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

> internmap@2.0.3 is ESM-only. ESM-only since 2.0.0 — last CommonJS version is 1.0.1.

Map and Set with automatic key interning

Last verified Sep 9, 2026 against internmap@2.0.3.

internmap dropped its CommonJS build in 2.0.0 (June 2021). The last version with a plain require()-able CommonJS entry is 1.0.1, published Mar 10, 2021.

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

## What to do

1. On Node.js 20.19+, 22.12+ and newer, require("internmap") 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 internmap = await import("internmap"). 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 internmap@1.0.1, the last CommonJS release (published Mar 10, 2021).
4. TypeScript: no types are available for internmap; declare the module yourself if you need them.

## Facts

- Latest: 2.0.3 (Sep 20, 2021)
- Module format: ESM-only
- Last CommonJS version: 1.0.1
- ESM-only since: 2.0.0 (Jun 3, 2021)
- TypeScript types: none
- Node engines: >=12
- Weekly downloads: 79.5M
- License: ISC

## Runtime test results for internmap@2.0.3

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

| Runtime | require("internmap") | import "internmap" |
|---|---|---|
| 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 internmap

ES modules:

```js
import * as internmap from "internmap";
```

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 internmap = require("internmap");

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

// Or pin the last CommonJS release:
// npm install internmap@1.0.1
```

## Module format by version

Derived from the type, main and exports fields of every stable release on npm (6 versions; the newest 6 shown).

| Versions | Format | First published |
|---|---|---|
| 2.0.0 – 2.0.3 | ESM-only | Jun 3, 2021 |
| 1.0.0 – 1.0.1 | CommonJS | Jan 21, 2021 |

## Frequently asked

**Is internmap ESM-only?**

internmap@2.0.3 is ESM-only. internmap dropped its CommonJS build in 2.0.0 (June 2021). The last version with a plain require()-able CommonJS entry is 1.0.1, published Mar 10, 2021.

**Which version of internmap still supports CommonJS / require()?**

1.0.1 is the last version of internmap with a CommonJS build. Install it with "npm install internmap@1.0.1". Every version from 2.0.0 on is ESM-only.

**How do I use internmap from a CommonJS file?**

From a CommonJS file, use a dynamic import inside an async function: const internmap = await import("internmap"). That works on every Node.js version the package supports (>=12). On Node.js 20.19+, 22.12+ and newer, require("internmap") works with the latest version: Node.js loads synchronous ES modules through require(). Verified on Node.js 20, 22, 24 and 26. Alternatively pin internmap@1.0.1.

**Does internmap work in Bun?**

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

**Does internmap ship TypeScript types?**

No. internmap ships no type declarations and there is no @types package for it.

## Links

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

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