v11 breaks ESM compatibility

[david-guevara-gorillalogic]

Here is a repo with the reproduction: https://github.com/david-guevara-gorillalogic/mailosaur-esm-issue.

Reproduction steps

1. Clone https://github.com/david-guevara-gorillalogic/mailosaur-esm-issue
2. Execute pnpm install
3. Execute pnpm run check (i.e. tsc --noEmit)
4. See the type error.

Expected result

TypeScript should compile without errors.

Current result

TS2351: This expression is not constructable.
Type 'typeof import(".../node_modules/mailosaur/cjs/mailosaur")' has no construct signatures.

Details

The code is essentially:

import MailosaurClient from "mailosaur";
const client = new MailosaurClient("not-a-real-api-key");

With this tsconfig:

{
  "compilerOptions": {
    "module": "NodeNext"
  }
}

[jm-mailosaur]

@david-guevara-gorillalogic thanks for raising this - our team are looking at this now.

[jm-mailosaur]

Released now as 11.0.2

[romansp]

@jm-mailosaur Thanks for quick fix but I'm afraid this needs to be reopened. Just updated to 11.0.2 but something is still off here. Seems like operation files are missing the same ESM/CommonJS compatibility as main entry file. Or maybe it's not needed at all if there's a separate esm build?

#85 seemed to fix tsc compilation but we're now seeing issues in runtime.

We use mailosaur in e2e tests with playwright and vite so our actual tsconfig is "module": "esnext" and "moduleResolution": "bundler". But it doesn't work with "module": "NodeNext" either.

➜  mailosaur-esm-issue git:(main) ✗ pnpm run check-and-run

> check-and-run
> tsc && node ./dist/index.js

file:///Users/roman/Documents/dev/mailosaur-esm-issue/node_modules/.pnpm/mailosaur@11.0.2_@types+node@24.10.13/node_modules/mailosaur/esm/operations/analysis.js:52
module.exports = Analysis;
^

ReferenceError: module is not defined in ES module scope
This file is being treated as an ES module because it has a '.js' file extension and '/Users/roman/Documents/dev/mailosaur-esm-issue/package.json' contains "type": "module". To treat it as a CommonJS script, rename it to use the '.cjs' file extension.
    at file:///Users/roman/Documents/dev/mailosaur-esm-issue/node_modules/.pnpm/mailosaur@11.0.2_@types+node@24.10.13/node_modules/mailosaur/esm/operations/analysis.js:52:1
    at ModuleJob.run (node:internal/modules/esm/module_job:413:25)
    at async onImport.tracePromise.__proto__ (node:internal/modules/esm/loader:660:26)
    at async asyncRunEntryPointWithESMLoader (node:internal/modules/run_main:101:5)

Node.js v24.13.0

minimal repro: https://github.com/romansp/mailosaur-esm-issue

1. Clone
2. Execute pnpm install
3. Execute pnpm run check-and-run. this will compile via tsc and run with node

Node.js version: v24.13.0