# Is @csstools/css-parser-algorithms ESM-only? Can you require() it?

> @csstools/css-parser-algorithms@4.0.0 is ESM-only. ESM-only since 4.0.0 — last CommonJS version is 3.0.5.

Algorithms to help you parse CSS from an array of tokens.

Last verified Sep 9, 2026 against @csstools/css-parser-algorithms@4.0.0.

@csstools/css-parser-algorithms dropped its CommonJS build in 4.0.0 (January 2026). The last version with a plain require()-able CommonJS entry is 3.0.5, published May 27, 2025; it declares support for Node.js >=18.

On Node.js 20.19+, 22.12+ and newer, require("@csstools/css-parser-algorithms") works with the latest version: Node.js loads synchronous ES modules through require(). Verified on Node.js 20, 22, 24 and 26. Node.js 18 has no require(esm), and @csstools/css-parser-algorithms@4.0.0 declares Node.js >=20.19.0, so 18 is outside its supported range anyway.

@csstools/css-parser-algorithms@4.0.0 declares engines ">=20.19.0", so Node.js 18 is outside its supported range regardless of module format.

## What to do

1. On Node.js 20.19+, 22.12+ and newer, require("@csstools/css-parser-algorithms") 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 cssParserAlgorithms = await import("@csstools/css-parser-algorithms"). That works on every Node.js version the package supports (>=20.19.0).
3. If you need a synchronous require() or run Node.js 18: npm install @csstools/css-parser-algorithms@3.0.5, the last CommonJS release (published May 27, 2025); it declares Node.js >=18.
4. @csstools/css-parser-algorithms@4.0.0 declares engines ">=20.19.0", so Node.js 18 is unsupported regardless: upgrade Node.js or pin an older release.
5. TypeScript: types are bundled; install nothing extra.

## Facts

- Latest: 4.0.0 (Jan 14, 2026)
- Module format: ESM-only
- Last CommonJS version: 3.0.5
- ESM-only since: 4.0.0 (Jan 14, 2026)
- TypeScript types: bundled
- Node engines: >=20.19.0
- Weekly downloads: 68.0M
- License: MIT

## Runtime test results for @csstools/css-parser-algorithms@4.0.0

Installed and executed on Sep 9, 2026 with require("@csstools/css-parser-algorithms") from a CommonJS file and import "@csstools/css-parser-algorithms" from an ES module.

| Runtime | require("@csstools/css-parser-algorithms") | import "@csstools/css-parser-algorithms" |
|---|---|---|
| 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 @csstools/css-parser-algorithms

ES modules:

```js
import * as cssParserAlgorithms from "@csstools/css-parser-algorithms";
```

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 cssParserAlgorithms = require("@csstools/css-parser-algorithms");

// Any Node.js version the package supports (>=20.19.0), from an async function:
async function main() {
  const cssParserAlgorithms = await import("@csstools/css-parser-algorithms");
}

// Or pin the last CommonJS release (declares Node.js >=18):
// npm install @csstools/css-parser-algorithms@3.0.5
```

## Module format by version

Derived from the type, main and exports fields of every stable release on npm (24 versions; the newest 24 shown).

| Versions | Format | First published |
|---|---|---|
| 4.0.0 | ESM-only | Jan 14, 2026 |
| 1.0.0 – 3.0.5 | Dual (CommonJS + ESM) | Nov 14, 2022 |

## Frequently asked

**Is @csstools/css-parser-algorithms ESM-only?**

@csstools/css-parser-algorithms@4.0.0 is ESM-only. @csstools/css-parser-algorithms dropped its CommonJS build in 4.0.0 (January 2026). The last version with a plain require()-able CommonJS entry is 3.0.5, published May 27, 2025; it declares support for Node.js >=18.

**Which version of @csstools/css-parser-algorithms still supports CommonJS / require()?**

3.0.5 is the last version of @csstools/css-parser-algorithms with a CommonJS build; it declares Node.js >=18. Install it with "npm install @csstools/css-parser-algorithms@3.0.5". Every version from 4.0.0 on is ESM-only.

**How do I use @csstools/css-parser-algorithms from a CommonJS file?**

From a CommonJS file, use a dynamic import inside an async function: const cssParserAlgorithms = await import("@csstools/css-parser-algorithms"). That works on every Node.js version the package supports (>=20.19.0). On Node.js 20.19+, 22.12+ and newer, require("@csstools/css-parser-algorithms") works with the latest version: Node.js loads synchronous ES modules through require(). Verified on Node.js 20, 22, 24 and 26. Alternatively pin @csstools/css-parser-algorithms@3.0.5 (declares Node.js >=18).

**Does @csstools/css-parser-algorithms work in Bun?**

Yes. import "@csstools/css-parser-algorithms" loaded successfully in Bun 1.4.0 on Sep 9, 2026.

**Does @csstools/css-parser-algorithms ship TypeScript types?**

Yes. @csstools/css-parser-algorithms bundles its own type declarations; no @types package is needed.

## Links

- [@csstools/css-parser-algorithms on npm](https://www.npmjs.com/package/@csstools/css-parser-algorithms)
- [Source repository](https://github.com/csstools/postcss-plugins)
- [HTML version](https://canirequire.com/package/@csstools/css-parser-algorithms/)
- [JSON version](https://canirequire.com/package/@csstools/css-parser-algorithms.json)

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