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freeCodeCamp/curriculum/challenges/chinese-traditional/02-javascript-algorithms-and-data-structures/basic-javascript/use-bracket-notation-to-find-the-first-character-in-a-string.md
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---
id: bd7123c9c549eddfaeb5bdef
title: 使用方括號查找字符串中的第一個字符
challengeType: 1
videoUrl: 'https://scrimba.com/c/ca8JwhW'
forumTopicId: 18341
dashedName: use-bracket-notation-to-find-the-first-character-in-a-string
---
# --description--
方括號表示法(<dfn>Bracket notation</dfn>)是一種在字符串中的特定 index索引處獲取字符的方法。
大多數現代編程語言,如 JavaScript不同於人類從 1 開始計數。 它們是從 0 開始計數。 這被稱爲基於零(<dfn>Zero-based</dfn>)的索引。
例如,單詞 `Charles` 的索引 0 的字符是 `C`。 所以如果 `const firstName = "Charles"`,你可以通過 `firstName[0]` 得到字符串第一個字母的值。
示例:
```js
const firstName = "Charles";
const firstLetter = firstName[0];
```
`firstLetter` 值爲字符串 `C`
# --instructions--
使用方括號獲取變量 `lastName` 中的第一個字符,並賦給變量 `firstLetterOfLastName`
**提示:** 如果卡住了,請嘗試查看上面的示例。
# --hints--
`firstLetterOfLastName` 變量值應該爲 `L`
```js
assert(firstLetterOfLastName === 'L');
```
應該使用方括號表示法。
```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];
```