feat: experimental ES Modules support

Author: SimenB

CHANGELOG.md

@@ -2,6 +2,8 @@
 
 ### Features
 
+- `[jest-runtime, jest-jasmine2, jest-circus]` Experimental, limited ECMAScript Modules support ([#9772](https://github.com/facebook/jest/pull/9772))
+
 ### Fixes
 
 ### Chore & Maintenance

e2e/__tests__/__snapshots__/moduleNameMapper.test.ts.snap

@@ -36,7 +36,7 @@ FAIL __tests__/index.js
       12 | module.exports = () => 'test';
       13 | 
 
-      at createNoMappedModuleFoundError (../../packages/jest-resolve/build/index.js:540:17)
+      at createNoMappedModuleFoundError (../../packages/jest-resolve/build/index.js:545:17)
       at Object.require (index.js:10:1)
 `;
 
@@ -65,6 +65,6 @@ FAIL __tests__/index.js
       12 | module.exports = () => 'test';
       13 | 
 
-      at createNoMappedModuleFoundError (../../packages/jest-resolve/build/index.js:540:17)
+      at createNoMappedModuleFoundError (../../packages/jest-resolve/build/index.js:545:17)
       at Object.require (index.js:10:1)
 `;

e2e/__tests__/__snapshots__/nativeEsm.test.ts.snap

@@ -0,0 +1,9 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`on node ^12.16.0 || >=13.0.0 runs test with native ESM 1`] = `
+Test Suites: 1 passed, 1 total
+Tests:       2 passed, 2 total
+Snapshots:   0 total
+Time:        <<REPLACED>>
+Ran all test suites.
+`;

e2e/__tests__/nativeEsm.test.ts

@@ -0,0 +1,36 @@
+/**
+ * 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 {resolve} from 'path';
+import wrap from 'jest-snapshot-serializer-raw';
+import {onNodeVersions} from '@jest/test-utils';
+import runJest, {getConfig} from '../runJest';
+import {extractSummary} from '../Utils';
+
+const DIR = resolve(__dirname, '../native-esm');
+
+test('test config is without transform', () => {
+  const {configs} = getConfig(DIR);
+
+  expect(configs).toHaveLength(1);
+  expect(configs[0].transform).toEqual([]);
+});
+
+// The versions vm.Module was introduced
+onNodeVersions('^12.16.0 || >=13.0.0', () => {
+  test('runs test with native ESM', () => {
+    const {exitCode, stderr, stdout} = runJest(DIR, [], {
+      nodeOptions: '--experimental-vm-modules',
+    });
+
+    const {summary} = extractSummary(stderr);
+
+    expect(wrap(summary)).toMatchSnapshot();
+    expect(stdout).toBe('');
+    expect(exitCode).toBe(0);
+  });
+});

e2e/native-esm/__tests__/native-esm.test.js

@@ -0,0 +1,23 @@
+/**
+ * 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 {double} from '../index';
+
+test('should have correct import.meta', () => {
+  expect(typeof jest).toBe('undefined');
+  expect(import.meta).toEqual({
+    jest: expect.anything(),
+    url: expect.any(String),
+  });
+  expect(
+    import.meta.url.endsWith('/e2e/native-esm/__tests__/native-esm.test.js')
+  ).toBe(true);
+});
+
+test('should double stuff', () => {
+  expect(double(1)).toBe(2);
+});

e2e/native-esm/index.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.
+ */
+
+export function double(num) {
+  return num * 2;
+}

e2e/native-esm/package.json

@@ -0,0 +1,7 @@
+{
+  "type": "module",
+  "jest": {
+    "testEnvironment": "node",
+    "transform": {}
+  }
+}

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

@@ -77,9 +77,24 @@ const jestAdapter = async (
     }
   });
 
-  config.setupFilesAfterEnv.forEach(path => runtime.requireModule(path));
+  for (const path of config.setupFilesAfterEnv) {
+    const esm = runtime.unstable_shouldLoadAsEsm(path);
+
+    if (esm) {
+      await runtime.unstable_importModule(path);
+    } else {
+      runtime.requireModule(path);
+    }
+  }
+
+  const esm = runtime.unstable_shouldLoadAsEsm(testPath);
+
+  if (esm) {
+    await runtime.unstable_importModule(testPath);
+  } else {
+    runtime.requireModule(testPath);
+  }
 
-  runtime.requireModule(testPath);
   const results = await runAndTransformResultsToJestFormat({
     config,
     globalConfig,

packages/jest-jasmine2/src/index.ts

@@ -155,7 +155,15 @@ async function jasmine2(
       testPath,
     });
 
-  config.setupFilesAfterEnv.forEach(path => runtime.requireModule(path));
+  for (const path of config.setupFilesAfterEnv) {
+    const esm = runtime.unstable_shouldLoadAsEsm(path);
+
+    if (esm) {
+      await runtime.unstable_importModule(path);
+    } else {
+      runtime.requireModule(path);
+    }
+  }
 
   if (globalConfig.enabledTestsMap) {
     env.specFilter = (spec: Spec) => {
@@ -169,7 +177,14 @@ async function jasmine2(
     env.specFilter = (spec: Spec) => testNameRegex.test(spec.getFullName());
   }
 
