[Feature]: support node's type stripping

[slagiewka]

🚀 Feature Proposal

Since node is going into the direction of (partial) TypeScript support it might be beneficial for Jest to support that flow automatically together with #9430.

The support can be done on a best-effort basis.

Motivation

Less configuration required
Less dependencies in use - no need to run through Babel
Faster execution ¹
Quicker way from bootstrap to running suites

Example

Consider the native-esm-typescript E2E test.

Should the config be changed to:

{
  "name": "native-esm-typescript",
  "version": "1.0.0",
  "jest": {
   "transform": {}, // effectively disables `babel-jest`
    "extensionsToTreatAsEsm": [
      ".ts"
    ],
    "testEnvironment": "node"
  }
}

However, even with node 22 and 23 where type stripping (or transformation) can be enabled, this will fail inside jest-runtime where the vm.SourceTextModule expects plain JS and fails inevitably on first : type it finds.

Node v22.13.0 and v23.2.0 have a module helper stripTypeScriptTypes.

It is possible to write a small shim transformer - my PoC:
jest.typestripping.mjs

import { stripTypeScriptTypes } from 'node:module';

export default {
  process(sourceText) {
    return {code: stripTypeScriptTypes(sourceText)};
  }
};

jest.typetransforming.mjs

import { stripTypeScriptTypes } from 'node:module';

export default {
  process(sourceText) {
    return {code: stripTypeScriptTypes(sourceText, {mode: 'transform'})};
  }
};

And configure jest to run it:

{
  "name": "native-esm-typescript",
  "version": "1.0.0",
  "jest": {
    "transform": {
      "\\.[jt]sx?$": "<rootDir>/jest.typestripping.mjs", // if no transforms are necessary
      "\\.[jt]sx?$": "<rootDir>/jest.typetransforming.mjs", // if using enums or other unsupported syntax
     },
    "extensionsToTreatAsEsm": [
        ".ts"
    ],
    "testEnvironment": "node"
  }
}

Using this with my integration tests works wonders. It replaces ts-jest and speeds the execution time from ~30s to ~7-8s.

The output string can also be equipped with a source map (for transform cases) and source URL to annotate in the source map.

Pitch

The feature can be hooked into jest-runtime and run automatically depending on available APIs. The runtime already does various checks against node:module, e.g. for createRequire.

Running ESM (which requires disabling transforms) with TypeScript could therefore be as effortless as possible for those wanting to join and use as less build steps as possible.

Footnotes

1. depending on which transpiler is used and in which mode ↩

[github-actions]

This issue is stale because it has been open 30 days with no activity. Remove stale label or comment or this will be closed in 30 days.

[slagiewka]

Is this issue tracker dead?

[github-actions]

This issue is stale because it has been open 30 days with no activity. Remove stale label or comment or this will be closed in 30 days.

[metaskills]

Does this work? I could not get 23.10.0 to work using your work arounds.

[github-actions]

This issue is stale because it has been open 30 days with no activity. Remove stale label or comment or this will be closed in 30 days.