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freeCodeCamp/curriculum/challenges/chinese/02-javascript-algorithms-and-data-structures/basic-javascript/use-bracket-notation-to-find-the-first-character-in-a-string.md
2022-03-23 15:22:04 +01:00

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---
id: bd7123c9c549eddfaeb5bdef
title: 使用方括号查找字符串中的第一个字符
challengeType: 1
videoUrl: 'https://scrimba.com/c/ca8JwhW'
forumTopicId: 18341
dashedName: use-bracket-notation-to-find-the-first-character-in-a-string
---
# --description--
方括号表示法(<dfn>Bracket notation</dfn>)是一种在字符串中的特定 index索引处获取字符的方法。
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。 这被称为基于零(<dfn>Zero-based</dfn>)的索引。
例如,单词 `Charles` 的索引 0 的字符是 `C`。 所以如果 `const firstName = "Charles"`,你可以通过 `firstName[0]` 得到字符串第一个字母的值。
示例:
```js
const firstName = "Charles";
const firstLetter = firstName[0];
```
`firstLetter` 值为字符串 `C`
# --instructions--
使用方括号获取变量 `lastName` 中的第一个字符,并赋给变量 `firstLetterOfLastName`
**提示:** 如果卡住了,请尝试查看上面的示例。
# --hints--
`firstLetterOfLastName` 变量值应该为 `L`
```js
assert(firstLetterOfLastName === 'L');
```
应该使用方括号表示法。
```js
assert(code.match(/firstLetterOfLastName\s*=\s*lastName\s*\[\s*\d\s*\]/));
```
# --seed--
## --after-user-code--
```js
(function(v){return v;})(firstLetterOfLastName);
```
## --seed-contents--
```js
// Setup
let firstLetterOfLastName = "";
const lastName = "Lovelace";
// Only change code below this line
firstLetterOfLastName = lastName; // Change this line
```
# --solutions--
```js
let firstLetterOfLastName = "";
const lastName = "Lovelace";
// Only change code below this line
firstLetterOfLastName = lastName[0];
```