-  runtime.requireModule(testPath);
+  const esm = runtime.unstable_shouldLoadAsEsm(testPath);
+
+  if (esm) {
+    await runtime.unstable_importModule(testPath);
+  } else {
+    runtime.requireModule(testPath);
+  }
+
   await env.execute();
 
   const results = await reporter.getResults();

packages/jest-resolve/package.json

@@ -21,6 +21,7 @@
     "browser-resolve": "^1.11.3",
     "chalk": "^3.0.0",
     "jest-pnp-resolver": "^1.2.1",
+    "read-pkg-up": "^7.0.1",
     "realpath-native": "^2.0.0",
     "resolve": "^1.15.1"
   },

packages/jest-resolve/src/index.ts

@@ -15,6 +15,7 @@ import isBuiltinModule from './isBuiltinModule';
 import defaultResolver, {clearDefaultResolverCache} from './defaultResolver';
 import type {ResolverConfig} from './types';
 import ModuleNotFoundError from './ModuleNotFoundError';
+import shouldLoadAsEsm, {clearCachedLookups} from './shouldLoadAsEsm';
 
 type FindNodeModuleConfig = {
   basedir: Config.Path;
@@ -100,6 +101,7 @@ class Resolver {
 
   static clearDefaultResolverCache(): void {
     clearDefaultResolverCache();
+    clearCachedLookups();
   }
 
   static findNodeModule(
@@ -129,6 +131,9 @@ class Resolver {
     return null;
   }
 
+  // unstable as it should be replaced by https://github.com/nodejs/modules/issues/393, and we don't want people to use it
+  static unstable_shouldLoadAsEsm = shouldLoadAsEsm;
+
   resolveModuleFromDirIfExists(
     dirname: Config.Path,
     moduleName: string,

packages/jest-resolve/src/shouldLoadAsEsm.ts

@@ -0,0 +1,65 @@
+/**
+ * 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 {dirname, extname} from 'path';
+// @ts-ignore: experimental, not added to the types
+import {SourceTextModule} from 'vm';
+import type {Config} from '@jest/types';
+import readPkgUp = require('read-pkg-up');
+
+const runtimeSupportsVmModules = typeof SourceTextModule === 'function';
+
+const cachedLookups = new Map<string, boolean>();
+
+export function clearCachedLookups(): void {
+  cachedLookups.clear();
+}
+
+export default function cachedShouldLoadAsEsm(path: Config.Path): boolean {
+  let cachedLookup = cachedLookups.get(path);
+
+  if (cachedLookup === undefined) {
+    cachedLookup = shouldLoadAsEsm(path);
+    cachedLookups.set(path, cachedLookup);
+  }
+
+  return cachedLookup;
+}
+
+// this is a bad version of what https://github.com/nodejs/modules/issues/393 would provide
+function shouldLoadAsEsm(path: Config.Path): boolean {
+  if (!runtimeSupportsVmModules) {
+    return false;
+  }
+
+  const extension = extname(path);
+
+  if (extension === '.mjs') {
+    return true;
+  }
+
+  if (extension === '.cjs') {
+    return false;
+  }
+
+  // this isn't correct - we might wanna load any file as a module (using synthetic module)
+  // do we need an option to Jest so people can opt in to ESM for non-js?
+  if (extension !== '.js') {
+    return false;
+  }
+
+  const cwd = dirname(path);
+
+  // TODO: can we cache lookups somehow?
+  const pkg = readPkgUp.sync({cwd, normalize: false});
+
+  if (!pkg) {
+    return false;
+  }
+
+  return pkg.packageJson.type === 'module';
+}

packages/jest-runner/src/runTest.ts

@@ -163,7 +163,15 @@ async function runTestInternal(
 
   const start = Date.now();
 
-  config.setupFiles.forEach(path => runtime!.requireModule(path));
+  for (const path of config.setupFiles) {
+    const esm = runtime.unstable_shouldLoadAsEsm(path);
+
+    if (esm) {
+      await runtime.unstable_importModule(path);
+    } else {
+      runtime.requireModule(path);
+    }
+  }
 
   const sourcemapOptions: sourcemapSupport.Options = {
     environment: 'node',

packages/jest-runtime/src/__mocks__/createRuntime.js

@@ -49,7 +49,15 @@ module.exports = async function createRuntime(filename, config) {
     Runtime.createResolver(config, hasteMap.moduleMap),
   );
 
-  config.setupFiles.forEach(path => runtime.requireModule(path));
+  for (const path of config.setupFiles) {
+    const esm = runtime.unstable_shouldLoadAsEsm(path);
+
+    if (esm) {
+      await runtime.unstable_importModule(path);
+    } else {
+      runtime.requireModule(path);
+    }
+  }
 
   runtime.__mockRootPath = path.join(config.rootDir, 'root.js');
   runtime.__mockSubdirPath = path.join(

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

@@ -93,9 +93,22 @@ export async function run(
 
     const runtime = new Runtime(config, environment, hasteMap.resolver);
 
-    config.setupFiles.forEach(path => runtime.requireModule(path));
+    for (const path of config.setupFiles) {
+      const esm = runtime.unstable_shouldLoadAsEsm(path);
 
-    runtime.requireModule(filePath);
+      if (esm) {
+        await runtime.unstable_importModule(path);
+      } else {
+        runtime.requireModule(path);
+      }
+    }
+    const esm = runtime.unstable_shouldLoadAsEsm(filePath);
+
+    if (esm) {
+      await runtime.unstable_importModule(filePath);
+    } else {
+      runtime.requireModule(filePath);
+    }
   } catch (e) {
     console.error(chalk.red(e.stack || e));
     process.on('exit', () => (process.exitCode = 1));