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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. Markdown · 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 with a plain require()-able CommonJS entry is 1.1.0, published Jan 7, 2018; it declares support for Node.js *.

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

What to do

  1. On Node.js 20.19+, 22.12+ and newer, require("assertion-error") 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 assertionError = await import("assertion-error"). That works on every Node.js version the package supports (>=12).
  3. If you need a synchronous require() or run Node.js 18: npm install assertion-error@1.1.0, the last CommonJS release (published Jan 7, 2018); it declares Node.js *.
  4. TypeScript: types are bundled; install nothing extra.
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 1.4.0✓ works✓ works

How to import assertion-error

ES modules (import)

import * as assertionError from "assertion-error";

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 assertionError = require("assertion-error");

// Any Node.js version the package supports (>=12), from an async function:
async function main() {
  const assertionError = await import("assertion-error");
}

// Or pin the last CommonJS release (declares Node.js *):
// 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, corrected where a runtime test of that version contradicted them (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 with a plain require()-able CommonJS entry is 1.1.0, published Jan 7, 2018; it declares support for Node.js *.

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

1.1.0 is the last version of assertion-error with a CommonJS build; it declares Node.js *. 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?

From a CommonJS file, use a dynamic import inside an async function: const assertionError = await import("assertion-error"). That works on every Node.js version the package supports (>=12). On Node.js 20.19+, 22.12+ and newer, require("assertion-error") works with the latest version: Node.js loads synchronous ES modules through require(). Verified on Node.js 20, 22, 24 and 26. Alternatively pin assertion-error@1.1.0 (declares Node.js *).

Does assertion-error work in Bun?

Yes. import "assertion-error" loaded successfully in Bun 1.4.0 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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