🚀 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.