feat: support files other than js to be ESM

CHANGELOG.md

@@ -3,6 +3,7 @@
 ### Features
 
 - `[jest-config]` [**BREAKING**] Default to Node testing environment instead of browser (JSDOM) ([#9874](https://github.com/facebook/jest/pull/9874))
+- `[jest-config, jest-runtime]` Support ESM for files other than `.js` and `.mjs` ([#10823](https://github.com/facebook/jest/pull/10823))
 - `[jest-runner]` [**BREAKING**] set exit code to 1 if test logs after teardown ([#10728](https://github.com/facebook/jest/pull/10728))
 - `[jest-snapshot]`: [**BREAKING**] Make prettier optional for inline snapshots - fall back to string replacement ([#7792](https://github.com/facebook/jest/pull/7792))
 - `[jest-repl, jest-runner]` [**BREAKING**] Run transforms over environment ([#8751](https://github.com/facebook/jest/pull/8751))

docs/Configuration.md

@@ -353,6 +353,23 @@ Default: `false`
 
 Make calling deprecated APIs throw helpful error messages. Useful for easing the upgrade process.
 
+### `extensionsToTreatAsEsm` [array\<string>]
+
+Default: `[]`
+
+Jest will run `.mjs` and `.js` files with nearest `package.json`'s `type` field set to `module` as ECMAScript Modules. If you have any other files that should run with native ESM, you need to specify their file extension here.
+
+> Note: Jest's ESM support is still experimental, see [its docs for more details](ECMAScriptModules.md).
+
+```json
+{
+  ...
+  "jest": {
+    "extensionsToTreatAsEsm": [".ts"]
+  }
+}
+```
+
 ### `extraGlobals` [array\<string>]
 
 Default: `undefined`

docs/ECMAScriptModules.md

@@ -12,8 +12,9 @@ Jest ships with _experimental_ support for ECMAScript Modules (ESM).
 With the warnings out of the way, this is how you activate ESM support in your tests.
 
 1. Ensure you either disable [code transforms](./configuration#transform-objectstring-pathtotransformer--pathtotransformer-object) by passing `transform: {}` or otherwise configure your transformer to emit ESM rather than the default CommonJS (CJS).
-1. Execute `node` with `--experimental-vm-modules`, e.g. `node --experimental-vm-modules node_modules/.bin/jest` or `NODE_OPTIONS=--experimental-vm-modules npx jest` etc.. On Windows, you can use [`cross-env`](https://github.com/kentcdodds/cross-env) to be able to set environment variables
-1. Beyond that, we attempt to follow `node`'s logic for activating "ESM mode" (such as looking at `type` in `package.json` or `mjs` files), see [their docs](https://nodejs.org/api/esm.html#esm_enabling) for details
+1. Execute `node` with `--experimental-vm-modules`, e.g. `node --experimental-vm-modules node_modules/.bin/jest` or `NODE_OPTIONS=--experimental-vm-modules npx jest` etc.. On Windows, you can use [`cross-env`](https://github.com/kentcdodds/cross-env) to be able to set environment variables.
+1. Beyond that, we attempt to follow `node`'s logic for activating "ESM mode" (such as looking at `type` in `package.json` or `mjs` files), see [their docs](https://nodejs.org/api/esm.html#esm_enabling) for details.
+1. If you want to treat other file extensions (such as `ts`) as ESM, please use the [`extensionsToTreatAsEsm` option](Configuration.md#extensionstotreatasesm-arraystring).
 
 ## Differences between ESM and CommonJS
 

e2e/__tests__/__snapshots__/showConfig.test.ts.snap

@@ -15,6 +15,7 @@ exports[`--showConfig outputs config info and exits 1`] = `
       "detectLeaks": false,
       "detectOpenHandles": false,
       "errorOnDeprecated": false,
+      "extensionsToTreatAsEsm": [],
       "extraGlobals": [],
       "forceCoverageMatch": [],
       "globals": {},

