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feat: support files other than js to be ESM
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‎CHANGELOG.md

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@@ -4,6 +4,7 @@
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- `[jest-config]` [**BREAKING**] Default to Node testing environment instead of browser (JSDOM) ([#9874](https://github.com/facebook/jest/pull/9874))
66
- `[jest-config]` [**BREAKING**] Use `jest-circus` as default test runner ([#10686](https://github.com/facebook/jest/pull/10686))
7+
- `[jest-config, jest-runtime]` Support ESM for files other than `.js` and `.mjs` ([#10823](https://github.com/facebook/jest/pull/10823))
78
- `[jest-runner]` [**BREAKING**] set exit code to 1 if test logs after teardown ([#10728](https://github.com/facebook/jest/pull/10728))
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- `[jest-snapshot]`: [**BREAKING**] Make prettier optional for inline snapshots - fall back to string replacement ([#7792](https://github.com/facebook/jest/pull/7792))
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- `[jest-repl, jest-runner]` [**BREAKING**] Run transforms over environment ([#8751](https://github.com/facebook/jest/pull/8751))

‎docs/Configuration.md

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@@ -353,6 +353,23 @@ Default: `false`
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Make calling deprecated APIs throw helpful error messages. Useful for easing the upgrade process.
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### `extensionsToTreatAsEsm` [array\<string>]
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Default: `[]`
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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.
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> Note: Jest's ESM support is still experimental, see [its docs for more details](ECMAScriptModules.md).
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```json
365+
{
366+
...
367+
"jest": {
368+
"extensionsToTreatAsEsm": [".ts"]
369+
}
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}
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```
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### `extraGlobals` [array\<string>]
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Default: `undefined`

‎docs/ECMAScriptModules.md

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@@ -12,8 +12,9 @@ Jest ships with _experimental_ support for ECMAScript Modules (ESM).
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With the warnings out of the way, this is how you activate ESM support in your tests.
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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).
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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
16-
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
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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.
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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.
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1. If you want to treat other file extensions (such as `ts`) as ESM, please use the [`extensionsToTreatAsEsm` option](Configuration.md#extensionstotreatasesm-arraystring).
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## Differences between ESM and CommonJS
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‎e2e/__tests__/__snapshots__/showConfig.test.ts.snap

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

‎e2e/__tests__/nativeEsmTypescript.test.ts

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@@ -0,0 +1,26 @@
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/**
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* Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.
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*
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* This source code is licensed under the MIT license found in the
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* LICENSE file in the root directory of this source tree.
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*/
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import {resolve} from 'path';
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import {onNodeVersions} from '@jest/test-utils';
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import {json as runJest} from '../runJest';
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const DIR = resolve(__dirname, '../native-esm-typescript');
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// The versions where vm.Module exists and commonjs with "exports" is not broken
15+
onNodeVersions('^12.16.0 || >=13.7.0', () => {
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test('runs TS test with native ESM', () => {
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const {exitCode, json} = runJest(DIR, [], {
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nodeOptions: '--experimental-vm-modules',
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});
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expect(exitCode).toBe(0);
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expect(json.numTotalTests).toBe(2);
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expect(json.numPassedTests).toBe(2);
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});
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});

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

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/**
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* Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.
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*
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* This source code is licensed under the MIT license found in the
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* LICENSE file in the root directory of this source tree.
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*/
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import {double} from '../double';
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test('test double', () => {
11+
expect(double(2)).toBe(4);
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});
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test('test import.meta', () => {
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expect(typeof import.meta.url).toBe('string');
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});

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

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

‎e2e/native-esm-typescript/double.ts

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

‎e2e/native-esm-typescript/package.json

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

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

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@@ -72,18 +72,21 @@ const jestAdapter = async (
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});
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for (const path of config.setupFilesAfterEnv) {
75-
// TODO: remove ? in Jest 26
76-
const esm = runtime.unstable_shouldLoadAsEsm?.(path);
75+
const esm = runtime.unstable_shouldLoadAsEsm(
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path,
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config.extensionsToTreatAsEsm,
78+
);
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7880
if (esm) {
7981
await runtime.unstable_importModule(path);
8082
} else {
8183
runtime.requireModule(path);
8284
}
8385
}
84-
85-
// TODO: remove ? in Jest 26
86-
const esm = runtime.unstable_shouldLoadAsEsm?.(testPath);
86+
const esm = runtime.unstable_shouldLoadAsEsm(
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testPath,
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config.extensionsToTreatAsEsm,
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);
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if (esm) {
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await runtime.unstable_importModule(testPath);

