Type stripping with VM modules

[slagiewka]

Version

v23.6.0

Platform

Darwin mbp.local 23.6.0 Darwin Kernel Version 23.6.0: Mon Jul 29 21:14:30 PDT 2024; root:xnu-10063.141.2~1/RELEASE_ARM64_T6000 arm64

Subsystem

No response

What steps will reproduce the bug?

1. Get jest
2. Configure jest to run ESM

export default {
  transform: {},
  extensionsToTreatAsEsm: ['.ts'],
}

3. Write a simple type annotation inside example.test.ts.
4. Run node --experimental-vm-modules node_modules/jest/bin/jest.js

Reproduction repository: https://github.com/slagiewka/jest_node_ts

How often does it reproduce? Is there a required condition?

Always.

What is the expected behavior? Why is that the expected behavior?

Type stripping works with Jest and ESM (via VM modules).

What do you see instead?

❯ node --experimental-vm-modules node_modules/jest/bin/jest.js
 FAIL  ./example.test.ts
  ● Test suite failed to run

    SyntaxError: Unexpected token ':'

      at Runtime.loadEsmModule (node_modules/jest-runtime/build/index.js:516:20

The corresponding line in source code: https://github.com/jestjs/jest/blob/611d1a4ba0008d67b5dcda485177f0813b2b573e/packages/jest-runtime/src/index.ts#L501

Additional information

I'm not sure if this is something that is an issue on node or Jest side. I'll be happy to report it to Jest if there's nothing that node can do here.

[slagiewka]

Looking at the source of issue, this is the minimal reproduction without importing anything external:

import { SourceTextModule } from "node:vm";

new SourceTextModule(`let foobar: string;`);

[joyeecheung]

SourceTextModule corresponds to a SourceTextModule in the ECMAScript specification, so it's JavaScript. To strip the types, use module.stripTypeScriptTypes() to process the code first before passing it into SourceTextModule.