Support jest-preset.js files within Node modules.

.gitignore

@@ -5,6 +5,8 @@
 /examples/*/node_modules/
 
 /integration-tests/*/node_modules
+!/integration-tests/presets/json/node_modules
+!/integration-tests/presets/js/node_modules
 /integration-tests/transform/*/coverage
 /integration-tests/transform/*/node_modules
 

CHANGELOG.md

@@ -2,6 +2,8 @@
 
 ### Features
 
+* `[jest-config]` Support jest-preset.js files within Node modules
+  ([#6185](https://github.com/facebook/jest/pull/6185))
 * `[jest-cli]` Add `--detectOpenHandles` flag which enables Jest to potentially
   track down handles keeping it open after tests are complete.
   ([#6130](https://github.com/facebook/jest/pull/6130))

docs/Configuration.md

@@ -470,7 +470,16 @@ Specifies notification mode. Requires `notify: true`.
 Default: `undefined`
 
 A preset that is used as a base for Jest's configuration. A preset should point
-to an npm module that exports a `jest-preset.json` module on its top level.
+to an npm module that exports a `jest-preset.json` or `jest-preset.js` module at
+its top level.
+
+Presets may also be relative filesystem paths.
+
+```json
+{
+  "preset": "./node_modules/foo-bar/jest-preset.js"
+}
+```
 
 ### `projects` [array<string | ProjectConfig>]
 

integration-tests/__tests__/presets.test.js

@@ -0,0 +1,21 @@
+/**
+ * Copyright (c) 2014-present, Facebook, Inc. 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.
+ *
+ * @flow
+ */
+'use strict';
+
+const runJest = require('../runJest');
+
+test('supports json preset', () => {
+  const result = runJest('presets/json');
+  expect(result.status).toBe(0);
+});
+
+test('supports js preset', () => {
+  const result = runJest('presets/js');
+  expect(result.status).toBe(0);
+});

integration-tests/presets/js/__tests__/index.js

@@ -0,0 +1,11 @@
+/**
+ * Copyright (c) 2014-present, Facebook, Inc. 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.
+ */
+'use strict';
+
+test('load file mapped by js preset', () => {
+  expect(require('./test.foo')).toEqual(42);
+});

integration-tests/presets/js/package.json

@@ -0,0 +1,5 @@
+{
+  "jest": {
+    "preset": "jest-preset-js"
+  }
+}

integration-tests/presets/json/__tests__/index.js

@@ -0,0 +1,11 @@
+/**
+ * Copyright (c) 2014-present, Facebook, Inc. 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.
+ */
+'use strict';
+
+test('load file mapped by json preset', () => {
+  expect(require('./test.foo')).toEqual(42);
+});

integration-tests/presets/json/package.json

@@ -0,0 +1,5 @@
+{
+  "jest": {
+    "preset": "jest-preset-json"
+  }
+}

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

@@ -882,7 +882,7 @@ describe('preset', () => {
   beforeEach(() => {
     const Resolver = require('jest-resolve');
     Resolver.findNodeModule = jest.fn(name => {
-      if (name === 'react-native/jest-preset.json') {
+      if (name === 'react-native/jest-preset') {
         return '/node_modules/react-native/jest-preset.json';
       }
       return '/node_modules/' + name;
@@ -897,6 +897,24 @@ describe('preset', () => {
       }),
       {virtual: true},
     );
+    jest.mock(
+      '/node_modules/with-json-ext/jest-preset.json',
+      () => ({
+        moduleNameMapper: {
+          json: true,
+        },
+      }),
+      {virtual: true},
+    );
+    jest.mock(
+      '/node_modules/with-js-ext/jest-preset.js',
+      () => ({
+        moduleNameMapper: {
+          js: true,
+        },
+      }),
+      {virtual: true},
+    );
   });
 
   afterEach(() => {
@@ -943,6 +961,21 @@ describe('preset', () => {
     }).not.toThrow();
   });
 
+  test('searches for .json and .js preset files', () => {
+    const Resolver = require('jest-resolve');
+
+    normalize(
+      {
+        preset: 'react-native',
+        rootDir: '/root/path/foo',
+      },
+      {},
+    );
+
+    const options = Resolver.findNodeModule.mock.calls[0][1];
+    expect(options.extensions).toEqual(['.json', '.js']);
+  });
+
   test('merges with options', () => {
     const {options} = normalize(
       {
@@ -1032,7 +1065,7 @@ describe('preset without setupFiles', () => {
 
   beforeAll(() => {
     jest.doMock(
-      '/node_modules/react-foo/jest-preset.json',
+      '/node_modules/react-foo/jest-preset',
       () => {
         return {
           moduleNameMapper: {b: 'b'},
@@ -1044,7 +1077,7 @@ describe('preset without setupFiles', () => {
   });
 
   afterAll(() => {
-    jest.dontMock('/node_modules/react-foo/jest-preset.json');
+    jest.dontMock('/node_modules/react-foo/jest-preset');
   });
 
   it('should normalize setupFiles correctly', () => {

packages/jest-config/src/normalize.js

@@ -36,8 +36,8 @@ import DEPRECATED_CONFIG from './deprecated';
 import setFromArgv from './set_from_argv';
 import VALID_CONFIG from './valid_config';
 const ERROR = `${BULLET}Validation Error`;
-const JSON_EXTENSION = '.json';
-const PRESET_NAME = 'jest-preset' + JSON_EXTENSION;
+const PRESET_EXTENSIONS = ['.json', '.js'];
+const PRESET_NAME = 'jest-preset';
 
 const createConfigError = message =>
   new ValidationError(ERROR, message, DOCUMENTATION_NOTE);
@@ -64,17 +64,25 @@ const setupPreset = (
   let preset;
   const presetPath = replaceRootDirInPath(options.rootDir, optionsPreset);
   const presetModule = Resolver.findNodeModule(
-    presetPath.endsWith(JSON_EXTENSION)
+    presetPath.charAt(0) === '.'
       ? presetPath
       : path.join(presetPath, PRESET_NAME),
     {
       basedir: options.rootDir,
+      extensions: PRESET_EXTENSIONS,
     },
   );
 
   try {
     // $FlowFixMe
     preset = (require(presetModule): InitialOptions);
+
+    // Force re-evaluation to support multiple projects
+    try {
+      if (presetModule) {
+        delete require.cache[require.resolve(presetModule)];
+      }
+    } catch (e) {}
   } catch (error) {
     if (error instanceof SyntaxError) {
       throw createConfigError(