freeCodeCamp/curriculum/challenges/chinese/02-javascript-algorithms-and-data-structures/basic-javascript/use-bracket-notation-to-find-the-nth-character-in-a-string.md

---
id: bd7123c9c450eddfaeb5bdef
challengeType: 1
videoUrl: 'https://scrimba.com/c/cWPVJua'
forumTopicId: 18343
localeTitle: 使用方括号查找字符串中的第N个字符
---

## Description
<section id='description'>
你也可以使用方括号来获得一个字符串中的其他位置的字符。
请记住，程序是从<code>0</code>开始计数，所以获取第一个字符实际上是[0]。
</section>

## Instructions
<section id='instructions'>
让我们使用方括号，把<code>lastName</code>变量的第三个字符赋值给<code>thirdLetterOfLastName</code>。
<strong>提示</strong><br>如果你遇到困难了，看看<code>secondLetterOfFirstName</code>变量是如何做的。
</section>

## Tests
<section id='tests'>

```yml
tests:
  - text: <code>thirdLetterOfLastName</code>的值应该是<code>v</code>。
    testString: assert(thirdLetterOfLastName === 'v');
  - text: 你应该使用方括号。
    testString: assert(code.match(/thirdLetterOfLastName\s*?=\s*?lastName\[.*?\]/));

```

</section>

## Challenge Seed
<section id='challengeSeed'>

<div id='js-seed'>

```js
// Example
var firstName = "Ada";
var secondLetterOfFirstName = firstName[1];

// Setup
var lastName = "Lovelace";

// Only change code below this line.
var thirdLetterOfLastName = lastName;


```

</div>


### After Test
<div id='js-teardown'>

```js
(function(v){return v;})(thirdLetterOfLastName);
```

</div>

</section>

## Solution
<section id='solution'>


```js
var lastName = "Lovelace";
var thirdLetterOfLastName = lastName[2];
```

</section>