[Native ESM] [ts-jest@next] ReferenceError: exports is not defined

[qnighy]

🐛 Bug Report

Under a certain condition with native ESM support, the test fails with ReferenceError: exports is not defined.

To Reproduce

package.json:

{
  "private": true,
  "type": "module",
  "devDependencies": {
    "@babel/core": "^7.13.1",
    "jest": "^27.0.0-next.3",
    "ts-jest": "^27.0.0-next.6",
    "typescript": "^4.1.5"
  },
  "scripts": {
    "test": "node --experimental-vm-modules node_modules/.bin/jest --no-cache"
  },
  "jest": {
    "transform": {
      "\\.[jt]sx?$": "ts-jest"
    },
    "extensionsToTreatAsEsm": [
      ".ts"
    ]
  }
}

lib.ts:

export const X = 42;

lib.test.ts:

import { X } from "./lib";

test("X", () => {
  expect(X).toBe(42);
});

tsconfig.json:

{
  "compilerOptions": {
    "target": "ESNext",
    "module": "ESNext",
    "lib": ["ES2015", "DOM"],
    "allowJs": true,
    "checkJs": true,
    "isolatedModules": true,
    "strict": true,
    "moduleResolution": "node",
    "esModuleInterop": true,
  }
}

$ node --version
v14.15.5
$ yarn test
yarn run v1.22.5
$ node --experimental-vm-modules node_modules/.bin/jest --no-cache
(node:23494) ExperimentalWarning: VM Modules is an experimental feature. This feature could change at any time
(Use `node --trace-warnings ...` to show where the warning was created)
 FAIL  ./lib.test.ts
  ● Test suite failed to run

    ReferenceError: exports is not defined

      1 | import { X } from "./lib";
    > 2 |
        | ^
      3 | test("X", () => {
      4 |   expect(X).toBe(42);
      5 | });

      at lib.test.ts:2:23

Test Suites: 1 failed, 1 total
Tests:       0 total
Snapshots:   0 total
Time:        2.343 s
Ran all test suites.
error Command failed with exit code 1.
info Visit https://yarnpkg.com/en/docs/cli/run for documentation about this command.

And without --no-cache, the following behaviors are observed:

• Change lib.ts a bit (e.g. adding / removing empty lines) and rerun the test: the test starts to fail.
• Change lib.test.ts a bit (e.g. adding / removing empty lines) and rerun the test: the test starts to pass.

Expected behavior

The test is expected to always pass.

Link to repo (highly encouraged)

https://github.com/qnighy/ts-jest-esm-failure-example

The example above was extracted from https://github.com/qnighy/ts-type-module-example.

Debug log:

https://gist.github.com/qnighy/9ba2c6b2023c4a8dad38c53faf4ed592

envinfo

System:
    OS: Ubuntu 20.04 on WSL2
    Node version: v14.15.5

Npm packages:
    jest: 27.0.0-next.3
    ts-jest: 27.0.0-next.6
    typescript: 4.1.5
    babel(optional): 7.13.1

[ahnpnl]

Hi, would you please check with Jest repo. IIRC export is not supported yet. We only transpile ts to js and Jest runs the transpires codes so I don’t think this is ts-jest issue.

[ahnpnl]

See more at jestjs/jest#9430

[qnighy]

See more at jestjs/jest#9430

@ahnpnl Yes, I was experimenting with the native ESM support mentioned in jestjs/jest#9430, and by your comment there I thought it's being implemented in ts-jest@next. Is my understanding wrong, or shouldn't have I filed ts-jest@next's issue here?

[qnighy]

A similar configuration works with babel-jest@next so I thought it's ts-jest@next's issue

[ahnpnl]

I see you missed one important thing, enable support esm config option for ts-jest. If you go to online doc and choose next version, you will find the guide :)

[qnighy]

Aaah, this one! https://kulshekhar.github.io/ts-jest/docs/next/guides/esm-support

Thanks! It turned out to be my mistake.