e2e/__tests__/nativeEsmTypescript.test.ts

@@ -0,0 +1,26 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+import {resolve} from 'path';
+import {onNodeVersions} from '@jest/test-utils';
+import {json as runJest} from '../runJest';
+
+const DIR = resolve(__dirname, '../native-esm-typescript');
+
+// The versions where vm.Module exists and commonjs with "exports" is not broken
+onNodeVersions('^12.16.0 || >=13.7.0', () => {
+  test('runs TS test with native ESM', () => {
+    const {exitCode, json} = runJest(DIR, [], {
+      nodeOptions: '--experimental-vm-modules',
+    });
+
+    expect(exitCode).toBe(0);
+
+    expect(json.numTotalTests).toBe(2);
+    expect(json.numPassedTests).toBe(2);
+  });
+});

e2e/native-esm-typescript/__tests__/double.test.ts

@@ -0,0 +1,16 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+import {double} from '../double';
+
+test('test double', () => {
+  expect(double(2)).toBe(4);
+});
+
+test('test import.meta', () => {
+  expect(typeof import.meta.url).toBe('string');
+});

e2e/native-esm-typescript/babel.config.js

@@ -0,0 +1,11 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+module.exports = {
+  // importantly this does _not_ include `preset-env`
+  presets: ['@babel/preset-typescript'],
+};

e2e/native-esm-typescript/double.ts

@@ -0,0 +1,10 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+export function double(num: number): number {
+  return num * 2;
+}

e2e/native-esm-typescript/package.json

@@ -0,0 +1,8 @@
+{
+  "name": "native-esm-typescript",
+  "version": "1.0.0",
+  "jest": {
+    "extensionsToTreatAsEsm": [".ts"],
+    "testEnvironment": "node"
+  }
+}

packages/jest-circus/src/legacy-code-todo-rewrite/jestAdapter.ts

@@ -72,18 +72,21 @@ const jestAdapter = async (
   });
 
   for (const path of config.setupFilesAfterEnv) {
-    // TODO: remove ? in Jest 26
-    const esm = runtime.unstable_shouldLoadAsEsm?.(path);
+    const esm = runtime.unstable_shouldLoadAsEsm(
+      path,
+      config.extensionsToTreatAsEsm,
+    );
 
     if (esm) {
       await runtime.unstable_importModule(path);
     } else {
       runtime.requireModule(path);
     }
   }
-
-  // TODO: remove ? in Jest 26
-  const esm = runtime.unstable_shouldLoadAsEsm?.(testPath);
+  const esm = runtime.unstable_shouldLoadAsEsm(
+    testPath,
+    config.extensionsToTreatAsEsm,
+  );
 
   if (esm) {
     await runtime.unstable_importModule(testPath);

packages/jest-config/package.json

@@ -46,6 +46,8 @@
     "@types/glob": "^7.1.1",
     "@types/graceful-fs": "^4.1.3",
     "@types/micromatch": "^4.0.0",
+    "jest-snapshot-serializer-raw": "^1.1.0",
+    "strip-ansi": "^6.0.0",
     "ts-node": "^9.0.0",
     "typescript": "^4.0.3"
   },

packages/jest-config/src/Defaults.ts

@@ -26,6 +26,7 @@ const defaultOptions: Config.DefaultOptions = {
   coverageReporters: ['json', 'text', 'lcov', 'clover'],
   errorOnDeprecated: false,
   expand: false,
+  extensionsToTreatAsEsm: [],
   forceCoverageMatch: [],
   globals: {},
   haste: {

packages/jest-config/src/ValidConfig.ts

@@ -44,6 +44,7 @@ const initialOptions: Config.InitialOptions = {
   } as const),
   errorOnDeprecated: false,
   expand: false,
+  extensionsToTreatAsEsm: [],
   extraGlobals: [],
   filter: '<rootDir>/filter.js',
   forceCoverageMatch: ['**/*.t.js'],

packages/jest-config/src/__tests__/__snapshots__/normalize.test.js.snap

@@ -91,6 +91,43 @@ exports[`displayName should throw an error when displayName is using invalid val
 <red></>"
 `;
 
