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

> sinon-chai@4.0.1 is ESM-only. ESM-only since 4.0.0 — last CommonJS version is 3.7.0.

Extends Chai with assertions for the Sinon.JS mocking framework.

Last verified Sep 9, 2026 against sinon-chai@4.0.1.

sinon-chai dropped its CommonJS build in 4.0.0 (July 2024). The last version with a plain require()-able CommonJS entry is 3.7.0, published May 25, 2021.

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

## What to do

1. On Node.js 20.19+, 22.12+ and newer, require("sinon-chai") 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 sinonChai = await import("sinon-chai"). That works on every Node.js version the package supports.
3. If you need a synchronous require() or run Node.js 18: npm install sinon-chai@3.7.0, the last CommonJS release (published May 25, 2021).
4. TypeScript: npm install -D @types/sinon-chai

## Facts

- Latest: 4.0.1 (Aug 22, 2025)
- Module format: ESM-only
- Last CommonJS version: 3.7.0
- ESM-only since: 4.0.0 (Jul 25, 2024)
- TypeScript types: @types/sinon-chai
- Node engines: not declared
- Weekly downloads: 835K
- License: (BSD-2-Clause OR WTFPL)

## Runtime test results for sinon-chai@4.0.1

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

| Runtime | require("sinon-chai") | import "sinon-chai" |
|---|---|---|
| Node.js 18 | fails (ERR_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 sinon-chai

ES modules:

```js
import * as sinonChai from "sinon-chai";
```

Namespace import shown because the ESM entry may have no default export; use named imports for what it exports.

CommonJS:

```js
// Node.js 20.19+, 22.12+ and newer (verified):
const sinonChai = require("sinon-chai");

// Any Node.js version the package supports, from an async function:
async function main() {
  const sinonChai = await import("sinon-chai");
}

// Or pin the last CommonJS release:
// npm install sinon-chai@3.7.0
```

## Module format by version

Derived from the type, main and exports fields of every stable release on npm (36 versions; the newest 36 shown).

| Versions | Format | First published |
|---|---|---|
| 4.0.0 – 4.0.1 | ESM-only | Jul 25, 2024 |
| 1.0.0 – 3.7.0 | CommonJS | Feb 13, 2012 |

## Frequently asked

**Is sinon-chai ESM-only?**

sinon-chai@4.0.1 is ESM-only. sinon-chai dropped its CommonJS build in 4.0.0 (July 2024). The last version with a plain require()-able CommonJS entry is 3.7.0, published May 25, 2021.

**Which version of sinon-chai still supports CommonJS / require()?**

3.7.0 is the last version of sinon-chai with a CommonJS build. Install it with "npm install sinon-chai@3.7.0". Every version from 4.0.0 on is ESM-only.

**How do I use sinon-chai from a CommonJS file?**

From a CommonJS file, use a dynamic import inside an async function: const sinonChai = await import("sinon-chai"). That works on every Node.js version the package supports. On Node.js 20.19+, 22.12+ and newer, require("sinon-chai") works with the latest version: Node.js loads synchronous ES modules through require(). Verified on Node.js 20, 22, 24 and 26. Alternatively pin sinon-chai@3.7.0.

**Does sinon-chai work in Bun?**

Yes. import "sinon-chai" loaded successfully in Bun 1.4.0 on Sep 9, 2026.

**Does sinon-chai ship TypeScript types?**

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

## Links

- [sinon-chai on npm](https://www.npmjs.com/package/sinon-chai)
- [Source repository](https://github.com/chaijs/sinon-chai)
- [HTML version](https://canirequire.com/package/sinon-chai/)
- [JSON version](https://canirequire.com/package/sinon-chai.json)

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