---
tags: 2022 React 新手讀書會
---
# 🏅 Day 3｜React Hook - useState
今日我們要進入 React Hook，並嘗試用 useState 這個 Hook 來做出改變狀態值的練習。
### React Hook
Hook 其實就是 JavaScript function，但要特別注意兩個使用的規則：
1. 只在最上層呼叫 Hook，不要在迴圈、條件式或是巢狀的 function 內呼叫 Hook（[詳細解說](https://zh-hant.reactjs.org/docs/hooks-rules.html#explanation)）
2. 只在 React Function 中呼叫 Hook，例如：在 React function component 中呼叫 Hook。

今日的練習我們會著重在規則二，也就是練習『在 React function component 中呼叫 Hook』。

### React function component

function Example() {
    // 在這邊使用 Hook
  return (
    // 在這邊加入 Template，例如：
    <p>Hello</p>
  )
}
const root = ReactDOM.createRoot(document.getElementById('root'));
root.render(<Example />);

### useState
useState 是被用來加入一些基礎的變數狀態。useState 會回傳一組數值：目前 state 數值和一個可以更新 state 的方法，寫法如下：

const [count, setCount] = React.useState(0);

透過 setCount 方法可以改變 count 的值

setCount(count + 1)

### 補充：JSX 的事件綁定
在 JSX 中，事件綁定是以小駝峰的方式命名（camelCase），因此 onclick 事件即為 onClick、onchange 事件為 onChange。

<button onClick={() => {}}> 按鈕 </button>

[參考：Hook 的規則](https://zh-hant.reactjs.org/docs/hooks-rules.html)

## 題目
請複製 （右下角 fork）這個[範例](https://codepen.io/hexschool/pen/VwXYKZY)，並撰寫內容，完成以下畫面：


## 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：

function Example() {
  // 宣告一個新的 state 變數，我們叫他「count」
  const [count, setCount] = React.useState(0);

  return (
    <div>
      <p>現在的數字是 {count} </p>
      <button onClick={() => setCount(count + 1)}>
        加一
      </button>
      <button onClick={() => setCount(count - 1)}>
        減一
      </button>
    </div>
  );
}