+exports[`extensionsToTreatAsEsm should enforce leading dots 1`] = `
+● Validation Error:
+
+  Option: extensionsToTreatAsEsm: ['ts'] includes a string that does not start with a period (.).
+  Please change your configuration to extensionsToTreatAsEsm: ['.ts'].
+
+  Configuration Documentation:
+  https://jestjs.io/docs/configuration.html
+`;
+
+exports[`extensionsToTreatAsEsm throws on .cjs 1`] = `
+● Validation Error:
+
+  Option: extensionsToTreatAsEsm: ['.cjs'] includes '.cjs' which is always treated as CommonJS.
+
+  Configuration Documentation:
+  https://jestjs.io/docs/configuration.html
+`;
+
+exports[`extensionsToTreatAsEsm throws on .js 1`] = `
+● Validation Error:
+
+  Option: extensionsToTreatAsEsm: ['.js'] includes '.js' which is always inferred based on type in its nearest package.json.
+
+  Configuration Documentation:
+  https://jestjs.io/docs/configuration.html
+`;
+
+exports[`extensionsToTreatAsEsm throws on .mjs 1`] = `
+● Validation Error:
+
+  Option: extensionsToTreatAsEsm: ['.mjs'] includes '.mjs' which is always treated as an ECMAScript Module.
+
+  Configuration Documentation:
+  https://jestjs.io/docs/configuration.html
+`;
+
 exports[`preset throws when module was found but no "jest-preset.js" or "jest-preset.json" files 1`] = `
 "<red><bold><bold>● </><bold>Validation Error</>:</>
 <red></>

packages/jest-config/src/__tests__/normalize.test.js

@@ -8,6 +8,8 @@
 
 import crypto from 'crypto';
 import path from 'path';
+import {wrap} from 'jest-snapshot-serializer-raw';
+import stripAnsi from 'strip-ansi';
 import {escapeStrForRegex} from 'jest-regex-util';
 import Defaults from '../Defaults';
 import {DEFAULT_JS_PATTERN} from '../constants';
@@ -1713,3 +1715,36 @@ describe('testTimeout', () => {
     ).toThrowErrorMatchingSnapshot();
   });
 });
+
+describe('extensionsToTreatAsEsm', () => {
+  function matchErrorSnapshot(callback) {
+    expect.assertions(1);
+
+    try {
+      callback();
+    } catch (error) {
+      expect(wrap(stripAnsi(error.message).trim())).toMatchSnapshot();
+    }
+  }
+
+  it('should pass valid config through', () => {
+    const {options} = normalize(
+      {extensionsToTreatAsEsm: ['.ts'], rootDir: '/root/'},
+      {},
+    );
+
+    expect(options.extensionsToTreatAsEsm).toEqual(['.ts']);
+  });
+
+  it('should enforce leading dots', () => {
+    matchErrorSnapshot(() =>
+      normalize({extensionsToTreatAsEsm: ['ts'], rootDir: '/root/'}, {}),
+    );
+  });
+
+  it.each(['.js', '.mjs', '.cjs'])('throws on %s', ext => {
+    matchErrorSnapshot(() =>
+      normalize({extensionsToTreatAsEsm: [ext], rootDir: '/root/'}, {}),
+    );
+  });
+});

packages/jest-config/src/index.ts

@@ -178,6 +178,7 @@ const groupOptions = (
     detectOpenHandles: options.detectOpenHandles,
     displayName: options.displayName,
     errorOnDeprecated: options.errorOnDeprecated,
+    extensionsToTreatAsEsm: options.extensionsToTreatAsEsm,
     extraGlobals: options.extraGlobals,
     filter: options.filter,
     forceCoverageMatch: options.forceCoverageMatch,

packages/jest-config/src/normalize.ts

@@ -482,6 +482,63 @@ const showTestPathPatternError = (testPathPattern: string) => {
   );
 };
 
