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

> concat-map@0.0.2 is a CommonJS package. CommonJS — require() works on every Node.js version we test.

concatenative mapdashery

Last verified Sep 9, 2026 against concat-map@0.0.2.

concat-map ships CommonJS only. require("concat-map") works on every Node.js version we test (18, 20, 22, 24 and 26) and in Bun. import "concat-map" 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("concat-map") 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 concatMap from "concat-map"; then destructure. Named imports only work when Node.js can statically detect the exports.
3. TypeScript: npm install -D @types/concat-map

## Facts

- Latest: 0.0.2 (Oct 12, 2022)
- Module format: CommonJS
- Last CommonJS version: 0.0.2
- TypeScript types: @types/concat-map
- Node engines: not declared
- Weekly downloads: 80.0M
- License: MIT

## Runtime test results for concat-map@0.0.2

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

| Runtime | require("concat-map") | import "concat-map" |
|---|---|---|
| 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 concat-map

ES modules:

```js
import concatMap from "concat-map";
```

CommonJS:

```js
const concatMap = require("concat-map");
```

## Module format by version

Derived from the type, main and exports fields of every stable release on npm (3 versions; the newest 3 shown).

| Versions | Format | First published |
|---|---|---|
| 0.0.0 – 0.0.2 | CommonJS | Jun 8, 2012 |

## Frequently asked

**Is concat-map ESM-only?**

concat-map@0.0.2 is a CommonJS package. concat-map ships CommonJS only. require("concat-map") works on every Node.js version we test (18, 20, 22, 24 and 26) and in Bun. import "concat-map" 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 concat-map with ES module syntax?**

Yes. import concatMap from "concat-map" 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 concat-map work in Bun?**

Yes. import "concat-map" loaded successfully in Bun 1.4.0 on Sep 9, 2026.

**Does concat-map ship TypeScript types?**

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

## Links

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

---

For scripts and AI agents: any package is at https://canirequire.com/package/<name>/index.md (Markdown) or https://canirequire.com/package/<name>.json (JSON); the site index is https://canirequire.com/llms.txt. Fetch the URL directly; no search needed.