npm install pinia

// main.js
import { createApp } from 'vue'
import { createPinia } from 'pinia'
import App from './App.vue'

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

// stores/counter.js
import { defineStore } from 'pinia'

export const useCounterStore = defineStore('counter', {
  state: () => ({
    count: 0,
    name: 'Counter'
  }),
  
  getters: {
    doubleCount: (state) => state.count * 2,
    greeting: (state) => `Hello, ${state.name}!`
  },
  
  actions: {
    increment() {
      this.count++
    },
    
    async fetchData() {
      // 異步操作
      const data = await fetch('/api/data')
      this.count = data.count
    }
  }
})

<template>
  <div>
    <p>計數(shù): {{ counter.count }}</p>
    <p>雙倍: {{ counter.doubleCount }}</p>
    <button @click="counter.increment()">增加</button>
  </div>
</template>

<script setup>
import { useCounterStore } from '@/stores/counter'

const counter = useCounterStore()
</script>

// stores/user.js
import { defineStore } from 'pinia'

export const useUserStore = defineStore('user', {
  state: () => ({
    user: null,
    token: localStorage.getItem('token'),
    isLoading: false
  }),
  
  getters: {
    isAuthenticated: (state) => !!state.token,
    userName: (state) => state.user?.name || '游客'
  },
  
  actions: {
    async login(credentials) {
      this.isLoading = true
      try {
        const response = await fetch('/api/login', {
          method: 'POST',
          body: JSON.stringify(credentials)
        })
        const data = await response.json()
        
        this.user = data.user
        this.token = data.token
        localStorage.setItem('token', data.token)
      } finally {
        this.isLoading = false
      }
    },
    
    logout() {
      this.user = null
      this.token = null
      localStorage.removeItem('token')
    }
  }
})

// stores/cart.js
import { defineStore } from 'pinia'

export const useCartStore = defineStore('cart', {
  state: () => ({
    items: []
  }),
  
  getters: {
    totalItems: (state) => state.items.reduce((sum, item) => sum + item.quantity, 0),
    totalPrice: (state) => state.items.reduce((sum, item) => sum + item.price * item.quantity, 0)
  },
  
  actions: {
    addItem(product) {
      const existingItem = this.items.find(item => item.id === product.id)
      
      if (existingItem) {
        existingItem.quantity++
      } else {
        this.items.push({ ...product, quantity: 1 })
      }
    },
    
    removeItem(productId) {
      const index = this.items.findIndex(item => item.id === productId)
      if (index > -1) {
        this.items.splice(index, 1)
      }
    },
    
    clearCart() {
      this.items = []
    }
  }
})

// stores/theme.js
import { defineStore } from 'pinia'

export const useThemeStore = defineStore('theme', {
  state: () => ({
    isDark: localStorage.getItem('theme') === 'dark'
  }),
  
  getters: {
    theme: (state) => state.isDark ? 'dark' : 'light'
  },
  
  actions: {
    toggleTheme() {
      this.isDark = !this.isDark
      localStorage.setItem('theme', this.theme)
      document.documentElement.setAttribute('data-theme', this.theme)
    },
    
    setTheme(theme) {
      this.isDark = theme === 'dark'
      localStorage.setItem('theme', theme)
      document.documentElement.setAttribute('data-theme', theme)
    }
  }
})

// stores/posts.js
import { defineStore } from 'pinia'

export const usePostsStore = defineStore('posts', {
  state: () => ({
    posts: [],
    loading: false,
    error: null
  }),
  
  getters: {
    publishedPosts: (state) => state.posts.filter(post => post.published),
    getPostById: (state) => (id) => state.posts.find(post => post.id === id)
  },
  
  actions: {
    async fetchPosts() {
      this.loading = true
      this.error = null
      
      try {
        const response = await fetch('/api/posts')
        this.posts = await response.json()
      } catch (error) {
        this.error = error.message
      } finally {
        this.loading = false
      }
    },
    
    async createPost(postData) {
      const response = await fetch('/api/posts', {
        method: 'POST',
        body: JSON.stringify(postData)
      })
      const newPost = await response.json()
      this.posts.push(newPost)
    }
  }
})

// Pinia - 簡潔直觀
const store = useStore()
store.count++
store.updateUser(userData)

// Vuex - 需要 commit
store.commit('INCREMENT')
store.dispatch('updateUser', userData)

// 推薦：use + 功能名 + Store
export const useUserStore = defineStore('user', {})
export const useCartStore = defineStore('cart', {})
export const useThemeStore = defineStore('theme', {})

// 推薦：扁平化狀態(tài)結構
state: () => ({
  user: null,
  isLoading: false,
  error: null
})

// 避免：過度嵌套
state: () => ({
  user: {
    profile: {
      personal: {
        name: ''
      }
    }
  }
})

<script setup>
import { useUserStore } from '@/stores/user'
import { useCartStore } from '@/stores/cart'

const userStore = useUserStore()
const cartStore = useCartStore()

// 可以在 actions 中調用其他 store
const handlePurchase = () => {
  if (userStore.isAuthenticated) {
    cartStore.clearCart()
  }
}
</script>

// 簡單的持久化實現(xiàn)
export const useSettingsStore = defineStore('settings', {
  state: () => ({
    language: 'zh-CN',
    notifications: true
  }),
  
  actions: {
    updateSettings(settings) {
      Object.assign(this, settings)
      localStorage.setItem('settings', JSON.stringify(this.$state))
    },
    
    loadSettings() {
      const saved = localStorage.getItem('settings')
      if (saved) {
        Object.assign(this, JSON.parse(saved))
      }
    }
  }
})

// 重置整個 store
const store = useStore()
store.$reset()

// 重置特定狀態(tài)
store.$patch({
  count: 0,
  name: ''
})

// 在組件中監(jiān)聽
import { watch } from 'vue'

const store = useStore()

watch(
  () => store.count,
  (newCount) => {
    console.log('Count changed:', newCount)
  }
)

// 在 SSR 中使用
export const useStore = defineStore('main', {
  state: () => ({
    data: null
  }),
  
  actions: {
    async hydrate() {
      if (process.client && !this.data) {
        await this.fetchData()
      }
    }
  }
})