feat: Add support for the jest.config.ts configuration file

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ### Features
 
+- `[jest-cli, jest-config]` Add support for the `jest.config.ts` configuration file ([#10564](https://github.com/facebook/jest/pull/10564))
 - `[jest-circus, jest-config, jest-runtime]` Add new `injectGlobals` config and CLI option to disable injecting global variables into the runtime ([#10484](https://github.com/facebook/jest/pull/10484))
 - `[jest-each]` Fixes `.each` type to always be callable ([#10447](https://github.com/facebook/jest/pull/10447))
 - `[jest-runner]` Add support for `moduleLoader`s with `default` exports ([#10541](https://github.com/facebook/jest/pull/10541))

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|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:
+Jest's configuration can be defined in the `package.json` file of your project, or through a `jest.config.js`, or `jest.config.ts` file or through the `--config <path/to/file.js|ts|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
 {
@@ -31,6 +31,28 @@ module.exports = async () => {
 };
 ```
 
+Or through TypeScript:
+
+You can enable support for the TypeScript configuration file by installing the `ts-node` plugin in your project.
+
+```ts
+// jest.config.ts
+import type {Config} from '@jest/types';
+
+//Sync object
+const config: Config.InitialOptions = {
+  verbose: true,
+};
+export default config;
+
+//Or async function
+export default async (): Promise<Config.InitialOptions> => {
+  return {
+    verbose: true,
+  };
+};
+```
+
 Please keep in mind that the resulting configuration must be JSON-serializable.
 
 When using the `--config` option, the JSON file must not contain a "jest" key:

e2e/__tests__/__snapshots__/jest.config.ts.test.ts.snap

@@ -0,0 +1,36 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`traverses directory tree up until it finds jest.config 1`] = `
+  console.log
+<<REPLACED>>/jest.config.ts/some/nested/directory
+
+      at Object.log (__tests__/a-giraffe.js:3:27)
+
+`;
+
+exports[`traverses directory tree up until it finds jest.config 2`] = `
+PASS ../../../__tests__/a-giraffe.js
+  ✓ giraffe
+  ✓ abc
+`;
+
+exports[`traverses directory tree up until it finds jest.config 3`] = `
+Test Suites: 1 passed, 1 total
+Tests:       2 passed, 2 total
+Snapshots:   0 total
+Time:        <<REPLACED>>
+Ran all test suites.
+`;
+
+exports[`works with jest.config.ts 1`] = `
+PASS __tests__/a-giraffe.js
+  ✓ giraffe
+`;
+
+exports[`works with jest.config.ts 2`] = `
+Test Suites: 1 passed, 1 total
+Tests:       1 passed, 1 total
+Snapshots:   0 total
+Time:        <<REPLACED>>
+Ran all test suites.
+`;

e2e/__tests__/jest.config.ts.test.ts

@@ -0,0 +1,73 @@
+/**
+ * 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 * as path from 'path';
+import {wrap} from 'jest-snapshot-serializer-raw';
+import runJest from '../runJest';
+import {cleanup, extractSummary, writeFiles} from '../Utils';
+
+const DIR = path.resolve(__dirname, '../jest.config.ts');
+
+beforeEach(() => cleanup(DIR));
+afterAll(() => cleanup(DIR));
+
+test('works with jest.config.ts', () => {
+  writeFiles(DIR, {
+    '__tests__/a-giraffe.js': `test('giraffe', () => expect(1).toBe(1));`,
+    'jest.config.ts': `export default {testEnvironment: 'jest-environment-jsdom-fifteen', testRegex: '.*-giraffe.js'};`,
+    'package.json': '{}',
+  });
+
+  const {stderr, exitCode} = runJest(DIR, ['-w=1', '--ci=false']);
+  const {rest, summary} = extractSummary(stderr);
+  expect(exitCode).toBe(0);
+  expect(wrap(rest)).toMatchSnapshot();
+  expect(wrap(summary)).toMatchSnapshot();
+});
+
+test('traverses directory tree up until it finds jest.config', () => {
+  writeFiles(DIR, {
+    '__tests__/a-giraffe.js': `
+    const slash = require('slash');
+    test('giraffe', () => expect(1).toBe(1));
+    test('abc', () => console.log(slash(process.cwd())));
+    `,
+    'jest.config.ts': `export default {testEnvironment: 'jest-environment-jsdom-fifteen', testRegex: '.*-giraffe.js'};`,
+    'package.json': '{}',
+    'some/nested/directory/file.js': '// nothing special',
+  });
+
+  const {stderr, exitCode, stdout} = runJest(
+    path.join(DIR, 'some', 'nested', 'directory'),
