# Get union of arrays

Merge arrays and keep each value once, in first-seen order.

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

## Implementation

```javascript
function union(arrays) { return [...new Set(arrays.flat())]; }
```

## Input

```json
[
  [
    "ana@example.com",
    "rui@example.com"
  ],
  [
    "rui@example.com",
    "lia@example.com"
  ]
]
```

## Expected output

```json
[
  "ana@example.com",
  "rui@example.com",
  "lia@example.com"
]
```

## Edge case

Input:
```json
[]
```
Output:
```json
[]
```

## Limits

- The original took the arrays as separate arguments; the lab passes one array of arrays.
- Values compare with SameValueZero.

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-union-of-arrays.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: Takes one array of arrays instead of rest arguments. Original MDX retained as inert source evidence.