---
tags: Vue 直播班 - 2023 冬季班
---
# 🏅 Day 14 - 箭頭函式
參考文章: https://wcc723.github.io/javascript/2017/12/21/javascript-es6-arrow-function/
### 教學
箭頭函式的運用技巧如下：
```js=
// 傳統函式
function saySomething(string) {
return '接招' + string;
}
// 轉成箭頭函式
const saySomething = (string) => {
return '接招 ' + string;
}
```
```js=
// 當只有單行表達式時，可同時省略 return 及 {}
// 省略後依然保有回傳的特質
const saySomething = (string) => '接招 ' + string;
console.log(saySomething('菜鳥!'));
// 不過要注意，如果有使用 {}，就需要自行加上 return
const saySomething = (string) => {'接招 ' + string};
console.log(saySomething('菜鳥!')); // 會回傳 undefined
```
```js=
// 只有一個參數可以不加括號 ()
const saySomething = string => '接招 ' + string;
console.log(saySomething('菜鳥!'));
// 沒有參數、參數有兩個以上都不能省略 ()
const saySomething = () => '接招 菜鳥!';
console.log(saySomething());
```
題目
---
請將以下程式碼簡化為箭頭函式 (不影響結果的情況下進行最大簡化)
```js=
// 題目一
function sum(a, b) {
let c = a + b;
return c;
}
console.log(sum(5, 6));
// 題目二
function square(num) {
return num * num;
}
console.log(square(5))
// 題目三
setTimeout(function() {
console.log('延遲 1 秒');
}, 1000);
// 題目四
let arr = [1, 2, 3];
let arrNew = arr.map(function(item, i) {
return item * i;
});
console.log(arrNew);
// 題目五
let obj = {
fn: function fn2(a) {
return a * a;
}
}
console.log(obj.fn(10));
```
## 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：
// 題目一
const sum = (a, b) => {
let c = a + b;
return c;
}
這題解答怪怪的，應該是↓ 有錯麻煩糾正，謝謝。 by同學
const sum = (a, b) => a+b;
console.log(sum(5, 6));
// 題目二
let square = num => num * num;
console.log(square(5));
// 題目三
setTimeout(() => console.log('延遲 1 秒'), 1000);
// 題目四
let arr = [1, 2, 3];
let arrNew = arr.map((item, i) => item * i);
console.log(arrNew);
// 題目五
let obj = {
fn: a => a * a
}
console.log(obj.fn(10));
-->
回報區
---
| Discord | CodePen / 答案 |
|:---------------:|:----------------------------------------------------------------------------:|
| Yijing | [CodePen](https://codepen.io/Yi-Jing-71080635/pen/gOEPONw?editors=0010) |
| bf_tsai | [CodePen](https://codepen.io/BF-Tsai/pen/BabjpaB?editors=1111) |
| kj | [CodePen](https://codepen.io/Eero-Chiao/pen/XWGXpWe) |
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| py | [CodePen](https://codepen.io/Wpypy/pen/yLwegBV?editors=1011) |
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| kawa | [CodePen](https://codepen.io/z83xji6/pen/oNVbBzQ?editors=0011) |
| ryan.chou | [CodePen](https://codepen.io/csw8524/pen/QWoyddK) |
| Emily | [CodePen](https://codepen.io/Emily2089/pen/MWxKJrO) |
| Leo | [CodePen](https://codepen.io/Aruminiya/pen/eYXJgKM) |
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| XinYu | [CodePen](https://codepen.io/HsuXinYu/pen/oNVbZjN?editors=0012) |
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| KUN. | [CodePen](https://codepen.io/barry91205/pen/abMdJGz?editors=1111) |
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| hedy | [CodePen](https://codepen.io/Hedy_H/pen/VwRepyK?editors=0012) |
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| cest_jessie | [CodePen](https://codepen.io/itsjessiechen/pen/XWGXMbo) |
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| Peng | [CodePen](https://codepen.io/H-Peng/pen/LYaGXQM?editors=0011) |
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| 保羅|[CodePen](https://codepen.io/paul-1997/pen/vYPLbOJ?editors=0011)
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| carrie | [CodePen](https://codepen.io/echocarriet/pen/oNVbJax) |
| 小夏 | [CodePen](https://codepen.io/michaelhsia/pen/KKEVjmN) |
| jia yu | [CodePen](https://codepen.io/fjqxaznl-the-reactor/pen/XWGdKZV?editors=0010) |
| Ting | [CodePen](https://codepen.io/liara/pen/xxBVgEp)|
| skypassion5000 | [CodePen](https://codepen.io/skypassion5000/pen/zYbqPqz?editors=0011)|
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| 狸貓 | [CodePen](https://codepen.io/tanuki320/pen/BabQJzg?editors=1111) |
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