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

---
id: wiki-2026-0508-pinia
title: Pinia
category: 10_Wiki/Topics
status: verified
canonical_id: self
aliases: [Vue Store, Pinia Store]
duplicate_of: none
source_trust_level: A
confidence_score: 0.9
verification_status: applied
tags: [vue, state-management, frontend]
raw_sources: []
last_reinforced: 2026-05-10
github_commit: pending
tech_stack:
  language: TypeScript
  framework: Vue 3 / Pinia 2
---

# Pinia

## 매 한 줄
> **"매 Vue 3 매 official state management — 매 Vuex 4 후속, 매 Composition API native + 매 TypeScript-first"**. Eduardo San Martin Morote 매 2019 발표 매 Vue Core 팀 채택, 매 store 매 composable function 매 표현 매 boilerplate 90% 감소, 매 2026 매 Vue 표준 store library.

## 매 핵심

### 매 vs Vuex
- **No mutations**: 매 actions 가 directly state 수정 — 매 mutation indirection 제거.
- **Flat stores**: 매 nested module 매 X — 매 cross-store import 매 graph 형성.
- **Type inference**: 매 zero manual typing — 매 store usage 매 fully typed.
- **Devtools**: 매 timeline + state inspect + time-travel 지원.

### 매 store kinds
- **Options Store**: `state`, `getters`, `actions` — 매 Vuex-like familiar shape.
- **Setup Store**: `ref`/`computed`/`function` — 매 Composition API native.

### 매 응용
1. SPA global state (auth, user prefs).
2. Server-side rendering (Nuxt 3 매 native integration).
3. Cross-component caching (API result, derived state).
4. Plugin extension (persistedstate, undo/redo).

## 💻 패턴

### Setup store (modern preferred)
```ts
// stores/counter.ts
import { defineStore } from 'pinia'
import { ref, computed } from 'vue'

export const useCounterStore = defineStore('counter', () => {
  const count = ref(0)
  const doubled = computed(() => count.value * 2)
  function increment() { count.value++ }
  function reset() { count.value = 0 }
  return { count, doubled, increment, reset }
})
```

### Options store
```ts
export const useUserStore = defineStore('user', {
  state: () => ({
    user: null as User | null,
    loading: false,
  }),
  getters: {
    isLoggedIn: (s) => s.user !== null,
    displayName: (s) => s.user?.name ?? 'Guest',
  },
  actions: {
    async login(creds: Credentials) {
      this.loading = true
      try {
        this.user = await api.login(creds)
      } finally {
        this.loading = false
      }
    },
    logout() { this.user = null },
  },
})
```

### Component usage
```vue
<script setup lang="ts">
import { storeToRefs } from 'pinia'
import { useCounterStore } from '@/stores/counter'

const store = useCounterStore()
// 매 reactivity 매 유지: storeToRefs 매 ref 변환
const { count, doubled } = storeToRefs(store)
// actions 매 destructure OK (not reactive)
const { increment } = store
</script>

<template>
  <button @click="increment">{{ count }} (×2 = {{ doubled }})</button>
</template>
```

### App setup (Vue 3)
```ts
// main.ts
import { createApp } from 'vue'
import { createPinia } from 'pinia'
import App from './App.vue'

const app = createApp(App)
app.use(createPinia())
app.mount('#app')
```

### Cross-store usage
```ts
import { useAuthStore } from './auth'

export const useCartStore = defineStore('cart', () => {
  const auth = useAuthStore() // 매 다른 store 매 import + use
  const items = ref<CartItem[]>([])

  async function checkout() {
    if (!auth.isLoggedIn) throw new Error('Login required')
    return api.checkout(auth.user!.id, items.value)
  }
  return { items, checkout }
})
```

### $patch 매 batch update
```ts
const store = useUserStore()
store.$patch({ loading: false, user: newUser }) // 매 single devtools entry
// or function form for complex mutations
store.$patch((state) => {
  state.cart.push(item)
  state.lastUpdated = Date.now()
})
```

### $subscribe 매 store mutation 감지
```ts
store.$subscribe((mutation, state) => {
  localStorage.setItem('cart', JSON.stringify(state))
}, { detached: true })
```

### Plugin (persistedstate)
```ts
import { createPinia } from 'pinia'
import piniaPersist from 'pinia-plugin-persistedstate'

const pinia = createPinia()
pinia.use(piniaPersist)

// store 정의 시:
export const useUserStore = defineStore('user', {
  state: () => ({ token: '' }),
  persist: true, // localStorage 매 자동 sync
})
```

### SSR (Nuxt 3)
```ts
// composables/useAuth.ts
export const useAuthStore = defineStore('auth', () => {
  const user = ref<User | null>(null)
  // 매 Nuxt 3 매 자동 hydration — server 매 set 한 state 매 client 매 transfer
  return { user }
})
```

### Testing
```ts
import { setActivePinia, createPinia } from 'pinia'
import { beforeEach, expect, test } from 'vitest'

beforeEach(() => setActivePinia(createPinia()))

test('counter increments', () => {
  const store = useCounterStore()
  expect(store.count).toBe(0)
  store.increment()
  expect(store.count).toBe(1)
  expect(store.doubled).toBe(2)
})
```

## 매 결정 기준
| 상황 | Approach |
|---|---|
| Vue 3 new project | Pinia (default) |
| Vuex 4 migration | Pinia (incremental, alias module) |
| Composition API preference | Setup store |
| Vuex-familiar team | Options store |
| Component-local state | `ref`/`reactive` (no store) |
| Server state caching | TanStack Query / 매 store 의 X |
| SSR (Nuxt) | Pinia (built-in support) |

**기본값**: 매 setup store + TypeScript + storeToRefs.

## 🔗 Graph
- 부모: [[State Management]]
- 변형: [[Vuex]] (predecessor) · [[프론트엔드 및 UIUX 표준|Redux]] · [[Zustand]] · [[Jotai]]
- 응용: [[Nuxt]]
- Adjacent: [[Composition-API]]

## 🤖 LLM 활용
**언제**: 매 Vue 3 global state, 매 cross-component sharing, 매 Nuxt 3 SSR state, 매 Vuex migration target.
**언제 X**: 매 component-local state (ref 만 충분), 매 server cache (TanStack Query 적합), 매 React project (Zustand/Redux).

## ❌ 안티패턴
- **storeToRefs 없이 destructure**: 매 reactivity loss — 매 `const { count } = store` 의 X.
- **Store action 매 component logic 침범**: 매 store 매 단순 state holder 매 됨 — 매 business logic 매 store 에 응집.
- **Nested store hierarchy 시도**: 매 flat 의 X — 매 cross-import 매 graph 형성.
- **Mutation pattern 의 반복**: 매 Vuex habit — 매 action 에서 직접 state 수정 OK.
- **매 component 매 store instance 다중 생성**: 매 useStore() 매 singleton — 매 매 호출 동일 instance.

## 🧪 검증 / 중복
- Verified (Pinia 2.x docs, Vue.js official).
- 신뢰도 A.

## 🕓 Changelog
| 날짜 | 변경 |
|---|---|
| 2026-05-08 | Phase 1 |
| 2026-05-10 | Manual cleanup — setup/options store + cross-store + SSR + plugin patterns |