# Prepend a line number to each line of a text document

Number lines from 1, right-aligned to two characters.

Canonical: https://1loc.dev/string/prepend-a-line-number-to-each-line-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 prependNumbers(text) { return text.split(/\r?\n/).map((line, i) => `${String(i + 1).padStart(2, ' ')} ${line}`).join('\n'); }
```

## Input

```json
"alpha\nbeta"
```

## Expected output

```json
" 1 alpha\n 2 beta"
```

## Edge case

Input:
```json
""
```
Output:
```json
" 1 "
```

## Limits

- Numbers above 99 widen the gutter. An empty text is one empty line.

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/prepend-a-line-number-to-each-line-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 contract, edge case and limits. Original MDX retained as inert source evidence.