# Swap case of characters in a string

Uppercase lowercase letters and lowercase the rest.

Canonical: https://1loc.dev/string/swap-case-of-characters-in-a-string/
Version: 1.0.0
Runtime: JavaScript · Node.js 22 / modern browsers
Verification: Local fixtures; no external services
Updated: 2026-10-28

## Implementation

```javascript
function swapCase(text) { return Array.from(text).map(char => char === char.toLowerCase() ? char.toUpperCase() : char.toLowerCase()).join(''); }
```

## Input

```json
"Hello World"
```

## Expected output

```json
"hELLO wORLD"
```

## Edge case

Input:
```json
"ß"
```
Output:
```json
"SS"
```

## Limits

- Case mapping can change length: ß uppercases to SS.

The lab validates types and size before calling this function. Add equivalent validation at your own trust boundary.

## Source and license

Original: https://github.com/phuocng/1loc/blob/14b481cf60dff1620ab1bb99a43b1f68068cdd9b/contents/swap-case-of-characters-in-a-string.mdx
Author: Nguyen Huu Phuoc and original contributors
Contributors: See original repository history
Source commit: 14b481cf60dff1620ab1bb99a43b1f68068cdd9b
Copyright (c) 2020 phuoc-ng
License: MIT — https://1loc.dev/licenses/
Maintainer: Oveyon
Modifications: Iterates code points instead of UTF-16 units. Original MDX retained as inert source evidence.