2018-10-10 22:03:03 +00:00
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---
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id: 56533eb9ac21ba0edf2244ad
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2021-03-15 03:20:39 +00:00
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title: 数字递减
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2018-10-10 22:03:03 +00:00
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challengeType: 1
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2020-04-29 10:29:13 +00:00
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videoUrl: 'https://scrimba.com/c/cM2KeS2'
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forumTopicId: 17558
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2021-01-13 02:31:00 +00:00
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dashedName: decrement-a-number-with-javascript
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2018-10-10 22:03:03 +00:00
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---
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2020-12-16 07:37:30 +00:00
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# --description--
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2018-10-10 22:03:03 +00:00
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2021-03-15 03:20:39 +00:00
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使用自减符号`--`,你可以很方便地对一个变量执行<dfn>自减</dfn>或者 -1 运算。
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2018-10-10 22:03:03 +00:00
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2020-12-16 07:37:30 +00:00
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`i--;`
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2018-10-10 22:03:03 +00:00
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2021-03-15 03:20:39 +00:00
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等效于
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2018-10-10 22:03:03 +00:00
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2020-12-16 07:37:30 +00:00
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`i = i - 1;`
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2018-10-10 22:03:03 +00:00
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2021-03-15 03:20:39 +00:00
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**提示** `i--;` 这种写法,省去了书写等号的必要。
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2018-10-10 22:03:03 +00:00
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2020-12-16 07:37:30 +00:00
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# --instructions--
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2018-10-10 22:03:03 +00:00
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2021-03-15 03:20:39 +00:00
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重写代码,使用 `--` 符号对 `myVar` 执行自减操作。
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2018-10-10 22:03:03 +00:00
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2020-12-16 07:37:30 +00:00
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# --hints--
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2018-10-10 22:03:03 +00:00
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2021-03-15 03:20:39 +00:00
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`myVar` 应该等于`10`。
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2018-10-10 22:03:03 +00:00
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```js
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assert(myVar === 10);
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2018-10-10 22:03:03 +00:00
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```
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2021-03-15 03:20:39 +00:00
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`myVar = myVar - 1;` 语句应该被修改。
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2018-10-10 22:03:03 +00:00
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2020-12-16 07:37:30 +00:00
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```js
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assert(
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/var\s*myVar\s*=\s*11;\s*\/*.*\s*([-]{2}\s*myVar|myVar\s*[-]{2});/.test(code)
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);
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```
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2018-10-10 22:03:03 +00:00
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2021-03-15 03:20:39 +00:00
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对 `myVar` 使用 `--` 运算符。
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2018-10-10 22:03:03 +00:00
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2020-12-16 07:37:30 +00:00
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```js
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assert(/[-]{2}\s*myVar|myVar\s*[-]{2}/.test(code));
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```
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2021-03-15 03:20:39 +00:00
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不要修改注释上面的代码。
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2020-04-29 10:29:13 +00:00
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2018-10-10 22:03:03 +00:00
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```js
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2020-12-16 07:37:30 +00:00
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assert(/var myVar = 11;/.test(code));
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2018-10-10 22:03:03 +00:00
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```
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2020-04-29 10:29:13 +00:00
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2021-01-13 02:31:00 +00:00
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# --seed--
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## --after-user-code--
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```js
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(function(z){return 'myVar = ' + z;})(myVar);
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```
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## --seed-contents--
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```js
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var myVar = 11;
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// Only change code below this line
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myVar = myVar - 1;
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```
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2020-12-16 07:37:30 +00:00
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# --solutions--
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2021-01-13 02:31:00 +00:00
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```js
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var myVar = 11;
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myVar--;
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```
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