# Is is-wsl ESM-only? Can you require() it?

> is-wsl@3.1.1 is ESM-only. ESM-only since 3.0.0 — last CommonJS version is 2.2.0.

Check if the process is running inside Windows Subsystem for Linux (Bash on Windows)

Last verified Sep 9, 2026 against is-wsl@3.1.1.

is-wsl dropped its CommonJS build in 3.0.0 (August 2023). The last version with a plain require()-able CommonJS entry is 2.2.0, published May 3, 2020; it declares support for Node.js >=8.

On Node.js 20.19+, 22.12+ and newer, require("is-wsl") 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("is-wsl") fails with ERR_REQUIRE_ESM.

## What to do

1. On Node.js 20.19+, 22.12+ and newer, require("is-wsl") 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 isWsl = await import("is-wsl"). That works on every Node.js version the package supports (>=16).
3. If you need a synchronous require() or run Node.js 18: npm install is-wsl@2.2.0, the last CommonJS release (published May 3, 2020); it declares Node.js >=8.
4. TypeScript: types are bundled; install nothing extra.

## Facts

- Latest: 3.1.1 (Feb 15, 2026)
- Module format: ESM-only
- Last CommonJS version: 2.2.0
- ESM-only since: 3.0.0 (Aug 8, 2023)
- TypeScript types: bundled
- Node engines: >=16
- Weekly downloads: 117.6M
- License: MIT

## Runtime test results for is-wsl@3.1.1

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

| Runtime | require("is-wsl") | import "is-wsl" |
|---|---|---|
| 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 is-wsl

ES modules:

```js
import * as isWsl from "is-wsl";
```

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 isWsl = require("is-wsl");

// Any Node.js version the package supports (>=16), from an async function:
async function main() {
  const isWsl = await import("is-wsl");
}

// Or pin the last CommonJS release (declares Node.js >=8):
// npm install is-wsl@2.2.0
```

## Module format by version

Derived from the type, main and exports fields of every stable release on npm (9 versions; the newest 9 shown).

| Versions | Format | First published |
|---|---|---|
| 3.0.0 – 3.1.1 | ESM-only | Aug 8, 2023 |
| 1.0.0 – 2.2.0 | CommonJS | Apr 16, 2017 |

## Frequently asked

**Is is-wsl ESM-only?**

is-wsl@3.1.1 is ESM-only. is-wsl dropped its CommonJS build in 3.0.0 (August 2023). The last version with a plain require()-able CommonJS entry is 2.2.0, published May 3, 2020; it declares support for Node.js >=8.

**Which version of is-wsl still supports CommonJS / require()?**

2.2.0 is the last version of is-wsl with a CommonJS build; it declares Node.js >=8. Install it with "npm install is-wsl@2.2.0". Every version from 3.0.0 on is ESM-only.

**How do I use is-wsl from a CommonJS file?**

From a CommonJS file, use a dynamic import inside an async function: const isWsl = await import("is-wsl"). That works on every Node.js version the package supports (>=16). On Node.js 20.19+, 22.12+ and newer, require("is-wsl") works with the latest version: Node.js loads synchronous ES modules through require(). Verified on Node.js 20, 22, 24 and 26. Alternatively pin is-wsl@2.2.0 (declares Node.js >=8).

**Does is-wsl work in Bun?**

Yes. import "is-wsl" loaded successfully in Bun 1.4.0 on Sep 9, 2026.

**Does is-wsl ship TypeScript types?**

Yes. is-wsl bundles its own type declarations; no @types package is needed.

## Links

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

---

For scripts and AI agents: any package is at https://canirequire.com/package/<name>/index.md (Markdown) or https://canirequire.com/package/<name>.json (JSON); the site index is https://canirequire.com/llms.txt. Fetch the URL directly; no search needed.