# Remove duplicate lines

Keep the first occurrence of every exact line while normalizing CRLF to LF.

Canonical: https://1loc.dev/string/remove-duplicate-lines-of-a-text-document/
Version: 1.0.0
Runtime: JavaScript · Node.js 22 / modern browsers
Verification: Local fixtures; no external services
Updated: 2026-10-28

## Implementation

```javascript
function uniqueLines(value) { return [...new Set(value.split(/\r?\n/))].join('\n'); }
```

## Input

```json
"accepted\ndelivered\naccepted"
```

## Expected output

```json
"accepted\ndelivered"
```

## Edge case

Input:
```json
""
```
Output:
```json
""
```

## Limits

- Whitespace and case matter. One empty line is retained; line endings become LF.

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/remove-duplicate-lines-of-a-text-document.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: Curated implementation; explicit input bounds, edge cases, local fixtures and rebuilt presentation. Original MDX retained as inert source evidence.