# Is array-union ESM-only? Can you require() it?

> array-union@3.0.1 is ESM-only. ESM-only since 3.0.0 — last CommonJS version is 2.1.0.

Create an array of unique values, in order, from the input arrays

Last verified Sep 9, 2026 against array-union@3.0.1.

array-union dropped its CommonJS build in 3.0.0 (March 2021). The last version with a plain require()-able CommonJS entry is 2.1.0, published Apr 22, 2019; it declares support for Node.js >=8.

On Node.js 20.19+, 22.12+ and newer, require("array-union") works with the latest version: Node.js loads synchronous ES modules through require(). Verified on Node.js 20, 22, 24 and 26. On Node.js 18, which has no require(esm), require("array-union") fails with ERR_REQUIRE_ESM.

## What to do

1. On Node.js 20.19+, 22.12+ and newer, require("array-union") works with the latest version: Node.js loads synchronous ES modules through require(). Verified on Node.js 20, 22, 24 and 26.
2. From a CommonJS file, use a dynamic import inside an async function: const arrayUnion = await import("array-union"). That works on every Node.js version the package supports (>=12).
3. If you need a synchronous require() or run Node.js 18: npm install array-union@2.1.0, the last CommonJS release (published Apr 22, 2019); it declares Node.js >=8.
4. TypeScript: no types are available for array-union; declare the module yourself if you need them.

## Facts

- Latest: 3.0.1 (Mar 1, 2021)
- Module format: ESM-only
- Last CommonJS version: 2.1.0
- ESM-only since: 3.0.0 (Mar 1, 2021)
- TypeScript types: none
- Node engines: >=12
- Weekly downloads: 31.3M
- License: MIT

## Runtime test results for array-union@3.0.1

Installed and executed on Sep 9, 2026 with require("array-union") from a CommonJS file and import "array-union" from an ES module.

| Runtime | require("array-union") | import "array-union" |
|---|---|---|
| Node.js 18 | fails (ERR_REQUIRE_ESM) | works |
| Node.js 20 | works | works |
| Node.js 22 | works | works |
| Node.js 24 | works | works |
| Node.js 26 | works | works |
| Bun 1.4.0 | works | works |

## How to import array-union

ES modules:

```js
import * as arrayUnion from "array-union";
```

Namespace import shown because the ESM entry may have no default export; use named imports for what it exports.

CommonJS:

```js
// Node.js 20.19+, 22.12+ and newer (verified):
const arrayUnion = require("array-union");

// Any Node.js version the package supports (>=12), from an async function:
async function main() {
  const arrayUnion = await import("array-union");
}

// Or pin the last CommonJS release (declares Node.js >=8):
// npm install array-union@2.1.0
```

## Module format by version

Derived from the type, main and exports fields of every stable release on npm (8 versions; the newest 8 shown).

| Versions | Format | First published |
|---|---|---|
| 3.0.0 – 3.0.1 | ESM-only | Mar 1, 2021 |
| 0.1.0 – 2.1.0 | CommonJS | Jun 19, 2014 |

## Frequently asked

**Is array-union ESM-only?**

array-union@3.0.1 is ESM-only. array-union dropped its CommonJS build in 3.0.0 (March 2021). The last version with a plain require()-able CommonJS entry is 2.1.0, published Apr 22, 2019; it declares support for Node.js >=8.

**Which version of array-union still supports CommonJS / require()?**

2.1.0 is the last version of array-union with a CommonJS build; it declares Node.js >=8. Install it with "npm install array-union@2.1.0". Every version from 3.0.0 on is ESM-only.

**How do I use array-union from a CommonJS file?**

From a CommonJS file, use a dynamic import inside an async function: const arrayUnion = await import("array-union"). That works on every Node.js version the package supports (>=12). On Node.js 20.19+, 22.12+ and newer, require("array-union") works with the latest version: Node.js loads synchronous ES modules through require(). Verified on Node.js 20, 22, 24 and 26. Alternatively pin array-union@2.1.0 (declares Node.js >=8).

**Does array-union work in Bun?**

Yes. import "array-union" loaded successfully in Bun 1.4.0 on Sep 9, 2026.

**Does array-union ship TypeScript types?**

No. array-union ships no type declarations and there is no @types package for it.

## Links

- [array-union on npm](https://www.npmjs.com/package/array-union)
- [Source repository](https://github.com/sindresorhus/array-union)
- [HTML version](https://canirequire.com/package/array-union/)
- [JSON version](https://canirequire.com/package/array-union.json)

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