feat: add support for .mjs config

CHANGELOG.md

@@ -12,6 +12,7 @@
 - `[jest-config]` [**BREAKING**] Set default display name color based on runner ([#8689](https://github.com/facebook/jest/pull/8689))
 - `[jest-config]` Merge preset globals with project globals ([#9027](https://github.com/facebook/jest/pull/9027))
 - `[jest-config]` Support `.cjs` config files ([#9291](https://github.com/facebook/jest/pull/9291))
+- `[jest-config]` [**BREAKING**] Support `.mjs` config files ([#9431](https://github.com/facebook/jest/pull/9431))
 - `[jest-core]` Support reporters as default exports ([#9161](https://github.com/facebook/jest/pull/9161))
 - `[jest-core]` Support `--findRelatedTests` paths case insensitivity on Windows ([#8900](https://github.com/facebook/jest/issues/8900))
 - `[jest-diff]` Add options for colors and symbols ([#8841](https://github.com/facebook/jest/pull/8841))

babel.config.js

@@ -19,6 +19,22 @@ module.exports = {
       presets: ['@babel/preset-typescript'],
       test: /\.tsx?$/,
     },
+    // we want this file to keep `import()`, so exclude the transform for it
+    {
+      plugins: ['@babel/plugin-syntax-dynamic-import'],
+      presets: [
+        '@babel/preset-typescript',
+        [
+          '@babel/preset-env',
+          {
+            exclude: ['@babel/plugin-proposal-dynamic-import'],
+            shippedProposals: true,
+            targets: {node: 8},
+          },
+        ],
+      ],
+      test: 'packages/jest-config/src/importMjs.ts',
+    },
   ],
   plugins: [
     ['@babel/plugin-transform-modules-commonjs', {allowTopLevelThis: true}],

