82 lines
1.9 KiB
Markdown
82 lines
1.9 KiB
Markdown
---
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id: bd7123c9c452eddfaeb5bdef
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title: Use Bracket Notation to Find the Nth-to-Last Character in a String
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challengeType: 1
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videoUrl: 'https://scrimba.com/c/cw4vkh9'
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forumTopicId: 18344
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localeTitle: 使用方括号查找字符串中的第N个字符到最后一个字符
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---
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## Description
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<section id='description'>
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我们既可以获取字符串的最后一个字符，也可以用获取字符串的倒数第N个字符。
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例如，你可以这样<code>firstName[firstName.length - 3]</code>操作来获得<code>var firstName = "Charles"</code>字符串中的倒数第三个字符。
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</section>
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## Instructions
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<section id='instructions'>
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使用<dfn>方括号</dfn>来获得<code>lastName</code>字符串中的倒数第二个字符。
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<strong>提示</strong><br>如果你遇到困难了，不妨看看<code>thirdToLastLetterOfFirstName</code>变量是如何做到的。
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</section>
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## Tests
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<section id='tests'>
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```yml
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tests:
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- text: <code>secondToLastLetterOfLastName</code>应该是"c"。
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testString: assert(secondToLastLetterOfLastName === 'c');
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- text: 你需要使用<code>.length</code>获取倒数第二个字符。
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testString: assert(code.match(/\.length/g).length === 2);
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```
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</section>
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## Challenge Seed
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<section id='challengeSeed'>
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<div id='js-seed'>
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```js
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// Example
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var firstName = "Ada";
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var thirdToLastLetterOfFirstName = firstName[firstName.length - 3];
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// Setup
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var lastName = "Lovelace";
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// Only change code below this line
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var secondToLastLetterOfLastName = lastName;
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```
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</div>
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### After Test
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<div id='js-teardown'>
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```js
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(function(v){return v;})(secondToLastLetterOfLastName);
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```
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</div>
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</section>
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## Solution
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<section id='solution'>
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```js
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var firstName = "Ada";
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var thirdToLastLetterOfFirstName = firstName[firstName.length - 3];
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var lastName = "Lovelace";
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var secondToLastLetterOfLastName = lastName[lastName.length - 2];
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```
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</section>
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