**: 매 over-engineering.
- **vDOM 의 large overhead** (small list): 매 vanilla 의 더 빠름.

## 🧪 검증 / 중복
- Verified (React docs, Solid docs, Svelte performance benchmark).
- 신뢰도 A.
- Related: [[Critical_Rendering_Path]] · [[CSS Animations]] · [[Core Web Vitals Optimization (INP, LCP 개선)]] · [[Container_Queries]] · [[Case-Study-Allbirds-PWA-Redesign]].

## 🕓 Changelog
| 날짜 | 변경 |
|---|---|
| 2026-05-08 | Phase 1 |
| 2026-05-10 | Manual cleanup — DOM vs vDOM vs fine-grained + 매 React / Solid / Svelte / htmx code |