docs/Configuration.md

@@ -3,7 +3,7 @@ id: configuration
 title: Configuring Jest
 ---
 
-Jest's configuration can be defined in the `package.json` file of your project, or through a `jest.config.js` file or through the `--config <path/to/file.js|cjs|json>` option. If you'd like to use your `package.json` to store Jest's config, the "jest" key should be used on the top level so Jest will know how to find your settings:
+Jest's configuration can be defined in the `package.json` file of your project, or through a `jest.config.js` file or through the `--config <path/to/file.js|cjs|mjs|json>` option. If you'd like to use your `package.json` to store Jest's config, the `"jest"` key should be used on the top level so Jest will know how to find your settings:
 
 ```json
 {

e2e/__tests__/esmConfigFile.test.ts

@@ -0,0 +1,38 @@
+/**
+ * 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 {onNodeVersions} from '@jest/test-utils';
+import {json as runWithJson} from '../runJest';
+
+test('reads config from cjs file', () => {
+  const {json, exitCode} = runWithJson('esm-config/cjs', ['--show-config'], {
+    skipPkgJsonCheck: true,
+  });
+
+  expect(exitCode).toBe(0);
+  expect(json.configs).toHaveLength(1);
+  expect(json.configs[0].displayName).toEqual({
+    color: 'white',
+    name: 'Config from cjs file',
+  });
+});
+
+// not unflagged for other versions yet. Update this range if that changes
+onNodeVersions('^13.2.0', () => {
+  test('reads config from mjs file', () => {
+    const {json, exitCode} = runWithJson('esm-config/mjs', ['--show-config'], {
+      skipPkgJsonCheck: true,
+    });
+
+    expect(exitCode).toBe(0);
+    expect(json.configs).toHaveLength(1);
+    expect(json.configs[0].displayName).toEqual({
+      color: 'white',
+      name: 'Config from mjs file',
+    });
+  });
+});

e2e/esm-config/mjs/__tests__/test.js

@@ -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.
+ */
+
+test('dummy test', () => {
+  expect(1).toBe(1);
+});

e2e/esm-config/mjs/jest.config.mjs

@@ -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.
+ */
+
+export default {
+  displayName: 'Config from mjs file',
+  testEnvironment: 'node',
+};

e2e/esm-config/mjs/package.json

@@ -0,0 +1,3 @@
+{
+  "jest": {}
+}

packages/jest-cli/src/init/__tests__/__snapshots__/init.test.js.snap

@@ -36,6 +36,15 @@ Object {
 }
 `;
 
+exports[`init has-jest-config-file-mjs ask the user whether to override config or not user answered with "Yes" 1`] = `
+Object {
+  "initial": true,
+  "message": "It seems that you already have a jest configuration, do you want to override it?",
+  "name": "continue",
+  "type": "confirm",
+}
+`;
+
 exports[`init project with package.json and no jest config all questions answered with answer: "No" should return the default configuration (an empty config) 1`] = `
 "// For a detailed explanation regarding each configuration property, visit:
 // https://jestjs.io/docs/en/configuration.html

packages/jest-cli/src/init/__tests__/fixtures/has_jest_config_file_mjs/jest.config.mjs

@@ -0,0 +1,8 @@
+/**
+ * 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 default {};

packages/jest-cli/src/init/__tests__/fixtures/has_jest_config_file_mjs/package.json

@@ -0,0 +1 @@
+{}

packages/jest-cli/src/init/__tests__/fixtures/type_module/package.json

@@ -0,0 +1,7 @@
+{
+  "name": "type_module",
+  "scripts": {
+    "test": "different-test-runner"
+  },
+  "type": "module"
+}

packages/jest-cli/src/init/__tests__/init.test.js

@@ -9,8 +9,11 @@
 import * as fs from 'fs';
 import * as path from 'path';
 import prompts from 'prompts';
+import {constants} from 'jest-config';
 import init from '../';
-import {JEST_CONFIG_EXT_ORDER} from '../constants';
+import {onNodeVersions} from '@jest/test-utils';
+
+const {JEST_CONFIG_EXT_ORDER} = constants;
 
 jest.mock('prompts');
 jest.mock('../../../../jest-config/build/getCacheDirectory', () => () =>
@@ -52,6 +55,22 @@ describe('init', () => {
 
         expect(evaluatedConfig).toEqual({});
       });
+
+      onNodeVersions('^13.2.0', () => {
+        it('should generate empty config with mjs extension', async () => {
+          prompts.mockReturnValueOnce({});
+
+          await init(resolveFromFixture('type_module'));
+
+          const writtenJestConfigFilename = fs.writeFileSync.mock.calls[0][0];
+          const writtenJestConfig = fs.writeFileSync.mock.calls[0][1];
+
+          expect(writtenJestConfigFilename.endsWith('.mjs')).toBe(true);
+
+          expect(typeof writtenJestConfig).toBe('string');
+          expect(writtenJestConfig.split('\n')[3]).toBe('export default {');
+        });
+      });
     });
 
     describe('some questions answered with answer: "Yes"', () => {

packages/jest-cli/src/init/generate_config_file.ts

@@ -31,7 +31,10 @@ const stringifyOption = (
   );
 };
 