‎packages/jest-config/package.json

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

‎packages/jest-config/src/Defaults.ts

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

‎packages/jest-config/src/ValidConfig.ts

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} as const),
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errorOnDeprecated: false,
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expand: false,
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extensionsToTreatAsEsm: [],
4748
extraGlobals: [],
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filter: '<rootDir>/filter.js',
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forceCoverageMatch: ['**/*.t.js'],

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

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<red></>"
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`;
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exports[`extensionsToTreatAsEsm should enforce leading dots 1`] = `
95+
● Validation Error:
96+
97+
Option: extensionsToTreatAsEsm: ['ts'] includes a string that does not start with a period (.).
98+
Please change your configuration to extensionsToTreatAsEsm: ['.ts'].
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100+
Configuration Documentation:
101+
https://jestjs.io/docs/configuration.html
102+
`;
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104+
exports[`extensionsToTreatAsEsm throws on .cjs 1`] = `
105+
● Validation Error:
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107+
Option: extensionsToTreatAsEsm: ['.cjs'] includes '.cjs' which is always treated as CommonJS.
108+
109+
Configuration Documentation:
110+
https://jestjs.io/docs/configuration.html
111+
`;
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113+
exports[`extensionsToTreatAsEsm throws on .js 1`] = `
114+
● Validation Error:
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116+
Option: extensionsToTreatAsEsm: ['.js'] includes '.js' which is always inferred based on type in its nearest package.json.
117+
118+
Configuration Documentation:
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https://jestjs.io/docs/configuration.html
120+
`;
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122+
exports[`extensionsToTreatAsEsm throws on .mjs 1`] = `
123+
● Validation Error:
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125+
Option: extensionsToTreatAsEsm: ['.mjs'] includes '.mjs' which is always treated as an ECMAScript Module.
126+
127+
Configuration Documentation:
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https://jestjs.io/docs/configuration.html
129+
`;
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94131
exports[`preset throws when module was found but no "jest-preset.js" or "jest-preset.json" files 1`] = `
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"<red><bold><bold>● </><bold>Validation Error</>:</>
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<red></>

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

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import crypto from 'crypto';
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import path from 'path';
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import {wrap} from 'jest-snapshot-serializer-raw';
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import stripAnsi from 'strip-ansi';
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import {escapeStrForRegex} from 'jest-regex-util';
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import Defaults from '../Defaults';
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import {DEFAULT_JS_PATTERN} from '../constants';
@@ -1728,3 +1730,36 @@ describe('testTimeout', () => {
17281730
).toThrowErrorMatchingSnapshot();
17291731
});
17301732
});
1733+
1734+
describe('extensionsToTreatAsEsm', () => {
1735+
function matchErrorSnapshot(callback) {
1736+
expect.assertions(1);
1737+
1738+
try {
1739+
callback();
1740+
} catch (error) {
1741+
expect(wrap(stripAnsi(error.message).trim())).toMatchSnapshot();
1742+
}
1743+
}
1744+
1745+
it('should pass valid config through', () => {
1746+
const {options} = normalize(
1747+
{extensionsToTreatAsEsm: ['.ts'], rootDir: '/root/'},
1748+
{},
1749+
);
1750+
1751+
expect(options.extensionsToTreatAsEsm).toEqual(['.ts']);
1752+
});
1753+
1754+
it('should enforce leading dots', () => {
1755+
matchErrorSnapshot(() =>
1756+
normalize({extensionsToTreatAsEsm: ['ts'], rootDir: '/root/'}, {}),
1757+
);
1758+
});
1759+
1760+
it.each(['.js', '.mjs', '.cjs'])('throws on %s', ext => {
1761+
matchErrorSnapshot(() =>
1762+
normalize({extensionsToTreatAsEsm: [ext], rootDir: '/root/'}, {}),
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);
1764+
});
1765+
});

‎packages/jest-config/src/index.ts

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detectOpenHandles: options.detectOpenHandles,
179179
displayName: options.displayName,
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errorOnDeprecated: options.errorOnDeprecated,
181+
extensionsToTreatAsEsm: options.extensionsToTreatAsEsm,
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extraGlobals: options.extraGlobals,
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filter: options.filter,
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forceCoverageMatch: options.forceCoverageMatch,

‎packages/jest-config/src/normalize.ts

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@@ -482,6 +482,63 @@ const showTestPathPatternError = (testPathPattern: string) => {
482482
);
483483
};
484484