-->

回報區
---

| Discord | CodePen / 答案 |
|:----------------------- |:---------------------------------------------------------------------------- |
| Rice#8043 | [Codepen](https://codepen.io/riecball/pen/LYdjxLz?editors=1010) |
| Joechiboo#3960 | [Codepen](https://codepen.io/joe-chiboo/pen/VwXQVeo) |
| yunyun#5215 | [Codepen](https://codepen.io/yun_yunni/pen/vYRdQxO) |
| DIANAxAKKO#4298 | [Codepen](https://codepen.io/redfire29/pen/GRxQwQj?editors=1010) |
| 布魯諾#7239 | [Codepen](https://codepen.io/bruno-yu/pen/rNdJQmq) |
| LEO#7779 | [Codepen](https://codepen.io/nekorice/pen/oNqEQZK) |
| 魚魚#0937 | [Codepen](https://codepen.io/fish0522/pen/KKoQrWZ) |
| AllenW#1132 | [Codepen](https://codepen.io/AllenW/pen/LYdQXBE?editors=1011) |
| HedgehogKU | [CodePen](https://codepen.io/hedgehogkucc/pen/KKoQrrB?editors=1010) |
| 棒腿#9350 | [Codepen](https://codepen.io/frankHsu/pen/LYdQXMV) |
| JarDar#6980 | [codepen](https://codepen.io/jardarpen/pen/oNqEQVb) |
| Carolkiki2003#7399 | [codepen](https://codepen.io/wasfzuig/pen/gOevQyR) |
| wiimax#4564 | [Codepen](https://codepen.io/willismax/pen/RwMQqmK) |
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| Evonne#7078 | [codePen](https://codepen.io/Hsu1Fang/pen/gOevQJR?editors=1011) |
| Yukon#2618 | [codePen](https://codepen.io/ukowork/pen/abYqQMo) |
| m_m#5493 | [Codepen](https://codepen.io/minnn7716/pen/qBoxLZZ) |
| Kimi#2092 | [Codepen](https://codepen.io/a3216lucy/pen/rNdJoOX) |
| Eric Su#7798 | [Codepen](https://codepen.io/wc-su/pen/GRxQPJv) |
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| Ayre#0016 | [Codepen](https://codepen.io/yichunlin09/pen/BarYvLx?editors=0010) |
| L0F0#8733 | [Codepen](https://codepen.io/l0f0/pen/ExEQGWV?editors=0010) |
| Kenge#3690 | [Codepen](https://codepen.io/pgkusn/pen/VwXQqWW) |
| 小熊#0685 | [Codepen](https://codepen.io/YuHan0704/pen/yLKvGJr?editors=1010) |
| kevinhes#2881 | [CodePen](https://codepen.io/kevinhes/pen/qBoxLxR?editors=0010) |
| Mickey Hsu #9693 | [CodePen](https://codepen.io/kikmiao1995/pen/jOzZXzo) |
| 連小艾#0791 | [Codepen](https://codepen.io/bolaslien/pen/abYqPRB?editors=0010) |
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| hiYifang #0736 | [Codepen](https://codepen.io/hiYifang/pen/zYWReZd) |
| JC#8658 | [Codepen](https://codepen.io/jcsamoyed/pen/bGvLOXy) |
| Vada Chen#2055 | [Codepen](https://codepen.io/vadachen/pen/ZExrwxy) |
| RON#2813 | [Codepen](https://codepen.io/Ron115/pen/OJvQrLO) |
| claire#2116 | [Codepen](https://codepen.io/claire-chang-the-bashful/pen/ZExrPEr) |
| 無名#6427 | [Codepen](https://codepen.io/Nomoney/pen/WNzMLBq?editors=1010) |
| Morris#8755 | [Codepen](https://codepen.io/morrisss/pen/dymdrpx) |
| 喬喬#2824 | [Codepen](https://codepen.io/joanne-wei/pen/PoRQVeY?editors=1010) |
| Yanyan#3555 | [Codepen](https://codepen.io/wei-yi-lee/pen/MWVQxJG) |
| EvaLin#4546 | [Codepen](https://codepen.io/evalin0316/pen/vYRdPdL?editors=1111) |
| Mitour#0672 | [CodePen](https://codepen.io/mitour/pen/KKoQEOG?editors=1010) |
| Overy#4545 | [Codepen](https://codepen.io/oceanwhale52hz/pen/wvmyORP) |
| Ｎico#8739 | [Codepen](https://codepen.io/Nicof2e/pen/vYRdPwy) |
| 吉利#3810 | [CodePen](https://codepen.io/gillianyy/pen/OJvQGyz) |
| React-慧茹(拉拉醬)#3414 | [Codepen](https://codepen.io/lala-lee-jobs/pen/BarYEjr) |
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| IreneLee#7932 | [Codepen](https://codepen.io/ntjtcxpt-the-animator/pen/QWmQRed?editors=1010) |
| Yiling#4054 | [Codepen](https://codepen.io/lin010/pen/VwXQJWw?editors=1010) |
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| Midnightdinner#6220 | [Codepen](https://codepen.io/woowooyong/pen/MWVQMLz) |
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| Arista#5802 | [Codepen](https://codepen.io/arista-hsieh/pen/zYWRgjr) |
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| Yihan#5560 | [Codepen](https://codepen.io/h513hh513h/pen/jOzZgKo?editors=0011) |
| Ryder#7398 | [Codepen](https://codepen.io/rider159159/pen/QWmmLyW?editors=1010) |
| 史蒂夫#5075 | [Codepen](https://codepen.io/TaroPanda/pen/PoRRYdY) |
| easton#3863 | [Codepen](https://codepen.io/EastonIsCodingNow/pen/xxWWKBJ) |
| shin#5792 | [Codepen](https://codepen.io/hah1030/pen/XWEEWdB?editors=1010) |
