---
tags: Vue 直播班 - 2023 冬季班
---
# 🏅 Day 27 - Pinia - 將 store 內資料渲染到畫面上
要讓元件可以取用 store 內的資料，我們需運用到 mapState() 方法，
若要對該資料進行一些計算的話，可以再搭配 getters
### 1. mapState()
我們只有單純要取用資料，所以會在元件中的 computed 中使用
```javascript=
// 取用方法
const { createPinia, defineStore, mapState } = Pinia
// 我們定義ㄉ store
const exampleStore = defineStore('exampleStoreId', {
state: () => {
return {
message: 'Pinia Pinia Pinia！'
}
}
})
// Vue app
const app = Vue.createApp({})
// 元件
app.component('WelcomeMessage', {
template: `<p>{{ message }}</p>`,
computed: {
// 使用 ... 展開的方式
// mapState() 第一個參數是我們要取用的 store，第二個參數是我們要取用的資料
...mapState(exampleStore, ['message'])
}
})
const pinia = createPinia();
app.use(pinia);
app.mount('#app');
```
> 觀看完整範例：https://codepen.io/hexschool/pen/eYjvRgM?editors=1011
### 2. 搭配 getters
```javascript=
// 取用方法
const { createPinia, defineStore, mapState } = Pinia
// 我們定義ㄉ store
const exampleStore = defineStore('exampleStoreId', {
state: () => {
return {
message: 'Pinia Pinia Pinia！'
}
},
getters: {
// 將 state 內資料使用解構方式帶入
printMessage: ({ message }) => {
// 可以對資料進行操作
return 'msg: ' + message
}
}
})
// Vue app
const app = Vue.createApp({})
// 元件
app.component('WelcomeMessage', {
template: `<p>{{ printMessage }}</p>`,
computed: {
// 這邊第二個參數是要使用 getters 內的函式名稱
...mapState(exampleStore, ['printMessage'])
}
})
const pinia = createPinia();
app.use(pinia);
app.mount('#app');
```
> 觀看完整範例：https://codepen.io/hexschool/pen/LYBWjYV?editors=1011
### 題目
請嘗試修改此[模板](https://codepen.io/hexschool/pen/XWBpBWY)（只能調整 `...` 的部分），讓畫面可以呈現出「總科目數：3」
#### 額外挑戰
完成上述題目後，嘗試將 JS 區塊改為使用 Composition API 撰寫
## 回報流程
將答案寫在 CodePen 並複製 CodePen 連結貼至底下回報就算完成了喔!
解答位置請參考下圖（需打開程式碼的部分觀看）
<!-- 解答：
https://codepen.io/hexschool/pen/dyjWyMa
額外挑戰：
https://codepen.io/jmimiding4104/pen/qBvdEYj?editors=1011
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---
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