86 lines
2.0 KiB
Markdown
86 lines
2.0 KiB
Markdown
---
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id: bd7123c9c549eddfaeb5bdef
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title: Use Bracket Notation to Find the First Character in a String
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challengeType: 1
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videoUrl: 'https://scrimba.com/c/ca8JwhW'
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forumTopicId: 18341
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localeTitle: 使用方括号查找字符串中的第一个字符
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---
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## Description
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<section id='description'>
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方括号表示法是一种在字符串中的特定<code>index</code>（索引）处获取字符的方法。
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大多数现代编程语言，如JavaScript，不同于人类从 1 开始计数。它们是从 0 开始计数，这被称为 <dfn>基于零</dfn> 的索引。
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例如, 在单词 "Charles" 中索引 0 上的字符为 "C"，所以在<code>var firstName = "Charles"</code>中，你可以使用<code>firstName[0]</code>来获得第一个位置上的字符。
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</section>
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## Instructions
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<section id='instructions'>
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使用方括号获取变量<code>lastName</code>中的第一个字符，并赋给变量<code>firstLetterOfLastName</code>。
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<strong>提示</strong><br>如果你遇到困难了，不妨看看变量<code>firstLetterOfFirstName</code>是如何赋值的。
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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>firstLetterOfLastName</code>的值应该是<code>L</code>。
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testString: assert(firstLetterOfLastName === 'L');
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- text: 你应该使用中括号。
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testString: assert(code.match(/firstLetterOfLastName\s*?=\s*?lastName\[.*?\]/));
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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 firstLetterOfFirstName = "";
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var firstName = "Ada";
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firstLetterOfFirstName = firstName[0];
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// Setup
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var firstLetterOfLastName = "";
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var lastName = "Lovelace";
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// Only change code below this line
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firstLetterOfLastName = 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;})(firstLetterOfLastName);
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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 firstLetterOfLastName = "";
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var lastName = "Lovelace";
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// Only change code below this line
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firstLetterOfLastName = lastName[0];
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```
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</section>
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