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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. 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 you can require() on every Node.js version, including 18 and older, is 2.0.1, published Jul 26, 2021.

On Node.js 20.19+, 22.12+ and every newer release, require("is-stream") works anyway: Node can load synchronous ES modules through require(). Verified on Node 20, 22, 24, 26. Node.js 18 and older still fail with ERR_REQUIRE_ESM.

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✓ works✓ works

How to import is-stream

ES modules (import)

import isStream from "is-stream";

CommonJS (require)

// Node.js 20.19+ / 22.12+ / newer (package has no top-level await):
const isStream = require("is-stream");

// Any Node.js version:
const isStream = await import("is-stream");

// Or pin the last CommonJS release:
// 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 (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 you can require() on every Node.js version, including 18 and older, is 2.0.1, published Jul 26, 2021.

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

2.0.1 is the last version of is-stream with a CommonJS build. 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?

Use a dynamic import: const mod = await import("is-stream"). On Node.js 20.19+, 22.12+ and newer, a plain require("is-stream") also works for ESM packages that do not use top-level await. Alternatively pin is-stream@2.0.1.

Does is-stream work in Bun?

Yes. import "is-stream" loaded successfully in Bun 1.4 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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