---
id: wiki-2026-0508-soft-navigation
title: Soft Navigation
category: 10_Wiki/Topics
status: verified
canonical_id: self
aliases: [SPA Navigation, Client-side Routing, Soft Nav]
duplicate_of: none
source_trust_level: A
confidence_score: 0.9
verification_status: applied
tags: [web-performance, web-vitals, spa, navigation, history-api]
raw_sources: []
last_reinforced: 2026-05-10
github_commit: pending
tech_stack:
  language: JavaScript
  framework: React/Next.js/Remix
---

# Soft Navigation

## 매 한 줄
> **"매 page 의 reload 없이 매 URL + DOM 의 swap"**. Soft navigation 매 SPA pattern, History API (`pushState`) + view transitions 매 modern impl. 매 2025+ 의 Web Vitals 매 soft-nav LCP/INP 의 attribute (Soft Navigations API), 매 Chrome 138+ stable.

## 매 핵심

### 매 hard vs soft 의 line
- **Hard nav**: 매 full document load, 매 `unload`/`load`, fresh JS context.
- **Soft nav**: 매 client-side router. URL 매 `history.pushState`, DOM 매 partial swap. 매 same JS context.
- **CWV impact**: 매 v1 vitals 매 hard 만 measure. 매 2025 Soft Navigations API 매 soft 도 LCP/INP/CLS 의 attribute.

### 매 detection criteria (Chrome)
1. User-initiated (click, keypress).
2. URL change via History API.
3. DOM change (significant) post-event.
4. 매 셋 의 모두 conjunction → soft-nav event.

### 매 view transitions API
- **same-doc**: `document.startViewTransition(() => updateDOM())`. 매 2024 stable.
- **cross-doc** (MPA mode): 매 2025 Chrome 126+. `@view-transition { navigation: auto }`.
- 매 Web Animations API 의 wrap, 매 CSS `::view-transition-*` 의 customize.

### 매 응용
1. Next.js App Router (RSC streaming + soft nav).
2. Remix nested routes.
3. Astro view-transitions.
4. SvelteKit goto().

## 💻 패턴

### Native History API
```javascript
// router.js
class SoftRouter {
  constructor() {
    window.addEventListener('popstate', this.render.bind(this));
    document.addEventListener('click', this.intercept.bind(this));
  }

  intercept(e) {
    const a = e.target.closest('a[data-soft]');
    if (!a) return;
    e.preventDefault();
    this.navigate(a.href);
  }

  async navigate(url) {
    history.pushState({}, '', url);
    await this.render();
  }

  async render() {
    const path = location.pathname;
    if (document.startViewTransition) {
      document.startViewTransition(() => this.update(path));
    } else {
      this.update(path);
    }
  }

  update(path) {
    document.querySelector('main').innerHTML = renderRoute(path);
  }
}
new SoftRouter();
```

### Next.js 15 App Router
```tsx
// app/products/[id]/page.tsx
import { Suspense } from 'react';

export default async function Product({ params }) {
  const data = await fetch(`/api/p/${params.id}`).then(r => r.json());
  return (
    <Suspense fallback={<Skeleton />}>
      <ProductView data={data} />
    </Suspense>
  );
}

// link triggers soft nav by default
import Link from 'next/link';
<Link href="/products/42" prefetch>View</Link>
```

### Cross-doc view transition (Astro / vanilla)
```html
<!-- src/layouts/Base.astro -->
<head>
  <style>
    @view-transition { navigation: auto; }
    ::view-transition-old(root) { animation: fade-out 0.2s; }
    ::view-transition-new(root) { animation: fade-in 0.2s; }
  </style>
</head>
```

### Soft Navigations API (measurement)
```javascript
// observer.js
new PerformanceObserver(list => {
  for (const entry of list.getEntries()) {
    console.log('soft nav', {
      from: entry.url,
      startTime: entry.startTime,
      navigationId: entry.navigationId,
    });
  }
}).observe({ type: 'soft-navigation', buffered: true });

// Attribute LCP per soft-nav
new PerformanceObserver(list => {
  for (const e of list.getEntries()) {
    if (e.navigationId !== 'auto') {
      console.log('soft LCP', e.startTime, e.element);
    }
  }
}).observe({ type: 'largest-contentful-paint', buffered: true });
```

### Prefetch on hover/intent
```javascript
document.addEventListener('mouseover', e => {
  const a = e.target.closest('a[data-soft]');
  if (a && !a.dataset.prefetched) {
    fetch(a.href, { priority: 'low' });
    a.dataset.prefetched = '1';
  }
});
```

### web-vitals attribution (soft nav)
```javascript
import { onLCP, onINP, onCLS } from 'web-vitals/attribution';

onLCP(metric => sendBeacon('/v', { ...metric, navType: metric.navigationType }), {
  reportSoftNavs: true,
});
onINP(m => sendBeacon('/v', m), { reportSoftNavs: true });
```

## 매 결정 기준
| 상황 | Approach |
|---|---|
| Static-mostly site | 매 MPA + cross-doc view transition |
| Heavy interactivity | 매 SPA soft nav (Next.js / Remix) |
| Mixed | 매 islands (Astro) + selective soft nav |
| Performance-critical | 매 prefetch on intent + Suspense streaming |

**기본값**: 매 framework 의 router (Next.js / Remix / SvelteKit) 의 use; 매 view transitions 의 progressive-enhance.

## 🔗 Graph
- 부모: [[SPA]] · [[Web-Performance]]
- 변형: [[Turbo]] · [[HTMX]]
- 응용: [[View-Transitions-API]] · [[Web-Vitals]]
- Adjacent: [[INP]] · [[LCP]] · [[Streaming SSR]]

## 🤖 LLM 활용
**언제**: 매 router code scaffolding, 매 RUM analytics dashboard query gen, 매 view-transition CSS draft.
**언제 X**: 매 perf measurement (real RUM data needed), 매 a11y validation (manual + axe).

## ❌ 안티패턴
- **No focus management**: 매 soft nav 후 focus 매 lost. 매 a11y violation. `route.focus()` on `<main>`.
- **No scroll restoration**: 매 back-button 매 wrong scroll. `history.scrollRestoration='manual'` + manual restore.
- **CLS spike**: 매 layout shift 의 unmeasured. 매 view-transitions 의 use.
- **Blocking JS during nav**: 매 INP 매 800ms+. 매 Suspense / streaming.
- **No prefetch budget**: 매 hover 매 모든 link 의 fetch — 매 bandwidth waste.

## 🧪 검증 / 중복
- Verified (web.dev Soft Navigations 2025; Chrome Status #5085744967254016; web-vitals.js v4 docs).
- 신뢰도 A.

## 🕓 Changelog
| 날짜 | 변경 |
|---|---|
| 2026-05-08 | Phase 1 |
| 2026-05-10 | Manual cleanup — full content (History API + view transitions + Soft Nav API patterns) |
