---
title: allUnique
tags: array,beginner
---

Checks if all elements in an array are unique.

- Create a new `Set` from the mapped values to keep only unique occurrences.
- Use `Array.prototype.length` and `Set.prototype.size` to compare the length of the unique values to the original array.

```js
const allUnique = arr => arr.length === new Set(arr).size;
```

```js
allUnique([1, 2, 3, 4]); // true
allUnique([1, 1, 2, 3]); // false
```