+    ['-w=1', '--ci=false'],
+    {skipPkgJsonCheck: true},
+  );
+
+  // Snapshot the console.loged `process.cwd()` and make sure it stays the same
+  expect(
+    wrap(stdout.replace(/^\W+(.*)e2e/gm, '<<REPLACED>>')),
+  ).toMatchSnapshot();
+
+  const {rest, summary} = extractSummary(stderr);
+  expect(exitCode).toBe(0);
+  expect(wrap(rest)).toMatchSnapshot();
+  expect(wrap(summary)).toMatchSnapshot();
+});
+
+test('invalid JS in jest.config.ts', () => {
+  writeFiles(DIR, {
+    '__tests__/a-giraffe.js': `test('giraffe', () => expect(1).toBe(1));`,
+    'jest.config.ts': `export default i'll break this file yo`,
+    'package.json': '{}',
+  });
+
+  const {stderr, exitCode} = runJest(DIR, ['-w=1', '--ci=false']);
+  expect(stderr).toMatch(
+    'Error: Jest: Failed to parse the TypeScript config file ',
+  );
+  expect(exitCode).toBe(1);
+});

package.json

@@ -55,6 +55,7 @@
     "istanbul-lib-report": "^3.0.0",
     "istanbul-reports": "^3.0.0",
     "jest": "workspace:packages/jest",
+    "jest-environment-jsdom-fifteen": "^1.0.2",
     "jest-junit": "^11.0.1",
     "jest-runner-tsd": "^1.1.0",
     "jest-silent-reporter": "^0.2.1",
@@ -77,6 +78,7 @@
     "strip-ansi": "^6.0.0",
     "tempy": "^0.6.0",
     "throat": "^5.0.0",
+    "ts-node": "^9.0.0",
     "type-fest": "^0.16.0",
     "typescript": "^4.0.2",
     "which": "^2.0.1"

packages/jest-cli/src/__tests__/cli/args.test.ts

@@ -82,13 +82,13 @@ describe('check', () => {
   it('raises an exception if config is not a valid JSON string', () => {
     const argv = {config: 'x:1'} as Config.Argv;
     expect(() => check(argv)).toThrow(
-      'The --config option requires a JSON string literal, or a file path with one of these extensions: .js, .mjs, .cjs, .json',
+      'The --config option requires a JSON string literal, or a file path with one of these extensions: .js, .ts, .mjs, .cjs, .json',
     );
   });
 
   it('raises an exception if config is not a supported file type', () => {
     const message =
-      'The --config option requires a JSON string literal, or a file path with one of these extensions: .js, .mjs, .cjs, .json';
+      'The --config option requires a JSON string literal, or a file path with one of these extensions: .js, .ts, .mjs, .cjs, .json';
 
     expect(() => check({config: 'jest.configjs'} as Config.Argv)).toThrow(
       message,

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

@@ -45,6 +45,15 @@ Object {
 }
 `;
 
+exports[`init has-jest-config-file-ts 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_ts/jest.config.ts

@@ -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 = {};

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

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

packages/jest-config/package.json

@@ -9,6 +9,9 @@
   "license": "MIT",
   "main": "build/index.js",
   "types": "build/index.d.ts",
+  "peerDependencies": {
+    "ts-node": "^9.0.0"
+  },
   "dependencies": {
     "@babel/core": "^7.1.0",
     "@jest/test-sequencer": "^26.4.2",

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

@@ -81,7 +81,7 @@ describe.each(JEST_CONFIG_EXT_ORDER.slice(0))(
 
       writeFiles(DIR, {[relativeJestConfigPath]: ''});
 
-      // jest.config.js takes presedence
+      // jest.config.js takes precedence
 
       // absolute
       expect(

packages/jest-config/src/constants.ts

@@ -15,9 +15,11 @@ 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_TS = '.ts';
 export const JEST_CONFIG_EXT_JSON = '.json';
 export const JEST_CONFIG_EXT_ORDER = Object.freeze([
   JEST_CONFIG_EXT_JS,
+  JEST_CONFIG_EXT_TS,
   JEST_CONFIG_EXT_MJS,
   JEST_CONFIG_EXT_CJS,
   JEST_CONFIG_EXT_JSON,

packages/jest-config/src/index.ts

@@ -74,7 +74,7 @@ export async function readConfig(
     config.rootDir = config.rootDir || packageRootOrConfig;
     rawOptions = config;
     // A string passed to `--config`, which is either a direct path to the config
-    // or a path to directory containing `package.json` or `jest.config.js`
+    // or a path to directory containing `package.json`, `jest.config.js` or `jest.config.ts`
   } else if (!skipArgvConfigOption && typeof argv.config == 'string') {
     configPath = resolveConfigPath(argv.config, process.cwd());
