2018-10-10 22:03:03 +00:00
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---
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id: 56533eb9ac21ba0edf2244ba
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2021-03-15 03:20:39 +00:00
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title: 了解字符串的不变性
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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/cWPVaUR'
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forumTopicId: 18331
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2021-01-13 02:31:00 +00:00
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dashedName: understand-string-immutability
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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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2021-03-15 03:20:39 +00:00
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在 JavaScript 中,字符串(`String`)的值是不可变的(<dfn>immutable</dfn>),这意味着一旦字符串被创建就不能被改变。
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2020-12-16 07:37:30 +00:00
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2021-03-15 03:20:39 +00:00
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例如,下面的代码:
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2020-04-29 10:29:13 +00:00
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```js
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var myStr = "Bob";
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myStr[0] = "J";
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```
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2021-03-15 03:20:39 +00:00
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是不会把变量 `myStr` 的值改变成 `Job` 的,因为变量 `myStr` 是不可变的。 注意,这*并不*意味着 `myStr` 永远不能被改变,只是字符串字面量 <dfn>string literal</dfn> 的各个字符不能被改变。 改变 `myStr` 的唯一方法是重新给它赋一个值,例如:
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2020-04-29 10:29:13 +00:00
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```js
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var myStr = "Bob";
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myStr = "Job";
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```
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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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更正对 `myStr` 的分配,使用上面示例中的方法包含 `Hello World` 字符串。
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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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`myStr` 的值应该是字符串 `Hello World`。
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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(myStr === 'Hello World');
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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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不要修改注释上面的代码。
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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(/myStr = "Jello World"/.test(code));
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2018-10-10 22:03:03 +00:00
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```
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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(v){return "myStr = " + v;})(myStr);
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```
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## --seed-contents--
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```js
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// Setup
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var myStr = "Jello World";
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// Only change code below this line
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myStr[0] = "H"; // Change this line
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// Only change code above this line
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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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2020-04-29 10:29:13 +00:00
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2021-01-13 02:31:00 +00:00
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```js
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var myStr = "Jello World";
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myStr = "Hello World";
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```
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