81 lines
1.1 KiB
Markdown
81 lines
1.1 KiB
Markdown
|
---
|
||
|
|
id: 56533eb9ac21ba0edf2244ad
|
||
|
|
title: 數字遞減
|
||
|
|
challengeType: 1
|
||
|
|
videoUrl: 'https://scrimba.com/c/cM2KeS2'
|
||
|
|
forumTopicId: 17558
|
||
|
|
dashedName: decrement-a-number-with-javascript
|
||
|
|
---
|
||
|
|
|
||
|
|
# --description--
|
||
|
|
|
||
|
|
使用自減符號 `--`，你可以很方便地對一個變量執行<dfn>自減</dfn>或者 -1 運算。
|
||
|
|
|
||
|
|
```js
|
||
|
|
i--;
|
||
|
|
```
|
||
|
|
|
||
|
|
等效於：
|
||
|
|
|
||
|
|
```js
|
||
|
|
i = i - 1;
|
||
|
|
```
|
||
|
|
|
||
|
|
**注意：**`i--;` 這種寫法省去了書寫等號的必要。
|
||
|
|
|
||
|
|
# --instructions--
|
||
|
|
|
||
|
|
修改代碼，使用 `--` 符號對 `myVar` 執行自減操作。
|
||
|
|
|
||
|
|
# --hints--
|
||
|
|
|
||
|
|
`myVar` 應該等於`10`。
|
||
|
|
|
||
|
|
```js
|
||
|
|
assert(myVar === 10);
|
||
|
|
```
|
||
|
|
|
||
|
|
應該修改 `myVar = myVar - 1;`。
|
||
|
|
|
||
|
|
```js
|
||
|
|
assert(
|
||
|
|
/var\s*myVar\s*=\s*11;\s*\/*.*\s*([-]{2}\s*myVar|myVar\s*[-]{2});/.test(code)
|
||
|
|
);
|
||
|
|
```
|
||
|
|
|
||
|
|
應該對 `myVar` 使用 `--` 運算符。
|
||
|
|
|
||
|
|
```js
|
||
|
|
assert(/[-]{2}\s*myVar|myVar\s*[-]{2}/.test(code));
|
||
|
|
```
|
||
|
|
|
||
|
|
不應修改註釋上方的代碼。
|
||
|
|
|
||
|
|
```js
|
||
|
|
assert(/var myVar = 11;/.test(code));
|
||
|
|
```
|
||
|
|
|
||
|
|
# --seed--
|
||
|
|
|
||
|
|
## --after-user-code--
|
||
|
|
|
||
|
|
```js
|
||
|
|
(function(z){return 'myVar = ' + z;})(myVar);
|
||
|
|
```
|
||
|
|
|
||
|
|
## --seed-contents--
|
||
|
|
|
||
|
|
```js
|
||
|
|
var myVar = 11;
|
||
|
|
|
||
|
|
// Only change code below this line
|
||
|
|
myVar = myVar - 1;
|
||
|
|
```
|
||
|
|
|
||
|
|
# --solutions--
|
||
|
|
|
||
|
|
```js
|
||
|
|
var myVar = 11;
|
||
|
|
myVar--;
|
||
|
|
```
|