# Is assert ESM-only? Can you require() it?

> assert@2.1.0 is a CommonJS package. CommonJS — require() works on every Node.js version we test.

The assert module from Node.js, for the browser.

Last verified Sep 9, 2026 against assert@2.1.0.

assert ships CommonJS only. require("assert") works on every Node.js version we test (18, 20, 22, 24 and 26) and in Bun. import "assert" also works because Node.js and Bun can import CommonJS from ES modules, but only the default export is guaranteed; named imports depend on Node's static analysis of the module.

## What to do

1. require("assert") works on every Node.js version we test (18, 20, 22, 24 and 26) and in Bun.
2. From ES modules use the default import: import assert from "assert"; then destructure. Named imports only work when Node.js can statically detect the exports.
3. TypeScript: npm install -D @types/assert

## Facts

- Latest: 2.1.0 (Sep 7, 2023)
- Module format: CommonJS
- Last CommonJS version: 2.1.0
- TypeScript types: @types/assert
- Node engines: not declared
- Weekly downloads: 16.1M
- License: MIT

## Runtime test results for assert@2.1.0

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

| Runtime | require("assert") | import "assert" |
|---|---|---|
| Node.js 18 | works | 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 assert

ES modules:

```js
import assert from "assert";
```

CommonJS:

```js
const assert = require("assert");
```

## Module format by version

Derived from the type, main and exports fields of every stable release on npm (16 versions; the newest 16 shown).

| Versions | Format | First published |
|---|---|---|
| 0.4.9 – 2.1.0 | CommonJS | Jun 30, 2011 |

## Frequently asked

**Is assert ESM-only?**

assert@2.1.0 is a CommonJS package. assert ships CommonJS only. require("assert") works on every Node.js version we test (18, 20, 22, 24 and 26) and in Bun. import "assert" also works because Node.js and Bun can import CommonJS from ES modules, but only the default export is guaranteed; named imports depend on Node's static analysis of the module.

**Can I import assert with ES module syntax?**

Yes. import assert from "assert" works in Node.js and Bun because they support importing CommonJS modules. Named imports work only when Node.js can statically detect the exports.

**Does assert work in Bun?**

Yes. import "assert" loaded successfully in Bun 1.4.0 on Sep 9, 2026.

**Does assert ship TypeScript types?**

Not bundled. Install the community types with "npm install -D @types/assert".

## Links

- [assert on npm](https://www.npmjs.com/package/assert)
- [Source repository](https://github.com/browserify/commonjs-assert)
- [HTML version](https://canirequire.com/package/assert/)
- [JSON version](https://canirequire.com/package/assert.json)

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