# Flatten a nested array

Turn a nested array into one sequence of values.

Canonical: https://1loc.dev/array/flatten-an-array/
Version: 1.0.0
Runtime: JavaScript · Node.js 22 / modern browsers
Verification: Local fixtures; no external services
Updated: 2026-10-28

## Implementation

```javascript
function flatten(values) { return values.flat(Infinity); }
```

## Input

```json
[
  1,
  [
    2,
    [
      3
    ]
  ],
  4
]
```

## Expected output

```json
[
  1,
  2,
  3,
  4
]
```

## Edge case

Input:
```json
[
  [],
  [
    1,
    []
  ]
]
```
Output:
```json
[
  1
]
```

## Limits

- Input depth is capped at 12 and the total element count at 1,000 in this lab.
- Array holes are skipped. JSON input cannot represent holes.

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/flatten-an-array.mdx
Source file (this edition): https://github.com/akamind/1loc/blob/0a77f131b22d2ba3b7ec1728846f900c22821678/contents/flatten-an-array.mdx
Author: Nguyen Huu Phuoc and original contributors
Contributors: nico2che
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.