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Is assertion-error ESM-only? Can you require() it?

Error constructor for test and validation frameworks that implements standardized AssertionError specification.

Last verified Sep 9, 2026 against assertion-error@2.0.1. JSON

ESM-only ESM-only since 2.0.0 — last CommonJS version is 1.1.0

assertion-error dropped its CommonJS build in 2.0.0 (October 2021). The last version you can require() on every Node.js version, including 18 and older, is 1.1.0, published Jan 7, 2018.

On Node.js 20.19+, 22.12+ and every newer release, require("assertion-error") 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
2.0.1 (Oct 18, 2023)
Module format
ESM-only
Last CommonJS version
1.1.0
ESM-only since
2.0.0 (Oct 5, 2021)
TypeScript types
Bundled
Node engines
>=12
Weekly downloads
89.6M
License
MIT

Does assertion-error@2.0.1 actually load? Runtime test results

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

Runtimerequire("assertion-error")import "assertion-error"
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 assertion-error

ES modules (import)

import assertionError from "assertion-error";

CommonJS (require)

// Node.js 20.19+ / 22.12+ / newer (package has no top-level await):
const assertionError = require("assertion-error");

// Any Node.js version:
const assertionError = await import("assertion-error");

// Or pin the last CommonJS release:
// npm install assertion-error@1.1.0

Module format by version

Derived from the type, main and exports fields of every stable release on npm (7 versions; the newest 7 shown).

VersionsFormatFirst published
2.0.0 – 2.0.1ESM-onlyOct 5, 2021
0.1.0 – 1.1.0CommonJSApr 7, 2013

Frequently asked

Is assertion-error ESM-only?

assertion-error@2.0.1 is ESM-only. assertion-error dropped its CommonJS build in 2.0.0 (October 2021). The last version you can require() on every Node.js version, including 18 and older, is 1.1.0, published Jan 7, 2018.

Which version of assertion-error still supports CommonJS / require()?

1.1.0 is the last version of assertion-error with a CommonJS build. Install it with "npm install assertion-error@1.1.0". Every version from 2.0.0 on is ESM-only.

How do I use assertion-error from a CommonJS file?

Use a dynamic import: const mod = await import("assertion-error"). On Node.js 20.19+, 22.12+ and newer, a plain require("assertion-error") also works for ESM packages that do not use top-level await. Alternatively pin assertion-error@1.1.0.

Does assertion-error work in Bun?

Yes. import "assertion-error" loaded successfully in Bun 1.4 on Sep 9, 2026.

Does assertion-error ship TypeScript types?

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

Links

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