102 lines
2.1 KiB
Markdown
102 lines
2.1 KiB
Markdown
---
|
||
id: 5cfa550e84205a357704ccb6
|
||
title: 使用解構賦值來獲取對象的值
|
||
challengeType: 1
|
||
forumTopicId: 301216
|
||
dashedName: use-destructuring-assignment-to-extract-values-from-objects
|
||
---
|
||
|
||
# --description--
|
||
|
||
<dfn>解構賦值</dfn>是 ES6 引入的新語法，用來從數組和對象中提取值，並優雅地對變量進行賦值。
|
||
|
||
有如下 ES5 代碼：
|
||
|
||
```js
|
||
const user = { name: 'John Doe', age: 34 };
|
||
|
||
const name = user.name;
|
||
const age = user.age;
|
||
```
|
||
|
||
`name` 的值應該是字符串 `John Doe`， `age` 的值應該是數字 `34`。
|
||
|
||
下面是使用 ES6 解構賦值語句，實現相同效果：
|
||
|
||
```js
|
||
const { name, age } = user;
|
||
```
|
||
|
||
同樣，`name` 的值應該是字符串 `John Doe`， `age` 的值應該是數字 `34`。
|
||
|
||
在這裏，自動創建 `name` 和 `age` 變量，並將 `user` 對象相應屬性的值賦值給它們。 這個方法簡潔多了。
|
||
|
||
你可以從對象中提取儘可能多或很少的值。
|
||
|
||
# --instructions--
|
||
|
||
把兩個賦值語句替換成效果相同的解構賦值語句。 `today` 和 `tomorrow` 的值應該還是 `HIGH_TEMPERATURES` 對象中 `today` 和 `tomorrow` 屬性的值。
|
||
|
||
# --hints--
|
||
|
||
應該移除 ES5 賦值語句。
|
||
|
||
```js
|
||
assert(
|
||
!code.match(/today\s*=\s*HIGH_TEMPERATURES\.(today|tomorrow)/g)
|
||
);
|
||
```
|
||
|
||
應該使用解構賦值創建 `today` 變量。
|
||
|
||
```js
|
||
assert(
|
||
code.match(/(var|let|const)\s*{\s*(today[^}]*|[^,]*,\s*today)\s*}\s*=\s*HIGH_TEMPERATURES(;|\s+|\/\/)/g)
|
||
);
|
||
```
|
||
|
||
應該使用解構賦值創建 `tomorrow` 變量。
|
||
|
||
```js
|
||
assert(
|
||
code.match(/(var|let|const)\s*{\s*(tomorrow[^}]*|[^,]*,\s*tomorrow)\s*}\s*=\s*HIGH_TEMPERATURES(;|\s+|\/\/)/g)
|
||
);
|
||
```
|
||
|
||
`today` 應該等於 `77`，`tomorrow` 應該等於 `80`。
|
||
|
||
```js
|
||
assert(today === 77 && tomorrow === 80);
|
||
```
|
||
|
||
# --seed--
|
||
|
||
## --seed-contents--
|
||
|
||
```js
|
||
const HIGH_TEMPERATURES = {
|
||
yesterday: 75,
|
||
today: 77,
|
||
tomorrow: 80
|
||
};
|
||
|
||
// Only change code below this line
|
||
|
||
const today = HIGH_TEMPERATURES.today;
|
||
const tomorrow = HIGH_TEMPERATURES.tomorrow;
|
||
|
||
// Only change code above this line
|
||
```
|
||
|
||
# --solutions--
|
||
|
||
```js
|
||
const HIGH_TEMPERATURES = {
|
||
yesterday: 75,
|
||
today: 77,
|
||
tomorrow: 80
|
||
};
|
||
|
||
const { today, tomorrow } = HIGH_TEMPERATURES;
|
||
```
|