How to use moduleTypes with a node_modules outside of the tsconfig's package

[DrJKL]

I'm trying to get a project working with a mix of CommonJS (that I can't migrate to ESM) and ESM dependencies, in this case d3-format.

I've gotten the require to point to the dist folder using

"paths": {
  "d3-format": ["../node_modules/d3-format/dist/d3-format.min.js"]
}

I do have "require": ["tsconfig-paths/register"],

But this gives me d3-format.min.js is treated as an ES module file as it is a .js file whose nearest parent package.json contains "type": "module" which declares all .js files in that package scope as ES modules.

I've tried a few different "moduleTypes" but none of them seem to apply to the require()

"moduleTypes": {
  "../node_modules/**/*": "cjs",
  "**/*": "cjs",
  "*": "cjs",
  // ...
},

Any help would be appreciated. We're also using "swc": true if that matters.

Related: #2077 (comment)

[agammann]

A moduleTypes glob only affects files that ts-node transforms; it isn't a general override for Node's package loader. .js files need allowJs to be transformed, and node_modules is ignored by default. Remapping a dependency's UMD .js file doesn't change that package's "type": "module" boundary.

You can keep your entry point CommonJS and load the ESM dependency through a native dynamic import. Here is a TypeScript-compiler recipe that does not use SWC:

{
  "compilerOptions": {
    "target": "ES2021",
    "module": "NodeNext",
    "moduleResolution": "NodeNext",
    "strict": true
  },
  "ts-node": {
    "swc": false
  }
}

Save this as main.cts (.cts makes the entry CommonJS):

async function main() {
  const { format } = await import('d3-format');
  console.log(format(',.2f')(1234.5));
}

void main();

Run npx ts-node main.cts. Remove the d3-format paths remap and the broad moduleTypes overrides for this recipe, so the import resolves the package's normal ESM export.

I tested ts-node 10.9.2, TypeScript 5.9.3 and d3-format 3.1.0 on Node 24.19.0: it printed 1,234.50, and the emitted CommonJS retained native import() rather than turning it into require(). This avoids converting the ESM dependency or moving your whole application to ESM. It does not test the SWC branch from your original configuration. Module overrides, ignored files.