485+
function validateExtensionsToTreatAsEsm(
486+
extensionsToTreatAsEsm: Config.InitialOptions['extensionsToTreatAsEsm'],
487+
) {
488+
if (!extensionsToTreatAsEsm || extensionsToTreatAsEsm.length === 0) {
489+
return;
490+
}
491+
492+
function printConfig(opts: Array<string>) {
493+
const string = opts.map(ext => `'${ext}'`).join(', ');
494+
495+
return chalk.bold(`extensionsToTreatAsEsm: [${string}]`);
496+
}
497+
498+
const extensionWithoutDot = extensionsToTreatAsEsm.some(
499+
ext => !ext.startsWith('.'),
500+
);
501+
502+
if (extensionWithoutDot) {
503+
throw createConfigError(
504+
` Option: ${printConfig(
505+
extensionsToTreatAsEsm,
506+
)} includes a string that does not start with a period (${chalk.bold(
507+
'.',
508+
)}).
509+
Please change your configuration to ${printConfig(
510+
extensionsToTreatAsEsm.map(ext => (ext.startsWith('.') ? ext : `.${ext}`)),
511+
)}.`,
512+
);
513+
}
514+
515+
if (extensionsToTreatAsEsm.includes('.js')) {
516+
throw createConfigError(
517+
` Option: ${printConfig(extensionsToTreatAsEsm)} includes ${chalk.bold(
518+
"'.js'",
519+
)} which is always inferred based on ${chalk.bold(
520+
'type',
521+
)} in its nearest ${chalk.bold('package.json')}.`,
522+
);
523+
}
524+
525+
if (extensionsToTreatAsEsm.includes('.cjs')) {
526+
throw createConfigError(
527+
` Option: ${printConfig(extensionsToTreatAsEsm)} includes ${chalk.bold(
528+
"'.cjs'",
529+
)} which is always treated as CommonJS.`,
530+
);
531+
}
532+
533+
if (extensionsToTreatAsEsm.includes('.mjs')) {
534+
throw createConfigError(
535+
` Option: ${printConfig(extensionsToTreatAsEsm)} includes ${chalk.bold(
536+
"'.mjs'",
537+
)} which is always treated as an ECMAScript Module.`,
538+
);
539+
}
540+
}
541+
485542
export default function normalize(
486543
initialOptions: Config.InitialOptions,
487544
argv: Config.Argv,
@@ -583,6 +640,8 @@ export default function normalize(
583640
});
584641
}
585642

643+
validateExtensionsToTreatAsEsm(options.extensionsToTreatAsEsm);
644+
586645
const optionKeys = Object.keys(options) as Array<keyof Config.InitialOptions>;
587646

588647
optionKeys.reduce((newOptions, key: keyof Config.InitialOptions) => {
@@ -887,6 +946,7 @@ export default function normalize(
887946
case 'detectOpenHandles':
888947
case 'errorOnDeprecated':
889948
case 'expand':
949+
case 'extensionsToTreatAsEsm':
890950
case 'extraGlobals':
891951
case 'globals':
892952
case 'findRelatedTests':

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

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@@ -12,6 +12,7 @@ exports[`prints the config object 1`] = `
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"detectLeaks": false,
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"detectOpenHandles": false,
1414
"errorOnDeprecated": false,
15+
"extensionsToTreatAsEsm": [],
1516
"extraGlobals": [],
1617
"forceCoverageMatch": [],
1718
"globals": {},

‎packages/jest-jasmine2/src/index.ts

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149149
});
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151151
for (const path of config.setupFilesAfterEnv) {
152-
// TODO: remove ? in Jest 26
153-
const esm = runtime.unstable_shouldLoadAsEsm?.(path);
152+
const esm = runtime.unstable_shouldLoadAsEsm(
153+
path,
154+
config.extensionsToTreatAsEsm,
155+
);
154156

155157
if (esm) {
156158
await runtime.unstable_importModule(path);
@@ -163,9 +165,10 @@ async function jasmine2(
163165
const testNameRegex = new RegExp(globalConfig.testNamePattern, 'i');
164166
env.specFilter = (spec: Spec) => testNameRegex.test(spec.getFullName());
165167
}
166-
167-
// TODO: remove ? in Jest 26
168-
const esm = runtime.unstable_shouldLoadAsEsm?.(testPath);
168+
const esm = runtime.unstable_shouldLoadAsEsm(
169+
testPath,
170+
config.extensionsToTreatAsEsm,
171+
);
169172

170173
if (esm) {
171174
await runtime.unstable_importModule(testPath);

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