feat: support named exports from CJS as named ESM imports (#10673)

Author: SimenB

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ### Features
 
+- `[jest-runtime]` Support named exports from CommonJS as named ES Module imports ([#10673](https://github.com/facebook/jest/pull/10673))
 - `[jest-validate]` Add support for `recursiveDenylist` option as an alternative to `recursiveBlacklist` ([#10236](https://github.com/facebook/jest/pull/10236))
 
 ### Fixes

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

@@ -2,7 +2,7 @@
 
 exports[`on node ^12.16.0 || >=13.7.0 runs test with native ESM 1`] = `
 Test Suites: 1 passed, 1 total
-Tests:       14 passed, 14 total
+Tests:       15 passed, 15 total
 Snapshots:   0 total
 Time:        <<REPLACED>>
 Ran all test suites.

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

@@ -20,6 +20,7 @@ import staticImportedStatefulWithQuery from '../stateful.mjs?query=1';
 import staticImportedStatefulWithAnotherQuery from '../stateful.mjs?query=2';
 /* eslint-enable */
 import {double} from '../index';
+import defaultFromCjs, {namedFunction} from '../namedExport.cjs';
 
 test('should have correct import.meta', () => {
   expect(typeof require).toBe('undefined');
@@ -137,3 +138,10 @@ test('varies module cache by query', () => {
   expect(staticImportedStatefulWithAnotherQuery()).toBe(2);
   expect(staticImportedStatefulWithAnotherQuery()).toBe(3);
 });
+
+test('supports named imports from CJS', () => {
+  expect(namedFunction()).toBe('hello from a named CJS function!');
+  expect(defaultFromCjs.default()).toBe('"default" export');
+
+  expect(Object.keys(defaultFromCjs)).toEqual(['namedFunction', 'default']);
+});

e2e/native-esm/namedExport.cjs

@@ -0,0 +1,9 @@
+/**
+ * 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.
+ */
+
+module.exports.namedFunction = () => 'hello from a named CJS function!';
+module.exports.default = () => '"default" export';

packages/jest-runtime/package.json

@@ -20,6 +20,7 @@
     "@jest/types": "^26.6.0",
     "@types/yargs": "^15.0.0",
     "chalk": "^4.0.0",
+    "cjs-module-lexer": "^0.4.2",
     "collect-v8-coverage": "^1.0.0",
     "exit": "^0.1.2",
     "glob": "^7.1.3",

packages/jest-runtime/src/index.ts

@@ -18,6 +18,8 @@ import {
   Module as VMModule,
 } from 'vm';
 import * as nativeModule from 'module';
+// @ts-expect-error
+import parseCjs = require('cjs-module-lexer');
 import type {Config, Global} from '@jest/types';
 import type {
   Jest,
@@ -474,9 +476,30 @@ class Runtime {
     // CJS loaded via `import` should share cache with other CJS: https://github.com/nodejs/modules/issues/503
     const cjs = this.requireModuleOrMock(from, modulePath);
 
+    const transformedCode = this._fileTransforms.get(modulePath);
+
+    let cjsExports: ReadonlyArray<string> = [];
+
+    if (transformedCode) {
+      const {exports} = parseCjs(transformedCode.code);
+
+      // @ts-expect-error
+      cjsExports = exports.filter(exportName => {
+        // we don't wanna respect any exports _names_ default as a named export
+        if (exportName === 'default') {
+          return false;
+        }
+        return Object.hasOwnProperty.call(cjs, exportName);
+      });
+    }
+
     const module = new SyntheticModule(
-      ['default'],
+      [...cjsExports, 'default'],
       function () {
+        cjsExports.forEach(exportName => {
+          // @ts-expect-error
+          this.setExport(exportName, cjs[exportName]);
+        });
         // @ts-expect-error: TS doesn't know what `this` is
         this.setExport('default', cjs);
       },

yarn.lock

@@ -5770,6 +5770,13 @@ __metadata:
   languageName: node
   linkType: hard
 
+"cjs-module-lexer@npm:^0.4.2":
+  version: 0.4.2
+  resolution: "cjs-module-lexer@npm:0.4.2"
+  checksum: 2b06d73648a4c1e468f235457205984d0a7f62daaf750fa163c4d6d0965e50998d609bf2b9693aad8b55498aad460a9c2ec758f73eb60b7f988faf0eb54f53b8
+  languageName: node
+  linkType: hard
+
 "class-utils@npm:^0.3.5":
   version: 0.3.6
   resolution: "class-utils@npm:0.3.6"
@@ -11850,6 +11857,7 @@ fsevents@^1.2.7:
     "@types/node": ^14.0.27
     "@types/yargs": ^15.0.0
     chalk: ^4.0.0
+    cjs-module-lexer: ^0.4.2
     collect-v8-coverage: ^1.0.0
     execa: ^4.0.0
     exit: ^0.1.2