+function validateExtensionsToTreatAsEsm(
+  extensionsToTreatAsEsm: Config.InitialOptions['extensionsToTreatAsEsm'],
+) {
+  if (!extensionsToTreatAsEsm || extensionsToTreatAsEsm.length === 0) {
+    return;
+  }
+
+  function printConfig(opts: Array<string>) {
+    const string = opts.map(ext => `'${ext}'`).join(', ');
+
+    return `${chalk.bold(`extensionsToTreatAsEsm: [${string}]`)}`;
+  }
+
+  const extensionWithoutDot = extensionsToTreatAsEsm.some(
+    ext => !ext.startsWith('.'),
+  );
+
+  if (extensionWithoutDot) {
+    throw createConfigError(
+      `  Option: ${printConfig(
+        extensionsToTreatAsEsm,
+      )} includes a string that does not start with a period (${chalk.bold(
+        '.',
+      )}).
+  Please change your configuration to ${printConfig(
+    extensionsToTreatAsEsm.map(ext => (ext.startsWith('.') ? ext : `.${ext}`)),
+  )}.`,
+    );
+  }
+
+  if (extensionsToTreatAsEsm.includes('.js')) {
+    throw createConfigError(
+      `  Option: ${printConfig(extensionsToTreatAsEsm)} includes ${chalk.bold(
+        "'.js'",
+      )} which is always inferred based on ${chalk.bold(
+        'type',
+      )} in its nearest ${chalk.bold('package.json')}.`,
+    );
+  }
+
+  if (extensionsToTreatAsEsm.includes('.cjs')) {
+    throw createConfigError(
+      `  Option: ${printConfig(extensionsToTreatAsEsm)} includes ${chalk.bold(
+        "'.cjs'",
+      )} which is always treated as CommonJS.`,
+    );
+  }
+
+  if (extensionsToTreatAsEsm.includes('.mjs')) {
+    throw createConfigError(
+      `  Option: ${printConfig(extensionsToTreatAsEsm)} includes ${chalk.bold(
+        "'.mjs'",
+      )} which is always treated as an ECMAScript Module.`,
+    );
+  }
+}
+
 export default function normalize(
   initialOptions: Config.InitialOptions,
   argv: Config.Argv,
@@ -577,6 +634,8 @@ export default function normalize(
     });
   }
 
+  validateExtensionsToTreatAsEsm(options.extensionsToTreatAsEsm);
+
   const optionKeys = Object.keys(options) as Array<keyof Config.InitialOptions>;
 
   optionKeys.reduce((newOptions, key: keyof Config.InitialOptions) => {
@@ -881,6 +940,7 @@ export default function normalize(
       case 'detectOpenHandles':
       case 'errorOnDeprecated':
       case 'expand':
+      case 'extensionsToTreatAsEsm':
       case 'extraGlobals':
       case 'globals':
       case 'findRelatedTests':

packages/jest-core/src/lib/__tests__/__snapshots__/logDebugMessages.test.ts.snap

@@ -12,6 +12,7 @@ exports[`prints the config object 1`] = `
     "detectLeaks": false,
     "detectOpenHandles": false,
     "errorOnDeprecated": false,
+    "extensionsToTreatAsEsm": [],
     "extraGlobals": [],
     "forceCoverageMatch": [],
     "globals": {},

packages/jest-jasmine2/src/index.ts

@@ -149,8 +149,10 @@ async function jasmine2(
     });
 
   for (const path of config.setupFilesAfterEnv) {
-    // TODO: remove ? in Jest 26
-    const esm = runtime.unstable_shouldLoadAsEsm?.(path);
+    const esm = runtime.unstable_shouldLoadAsEsm(
+      path,
+      config.extensionsToTreatAsEsm,
+    );
 
     if (esm) {
       await runtime.unstable_importModule(path);
@@ -163,9 +165,10 @@ async function jasmine2(
     const testNameRegex = new RegExp(globalConfig.testNamePattern, 'i');
     env.specFilter = (spec: Spec) => testNameRegex.test(spec.getFullName());
   }
-
-  // TODO: remove ? in Jest 26
-  const esm = runtime.unstable_shouldLoadAsEsm?.(testPath);
+  const esm = runtime.unstable_shouldLoadAsEsm(
+    testPath,
+    config.extensionsToTreatAsEsm,
+  );
 
   if (esm) {
     await runtime.unstable_importModule(testPath);