2021-05-05 10:13:49 -07:00
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---
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id: bd7123c9c549eddfaeb5bdef
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title: 使用方括號查找字符串中的第一個字符
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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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dashedName: use-bracket-notation-to-find-the-first-character-in-a-string
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---
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# --description--
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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。
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2021-05-10 01:12:02 +05:30
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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。
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2021-05-05 10:13:49 -07:00
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2021-11-06 08:56:52 -07:00
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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。
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示例:
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```js
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const firstName = "Charles";
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const firstLetter = firstName[0];
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```
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`firstLetter` 值爲字符串 `C` 。
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# --instructions--
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使用方括號獲取變量 `lastName` 中的第一個字符,並賦給變量 `firstLetterOfLastName`。
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**提示:** 如果卡住了,請嘗試查看上面的示例。
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# --hints--
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`firstLetterOfLastName` 變量值應該爲 `L` 。
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```js
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assert(firstLetterOfLastName === 'L');
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```
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應該使用方括號表示法。
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```js
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2022-03-23 19:52:04 +05:30
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assert(code.match(/firstLetterOfLastName\s*=\s*lastName\s*\[\s*\d\s*\]/));
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```
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# --seed--
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## --after-user-code--
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```js
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(function(v){return v;})(firstLetterOfLastName);
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```
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## --seed-contents--
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```js
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// Setup
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let firstLetterOfLastName = "";
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const lastName = "Lovelace";
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// Only change code below this line
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firstLetterOfLastName = lastName; // Change this line
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```
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# --solutions--
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```js
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let firstLetterOfLastName = "";
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const 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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