# Merge two arrays

Concatenate two arrays, optionally dropping duplicates.

Canonical: https://1loc.dev/array/merge-two-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 merge({ a, b, unique = false }) { return unique ? [...new Set([...a, ...b])] : [...a, ...b]; }
```

## Input

```json
{
  "a": [
    "ana@example.com"
  ],
  "b": [
    "rui@example.com",
    "ana@example.com"
  ]
}
```

## Expected output

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

## Edge case

Input:
```json
{
  "a": [
    "ana@example.com"
  ],
  "b": [
    "rui@example.com",
    "ana@example.com"
  ],
  "unique": true
}
```
Output:
```json
[
  "ana@example.com",
  "rui@example.com"
]
```

## Limits

- The original page showed both versions; unique selects one.

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/merge-two-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: Combines the two original variants behind a unique option. Original MDX retained as inert source evidence.