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

Check if something is a Node.js stream

Last verified Sep 9, 2026 against is-stream@4.0.1. Markdown · JSON

ESM-only ESM-only since 3.0.0 — last CommonJS version is 2.0.1

is-stream dropped its CommonJS build in 3.0.0 (August 2021). The last version with a plain require()-able CommonJS entry is 2.0.1, published Jul 26, 2021; it declares support for Node.js >=8.

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

What to do

  1. On Node.js 20.19+, 22.12+ and newer, require("is-stream") 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 isStream = await import("is-stream"). That works on every Node.js version the package supports (>=18).
  3. If you need a synchronous require() or run Node.js 18: npm install is-stream@2.0.1, the last CommonJS release (published Jul 26, 2021); it declares Node.js >=8.
  4. TypeScript: types are bundled; install nothing extra.
Latest
4.0.1 (Feb 19, 2024)
Module format
ESM-only
Last CommonJS version
2.0.1
ESM-only since
3.0.0 (Aug 10, 2021)
TypeScript types
Bundled
Node engines
>=18
Weekly downloads
142.3M
License
MIT

Does is-stream@4.0.1 actually load? Runtime test results

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

Runtimerequire("is-stream")import "is-stream"
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-stream

ES modules (import)

import * as isStream from "is-stream";

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 isStream = require("is-stream");

// Any Node.js version the package supports (>=18), from an async function:
async function main() {
  const isStream = await import("is-stream");
}

// Or pin the last CommonJS release (declares Node.js >=8):
// npm install is-stream@2.0.1

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 (8 versions; the newest 8 shown).

VersionsFormatFirst published
3.0.0 – 4.0.1ESM-onlyAug 10, 2021
1.0.0 – 2.0.1CommonJSJan 18, 2015

Frequently asked

Is is-stream ESM-only?

is-stream@4.0.1 is ESM-only. is-stream dropped its CommonJS build in 3.0.0 (August 2021). The last version with a plain require()-able CommonJS entry is 2.0.1, published Jul 26, 2021; it declares support for Node.js >=8.

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

2.0.1 is the last version of is-stream with a CommonJS build; it declares Node.js >=8. Install it with "npm install is-stream@2.0.1". Every version from 3.0.0 on is ESM-only.

How do I use is-stream from a CommonJS file?

From a CommonJS file, use a dynamic import inside an async function: const isStream = await import("is-stream"). That works on every Node.js version the package supports (>=18). On Node.js 20.19+, 22.12+ and newer, require("is-stream") 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-stream@2.0.1 (declares Node.js >=8).

Does is-stream work in Bun?

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

Does is-stream ship TypeScript types?

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

Links

Other esm-only packages

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