     rawOptions = await readConfigFileAndSetRootDir(configPath);

packages/jest-config/src/readConfigFileAndSetRootDir.ts

@@ -9,22 +9,33 @@ import * as path from 'path';
 import {pathToFileURL} from 'url';
 import * as fs from 'graceful-fs';
 import type {Config} from '@jest/types';
+import {interopRequireDefault} from './utils';
 // @ts-expect-error: vendored
 import jsonlint from './vendor/jsonlint';
-import {JEST_CONFIG_EXT_JSON, PACKAGE_JSON} from './constants';
+import {
+  JEST_CONFIG_EXT_JSON,
+  JEST_CONFIG_EXT_TS,
+  PACKAGE_JSON,
+} from './constants';
 
 // Read the configuration and set its `rootDir`
 // 1. If it's a `package.json` file, we look into its "jest" property
-// 2. For any other file, we just require it. If we receive an 'ERR_REQUIRE_ESM'
+// 2. If it's a `jest.config.ts` file, we convert it in JS and we parse it
+// 3. For any other file, we just require it. If we receive an 'ERR_REQUIRE_ESM'
 //    from node, perform a dynamic import instead.
 export default async function readConfigFileAndSetRootDir(
   configPath: Config.Path,
 ): Promise<Config.InitialOptions> {
+  const isTS = configPath.endsWith(JEST_CONFIG_EXT_TS);
   const isJSON = configPath.endsWith(JEST_CONFIG_EXT_JSON);
   let configObject;
 
   try {
-    configObject = require(configPath);
+    if (isTS) {
+      configObject = loadTSConfigFile(configPath);
+    } else {
+      configObject = require(configPath);
+    }
   } catch (error) {
     if (error.code === 'ERR_REQUIRE_ESM') {
       try {
@@ -54,6 +65,11 @@ export default async function readConfigFileAndSetRootDir(
         `Jest: Failed to parse config file ${configPath}\n` +
           `  ${jsonlint.errors(fs.readFileSync(configPath, 'utf8'))}`,
       );
+    } else if (isTS) {
+      throw new Error(
+        `Jest: Failed to parse the TypeScript config file ${configPath}\n` +
+          `  ${error}`,
+      );
     } else {
       throw error;
     }
@@ -81,3 +97,31 @@ export default async function readConfigFileAndSetRootDir(
 
   return configObject;
 }
+
+// Load the TypeScript configuration
+const loadTSConfigFile = (configPath: Config.Path): Config.InitialOptions => {
+  let registerer;
+
+  // Register TypeScript compiler instance
+  try {
+    registerer = require('ts-node').register();
+  } catch (e) {
+    if (e.code === 'MODULE_NOT_FOUND') {
+      throw new Error(
+        `Jest: 'ts-node' is required for the TypeScript configuration files. Make sure it is installed\nError: ${e.message}`,
+      );
+    }
+
+    throw new Error(
+      `Jest: Could not register 'ts-node' to read the TypeScript file: ${configPath}`,
+    );
+  }
+
+  registerer.enabled(true);
+
+  const configObject = interopRequireDefault(require(configPath)).default;
+
+  registerer.enabled(false);
+
+  return configObject;
+};

packages/jest-config/src/utils.ts

@@ -248,3 +248,7 @@ export const getSequencer = (
     prefix: 'jest-sequencer-',
     rootDir,
   });
+
+// eslint-disable-next-line @typescript-eslint/explicit-module-boundary-types
+export const interopRequireDefault = (obj: any): {default: any} =>
+  obj && obj.__esModule ? obj : {default: obj};

website/versioned_docs/version-26.4/Configuration.md

@@ -4,7 +4,7 @@ title: Configuring Jest
 original_id: configuration
 ---
 
-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:
+Jest's configuration can be defined in the `package.json` file of your project, or through a `jest.config.js`, or `jest.config.ts` file or through the `--config <path/to/file.js|ts|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
 {
@@ -32,6 +32,28 @@ module.exports = async () => {
 };
 ```
 
+Or through TypeScript:
+
+You can enable support for the TypeScript configuration file by installing the `ts-node` plugin in your project.
+
+```ts
+// jest.config.ts
+import type {Config} from '@jest/types';
+
+//Sync object
+const config: Config.InitialOptions = {
+  verbose: true,
+};
+export default config;
+
+//Or async function
+export default async (): Promise<Config.InitialOptions> => {
+  return {
+    verbose: true,
+  };
+};
+```
+
 Please keep in mind that the resulting configuration must be JSON-serializable.
 
 When using the `--config` option, the JSON file must not contain a "jest" key: