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

> bser@2.1.1 is a CommonJS package. CommonJS — require() works on every Node.js version we test.

JavaScript implementation of the BSER Binary Serialization

Last verified Sep 9, 2026 against bser@2.1.1.

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

## Facts

- Latest: 2.1.1 (Oct 22, 2019)
- Module format: CommonJS
- Last CommonJS version: 2.1.1
- TypeScript types: @types/bser
- Node engines: not declared
- Weekly downloads: 34.0M
- License: Apache-2.0

## Runtime test results for bser@2.1.1

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

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

ES modules:

```js
import bser from "bser";
```

CommonJS:

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

## Module format by version

Derived from the type, main and exports fields of every stable release on npm (7 versions; the newest 7 shown).

| Versions | Format | First published |
|---|---|---|
| 1.0.0 – 2.1.1 | CommonJS | Aug 24, 2015 |

## Frequently asked

**Is bser ESM-only?**

bser@2.1.1 is a CommonJS package. bser ships CommonJS only. require("bser") works on every Node.js version we test (18, 20, 22, 24 and 26) and in Bun. import "bser" 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 bser with ES module syntax?**

Yes. import bser from "bser" 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 bser work in Bun?**

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

**Does bser ship TypeScript types?**

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

## Links

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

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