# Get the file extension from a file name

Return the text after the last dot, or an empty string.

Canonical: https://1loc.dev/string/get-the-file-extension-from-a-file-name/
Version: 1.0.0
Runtime: JavaScript · Node.js 22 / modern browsers
Verification: Local fixtures; no external services
Updated: 2026-10-28

## Implementation

```javascript
function fileExtension(name) { const dot = name.lastIndexOf('.'); return dot > 0 ? name.slice(dot + 1) : ''; }
```

## Input

```json
"invoice-8812.pdf"
```

## Expected output

```json
"pdf"
```

## Edge case

Input:
```json
".env"
```
Output:
```json
""
```

## Limits

- The original returned the whole name when there was no dot. A leading dot marks a hidden file, not an extension.
- Only the last part is returned: archive.tar.gz gives gz.

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/get-the-file-extension-from-a-file-name.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: Returns an empty string when there is no extension or only a leading dot; the original returned the whole name. Original MDX retained as inert source evidence.