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__/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 +77,26 @@ const jestAdapter = async (
     }
   });
 
-  config.setupFilesAfterEnv.forEach(path => runtime.requireModule(path));
+  await Promise.all(
+    config.setupFilesAfterEnv.map(async path => {
+      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 +155,17 @@ async function jasmine2(
       testPath,
     });
 
-  config.setupFilesAfterEnv.forEach(path => runtime.requireModule(path));
+  await Promise.all(
+    config.setupFilesAfterEnv.map(async path => {
+      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 +179,14 @@ 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-runner/src/runTest.ts

@@ -67,6 +67,12 @@ function freezeConsole(
   };
 }
 
+function invariant(condition: unknown, message?: string): asserts condition {
+  if (!condition) {
+    throw new Error(message);
+  }
+}
+
 // Keeping the core of "runTest" as a separate function (as "runTestInternal")
 // is key to be able to detect memory leaks. Since all variables are local to
 // the function, when "runTestInternal" finishes its execution, they can all be
@@ -163,7 +169,19 @@ async function runTestInternal(
 
   const start = Date.now();
 
-  config.setupFiles.forEach(path => runtime!.requireModule(path));
+  await Promise.all(
+    config.setupFiles.map(async path => {
+      invariant(runtime, 'TS is being difficult');
+
+      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/package.json

@@ -38,6 +38,7 @@
     "jest-snapshot": "^25.3.0",
     "jest-util": "^25.3.0",
     "jest-validate": "^25.3.0",
+    "read-pkg-up": "^7.0.1",
     "realpath-native": "^2.0.0",
     "slash": "^3.0.0",
     "strip-bom": "^4.0.0",

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

@@ -49,7 +49,17 @@ module.exports = async function createRuntime(filename, config) {
     Runtime.createResolver(config, hasteMap.moduleMap),
   );
 
-  config.setupFiles.forEach(path => runtime.requireModule(path));
+  await Promise.all(
+    config.setupFiles.map(async path => {
+      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 +93,24 @@ export async function run(
 
     const runtime = new Runtime(config, environment, hasteMap.resolver);
 
-    config.setupFiles.forEach(path => runtime.requireModule(path));
+    await Promise.all(
+      config.setupFiles.map(async path => {
+        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));