# Remove duplicate values

Keep the first occurrence of each value, in its original order.

Canonical: https://1loc.dev/array/remove-duplicate-values-in-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 unique(values) { return [...new Set(values)]; }
```

## Input

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

## Expected output

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

## Edge case

Input:
```json
[
  {
    "id": 1
  },
  {
    "id": 1
  }
]
```
Output:
```json
[
  {
    "id": 1
  },
  {
    "id": 1
  }
]
```

## Limits

- Set compares objects by reference. Two separately created objects are not duplicates.
- Values use SameValueZero equality; this is not deep deduplication.

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/remove-duplicate-values-in-an-array.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 bounds, edge cases, local fixtures and rebuilt presentation. Original MDX retained as inert source evidence.