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

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

ESM-only ESM-only since 3.0.0 — last CommonJS version is 2.2.0

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.
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

Does is-wsl@3.1.1 actually load? Runtime test results

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

Runtimerequire("is-wsl")import "is-wsl"
Node.js 18✗ failsERR_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 (import)

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 (require)

// 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, corrected where a runtime test of that version contradicted them (9 versions; the newest 9 shown).

VersionsFormatFirst published
3.0.0 – 3.1.1ESM-onlyAug 8, 2023
1.0.0 – 2.2.0CommonJSApr 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

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