Handle ERR_REQUIRE_ESM when reading configuration

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ### Features
 
+- `[jest-config]` Support ESM config files with `.js` extension ([#9573](https://github.com/facebook/jest/9573)).
 - `[jest-runtime]` Override `module.createRequire` to return a Jest-compatible `require` function ([#9469](https://github.com/facebook/jest/pull/9469))
 - `[*]` Support array of paths for `moduleNameMapper` aliases ([#9465](https://github.com/facebook/jest/pull/9465))
 

babel.config.js

@@ -35,7 +35,7 @@ module.exports = {
           },
         ],
       ],
-      test: 'packages/jest-config/src/importMjs.ts',
+      test: 'packages/jest-config/src/importEsm.ts',
     },
   ],
   plugins: [

e2e/__tests__/esmConfigFile.test.ts

@@ -35,4 +35,17 @@ onNodeVersions('^13.2.0', () => {
       name: 'Config from mjs file',
     });
   });
+
+  test('reads config from js file when package.json#type=module', () => {
+    const {json, exitCode} = runWithJson('esm-config/js', ['--show-config'], {
+      skipPkgJsonCheck: true,
+    });
+
+    expect(exitCode).toBe(0);
+    expect(json.configs).toHaveLength(1);
+    expect(json.configs[0].displayName).toEqual({
+      color: 'white',
+      name: 'Config from js file',
+    });
+  });
 });

e2e/esm-config/js/__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/js/jest.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.
+ */
+
+export default {
+  displayName: 'Config from js file',
+  testEnvironment: 'node',
+};

e2e/esm-config/js/package.json

@@ -0,0 +1,3 @@
+{
+  "type": "module"
+}

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

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

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

@@ -7,7 +7,7 @@
 
 import {readConfig} from '../index';
 
-jest.mock('../importMjs', () => (s: string) => import(s));
+jest.mock('../importEsm', () => (s: string) => import(s));
 
 test('readConfig() throws when an object is passed without a file path', async () => {
   await expect(

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

@@ -7,7 +7,7 @@
 
 import {readConfigs} from '../index';
 
-jest.mock('../importMjs', () => (s: string) => import(s));
+jest.mock('../importEsm', () => (s: string) => import(s));
 
 test('readConfigs() throws when called without project paths', async () => {
   await expect(

packages/jest-config/src/readConfigFileAndSetRootDir.ts

@@ -10,55 +10,49 @@ import * as fs from 'fs';
 import {Config} from '@jest/types';
 // @ts-ignore: vendored
 import jsonlint from './vendor/jsonlint';
-import {
-  JEST_CONFIG_EXT_JSON,
-  JEST_CONFIG_EXT_MJS,
-  PACKAGE_JSON,
-} from './constants';
-import importMjs from './importMjs';
+import {JEST_CONFIG_EXT_JSON, PACKAGE_JSON} from './constants';
+import importEsm from './importEsm';
 
 // 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.
+// 2. 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 isJSON = configPath.endsWith(JEST_CONFIG_EXT_JSON);
-  const isMjs = configPath.endsWith(JEST_CONFIG_EXT_MJS);
   let configObject;
 
-  if (isMjs) {
-    try {
-      const importedConfig = await importMjs(configPath);
+  try {
+    configObject = require(configPath);
+  } catch (error) {
+    if (error.code === 'ERR_REQUIRE_ESM') {
+      try {
+        const importedConfig = await importEsm(configPath);
 
-      if (!importedConfig.default) {
-        throw new Error(
-          `Jest: Failed to load mjs config file ${configPath} - did you use a default export?`,
-        );
-      }
+        if (!importedConfig.default) {
+          throw new Error(
+            `Jest: Failed to load mjs config file ${configPath} - did you use a default export?`,
+          );
+        }
 
-      configObject = importedConfig.default;
-    } catch (error) {
-      if (error.message === 'Not supported') {
-        throw new Error(
-          `Jest: Your version of Node does not support dynamic import - please enable it or use a .cjs file extension for file ${configPath}`,
-        );
-      }
+        configObject = importedConfig.default;
+      } catch (innerError) {
+        if (innerError.message === 'Not supported') {
+          throw new Error(
+            `Jest: Your version of Node does not support dynamic import - please enable it or use a .cjs file extension for file ${configPath}`,
+          );
+        }
 
-      throw error;
-    }
-  } else {
-    try {
-      configObject = require(configPath);
-    } catch (error) {
-      if (isJSON) {
-        throw new Error(
-          `Jest: Failed to parse config file ${configPath}\n` +
-            `  ${jsonlint.errors(fs.readFileSync(configPath, 'utf8'))}`,
-        );
-      } else {
-        throw error;
+        throw innerError;
       }
+    } else if (isJSON) {
+      throw new Error(
+        `Jest: Failed to parse config file ${configPath}\n` +
+          `  ${jsonlint.errors(fs.readFileSync(configPath, 'utf8'))}`,
+      );
+    } else {
+      throw error;
     }
   }
 

scripts/build.js

@@ -153,8 +153,8 @@ function buildFile(file, silent) {
             plugin[0],
             Object.assign({}, plugin[1], {
               lazy: string =>
-                // we want to lazyload all non-local modules plus `importMjs` - the latter to avoid syntax errors. Set to just `true` when we drop support for node 8
-                !string.startsWith('./') || string === './importMjs',
+                // we want to lazyload all non-local modules plus `importEsm` - the latter to avoid syntax errors. Set to just `true` when we drop support for node 8
+                !string.startsWith('./') || string === './importEsm',
             }),
           ];
         }