-const generateConfigFile = (results: Record<string, unknown>): string => {
+const generateConfigFile = (
+  results: Record<string, unknown>,
+  generateEsm = false,
+): string => {
   const {coverage, clearMocks, environment} = results;
 
   const overrides: Record<string, any> = {};
@@ -75,7 +78,7 @@ const generateConfigFile = (results: Record<string, unknown>): string => {
   return (
     '// For a detailed explanation regarding each configuration property, visit:\n' +
     '// https://jestjs.io/docs/en/configuration.html\n\n' +
-    'module.exports = {\n' +
+    (generateEsm ? 'export default {\n' : 'module.exports = {\n') +
     properties.join('\n') +
     '};\n'
   );

packages/jest-cli/src/init/index.ts

@@ -10,18 +10,20 @@ import * as path from 'path';
 import chalk = require('chalk');
 import prompts = require('prompts');
 import {sync as realpath} from 'realpath-native';
+import {constants} from 'jest-config';
 import defaultQuestions, {testScriptQuestion} from './questions';
 import {MalformedPackageJsonError, NotFoundPackageJsonError} from './errors';
-import {
+import generateConfigFile from './generate_config_file';
+import modifyPackageJson from './modify_package_json';
+import {ProjectPackageJson} from './types';
+
+const {
   JEST_CONFIG_BASE_NAME,
-  JEST_CONFIG_EXT_CJS,
+  JEST_CONFIG_EXT_MJS,
   JEST_CONFIG_EXT_JS,
   JEST_CONFIG_EXT_ORDER,
   PACKAGE_JSON,
-} from './constants';
-import generateConfigFile from './generate_config_file';
-import modifyPackageJson from './modify_package_json';
-import {ProjectPackageJson} from './types';
+} = constants;
 
 type PromptsResults = {
   clearMocks: boolean;
@@ -65,7 +67,7 @@ export default async (rootDir: string = realpath(process.cwd())) => {
       rootDir,
       getConfigFilename(
         projectPackageJson.type === 'module'
-          ? JEST_CONFIG_EXT_CJS
+          ? JEST_CONFIG_EXT_MJS
           : JEST_CONFIG_EXT_JS,
       ),
     );
@@ -131,7 +133,11 @@ export default async (rootDir: string = realpath(process.cwd())) => {
     console.log(`✏️  Modified ${chalk.cyan(projectPackageJsonPath)}`);
   }
 
-  const generatedConfig = generateConfigFile(results);
+  const generatedConfig = generateConfigFile(
+    results,
+    projectPackageJson.type === 'module' ||
+      jestConfigPath.endsWith(JEST_CONFIG_EXT_MJS),
+  );
 
   fs.writeFileSync(jestConfigPath, generatedConfig);
 

packages/jest-config/src/__tests__/Defaults.test.ts

@@ -7,6 +7,8 @@
 
 import {defaults} from '../index';
 
+jest.mock('../importMjs', () => (s: string) => import(s));
+
 test('get configuration defaults', () => {
   expect(defaults).toBeDefined();
 });

packages/jest-config/src/__tests__/readConfig.test.ts

@@ -7,16 +7,18 @@
 
 import {readConfig} from '../index';
 
-test('readConfig() throws when an object is passed without a file path', () => {
-  expect(() => {
+jest.mock('../importMjs', () => (s: string) => import(s));
+
+test('readConfig() throws when an object is passed without a file path', async () => {
+  await expect(
     readConfig(
       // @ts-ignore
       null /* argv */,
       {} /* packageRootOrConfig */,
       false /* skipArgvConfigOption */,
       null /* parentConfigPath */,
-    );
-  }).toThrowError(
+    ),
+  ).rejects.toThrowError(
     'Jest: Cannot use configuration as an object without a file path',
   );
 });

packages/jest-config/src/__tests__/readConfigs.test.ts

@@ -7,9 +7,11 @@
 
 import {readConfigs} from '../index';
 
-test('readConfigs() throws when called without project paths', () => {
-  expect(() => {
+jest.mock('../importMjs', () => (s: string) => import(s));
+
+test('readConfigs() throws when called without project paths', async () => {
+  await expect(
     // @ts-ignore
-    readConfigs(null /* argv */, [] /* projectPaths */);
-  }).toThrowError('jest: No configuration found for any project.');
+    readConfigs(null /* argv */, [] /* projectPaths */),
+  ).rejects.toThrowError('jest: No configuration found for any project.');
 });

packages/jest-config/src/constants.ts

@@ -13,10 +13,12 @@ export const DEFAULT_REPORTER_LABEL = 'default';
 export const PACKAGE_JSON = 'package.json';
 export const JEST_CONFIG_BASE_NAME = 'jest.config';
 export const JEST_CONFIG_EXT_CJS = '.cjs';
+export const JEST_CONFIG_EXT_MJS = '.mjs';
 export const JEST_CONFIG_EXT_JS = '.js';
 export const JEST_CONFIG_EXT_JSON = '.json';
 export const JEST_CONFIG_EXT_ORDER = Object.freeze([
   JEST_CONFIG_EXT_JS,
+  JEST_CONFIG_EXT_MJS,
   JEST_CONFIG_EXT_CJS,
   JEST_CONFIG_EXT_JSON,
 ]);

packages/jest-config/src/importMjs.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.
+ */
+
+// this is in a separate file so that node 8 don't explode with a syntax error.
+// Remove this file when we drop support for Node 8
+export default (specifier: string) => import(specifier);