## Problem `esm@3.2.25` (last release: 2019) is no longer compatible with Node 20+. Running `npm test` fails immediately:

SyntaxError: Cannot use import statement outside a module

This means contributors on modern Node versions cannot run the test suite locally.

## Root cause

The test command uses `-r esm` which hooks into Node's CJS module loader to support ESM syntax in test files. This mechanism stopped working in Node 20+ due to changes in how Node handles module loading hooks.

## Reproduction

```bash node --version # v20.x or higher npm test # fails ```

What still works

The library itself (dist/clsx.js, dist/clsx.mjs) works fine for consumers on Node 20+. Only the test suite is affected.

The constraint

Since the package declares "engines": ">=6" and CI covers Node 8–18, a simple solution of removing -r esm is not straightforward — it works on Node 20+ but breaks on Node 8–18 (no native ESM for .js files without "type": "module").

Possible approaches

1. Rename test/*.js → test/*.mjs (explicit ESM marker) — worth investigating for old Node compat 2. Add "type": "module" to package.json + rename dist/clsx.js → .cjs + update exports — larger change, affects build output 3. Replace esm with a maintained modern alternative — adds a dev dependency 4. Two CI workflows (legacy Node 8–18 + modern Node 20+) — parallel coverage without dropping either

Question

What's the preferred direction? Happy to open a PR once the approach is clear.