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

> concat-stream@2.0.0 is a CommonJS package. CommonJS — require() works on every Node.js version we test.

writable stream that concatenates strings or binary data and calls a callback with the result

Last verified Sep 9, 2026 against concat-stream@2.0.0.

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

## Facts

- Latest: 2.0.0 (Dec 21, 2018)
- Module format: CommonJS
- Last CommonJS version: 2.0.0
- TypeScript types: @types/concat-stream
- Node engines: not declared
- Weekly downloads: 38.5M
- License: MIT

## Runtime test results for concat-stream@2.0.0

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

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

ES modules:

```js
import concatStream from "concat-stream";
```

CommonJS:

```js
const concatStream = require("concat-stream");
```

## Module format by version

Derived from the type, main and exports fields of every stable release on npm (37 versions; the newest 37 shown).

| Versions | Format | First published |
|---|---|---|
| 0.0.1 – 2.0.0 | CommonJS | Aug 3, 2012 |

## Frequently asked

**Is concat-stream ESM-only?**

concat-stream@2.0.0 is a CommonJS package. concat-stream ships CommonJS only. require("concat-stream") works on every Node.js version we test (18, 20, 22, 24 and 26) and in Bun. import "concat-stream" 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-stream with ES module syntax?**

Yes. import concatStream from "concat-stream" 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-stream work in Bun?**

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

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

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

## Links

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

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