| huch09#1426 | [Codepen](https://codepen.io/subarashii-huch09/pen/GRxxRqp?editors=0010) |
| 𝔼.𝕎#4742 | [Codepen](https://codepen.io/kidult316/pen/mdxxywq) |
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| Chelly#6129 | [Codepen](https://codepen.io/chellyhsu/pen/LYddPKM) |
| minmin#8960 | [Codepen](https://codepen.io/minfan-chen/pen/BarrNyb) |
| lingxuan | [Codepen](https://codepen.io/lingxuan0618/pen/KKoopQM) |
| hw#0715 | [Codepen](https://codepen.io/Lhwei/pen/XWEZovN) |
| CofCat#9226 | [Codepen](https://codepen.io/cofcat456/pen/yLKKNZb?editors=1010) |
| yunyun#2239 | [Codepen](https://codepen.io/jarita0826/pen/Barroaj) |
| Sylvia-H #0024 | [Codepen](https://codepen.io/Cosmosheart/pen/QWmmbed) |
| 紅豆豆 #0518 | [Codepen](https://codepen.io/zoseqlpc/pen/XWEEmjB?editors=0010) |
| hobby #6565 | [Codepen](https://codepen.io/hobbyling/pen/WNzzQxp) |
| 芝麻凜#1627 | [Codepen](https://codepen.io/bardkidd/pen/oNqqjYR?editors=0010) |
| Wu#0167 | [Codepen](https://codepen.io/Xander0705/pen/WNzzQZE) |
| Stanley#2505 | [Codepen](https://codepen.io/bigbearada/pen/MWVVaxP) |
| kyle890721#1016 | [Codepen](https://codepen.io/KYLE890721/pen/yLKKeVw) |
| 阿暟 | [Codepen](https://codepen.io/patrickrrr007/pen/OJvvMEw?editors=1010) |
| yiwun#0953 | [Codepen](https://codepen.io/kagamiakira_IBUN/pen/MWVVKmd) |
| Evileye#0666 | [Codepen](https://codepen.io/gn-lin/pen/wvmmKXe?editors=1010) |
| hungya#0773 | [Codepen](https://codepen.io/hungya777/pen/jOzzNoy?editors=1010) |
| Anson #3594 | [Codepen](https://codepen.io/huanmingchang/pen/dymmvjR?editors=1010) |
| ねこ*#9385 | [Codepan](https://codepen.io/kunpao0104/pen/KKoomNp) |
| lloydd#8224 | [Codepen](https://codepen.io/thanatus25/pen/poLLPxN) |
| 𝓛𝓊𝒸𝓎#8635 | [Codepen](https://codepen.io/lucygirl/pen/MWVVoaE) |
| IceSam#7836 | [Codepen](https://codepen.io/sam-hsu/pen/vYRRZgB) |
| Kunda#2800 | [Codepen](https://codepen.io/kunda0818/pen/ExEEXKp?editors=0010) |
| east#4003 | [Codepen](https://codepen.io/EastM/pen/mdxxwxV) |
| larahuang#8309 | [Codepen](https://codepen.io/lara1105huang/pen/YzaaQZK) |
| TaoDoris#5230 | [Codepen](https://codepen.io/taomaomao/pen/rNddzME?editors=0010) |
| andersonshen#4675 | [Codepen](https://codepen.io/luxyenni-the-bold/pen/wvmmrLK) |
| zzly#9134 | [Codepen](https://codepen.io/ly00/pen/GRxxOpR) |
| Shau#6400 | [Codepen](https://codepen.io/shau-chen/pen/xxWWPYB) |
| 山貓(焜)#7041 | [Codepen](https://codepen.io/pen?template=bGvvYvW) |
| Vivi0225#3634 | [Codepen](https://codepen.io/vivian820225/pen/KKoQJWz) |
| 眼睛 #0314 | [Codepen](https://codepen.io/thrizzacode/pen/poLLaJo) |
| fannnny#7112 | [Codepen](https://codepen.io/vivian820225/pen/KKoQJWz) |
| JimHwang#3594 | [Codepen](https://codepen.io/jimh1129/pen/wvmmXvN) |
| 城堡#2126 | [Codepen](https://codepen.io/tthcastle/pen/wvmmXgb) |
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| DaleHsu#0355 | [Codepen](https://codepen.io/dale_hsu/pen/VwXXBxw) |
| LinaChen#1796 | [Codepen](https://codepen.io/LinaChen/pen/ZExxKxe) |
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| POKA #2168 | [Codepen](https://codepen.io/POKAHSIAO/pen/JjLLmLM) |
| JessSong#5050 | [Codepen](https://codepen.io/jssanji03/pen/mdxxdxE) |
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| seijo #1585 | [Codepen](https://codepen.io/SeijoHuang/pen/yLKKwJo?editors=1010) |
| Robert Lo#9653 | [Codepen](https://codepen.io/Robert-Lo/pen/GRxxebN) |
| Evachan#5729 | [Codepen](https://codepen.io/Eva-go/pen/OJvvKgO?editors=1010) |
| 彼得#1923 | [Codepen](https://codepen.io/shiou-ho/pen/NWYMKoq) |
| Tsuei#9284 | [Codepen](https://codepen.io/AlbertoLL/pen/GRxdgxM?editors=1010) |
| 翔#0859 | [Codepen](https://codepen.io/energy95272z/pen/jOzxEed) |
| kir4che#7701 | [Codepen](https://codepen.io/kir4che/details/qBoYEMN) |
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| moitw | [codepen](https://codepen.io/tsuifei/pen/mdxLepy?editors=1010) |
| Carol Li #2269 | [Codepen](https://codepen.io/carolli834/pen/ZExobdM?editors=1010) |
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| Renren #8437 | [Codepen](https://codepen.io/ehren-chen/pen/XWEqPMG) |
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