25 lines
826 B
Markdown
25 lines
826 B
Markdown
---
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title: swapCase
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tags: string,beginner
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firstSeen: 2020-11-15T13:09:03+02:00
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lastUpdated: 2020-11-15T13:09:03+02:00
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---
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Creates a string with uppercase characters converted to lowercase and vice versa.
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- Use the spread operator (`...`) to convert `str` into an array of characters.
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- Use `String.prototype.toLowerCase()` and `String.prototype.toUpperCase()` to convert lowercase characters to uppercase and vice versa.
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- Use `Array.prototype.map()` to apply the transformation to each character, `Array.prototype.join()` to combine back into a string.
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- Note that it is not necessarily true that `swapCase(swapCase(str)) === str`.
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```js
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const swapCase = str =>
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[...str]
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.map(c => (c === c.toLowerCase() ? c.toUpperCase() : c.toLowerCase()))
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.join('');
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```
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```js
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swapCase('Hello world!'); // 'hELLO WORLD!'
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```
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