perf: use esbuild to process .mjs files

e2e/jest.config.js

@@ -10,6 +10,7 @@ module.exports = {
     '<rootDir>/jest-globals',
     '<rootDir>/path-mapping',
     '<rootDir>/snapshot-serializers',
+    '<rootDir>/transform-mjs',
     '<rootDir>/with-babel',
   ],
 };

e2e/path-mapping/__tests__/path-mapping.ts

@@ -2,6 +2,7 @@ import { bar } from '@bar/bar-constant';
 
 test('path mapping should work without being affected by resolver', async () => {
   expect(bar).toBe(1);
+  // @ts-expect-error testing purpose
   await expect(import('@foo/foo-constant')).rejects.toMatchInlineSnapshot(
     `[Error: Cannot find module '@foo/foo-constant' from '__tests__/path-mapping.ts']`,
   );

e2e/transform-mjs/__tests__/transform-mjs.ts

@@ -0,0 +1,6 @@
+// @ts-expect-error TypeScript < 4.5 doesn't support `.mjs` import
+import * as foo from '../foo.mjs';
+
+test('should transform mjs files', async () => {
+  expect(foo.pi).toBeDefined();
+});

e2e/transform-mjs/foo.mjs

@@ -0,0 +1,3 @@
+const pi = 3.14
+
+export { pi }

e2e/transform-mjs/jest.config.js

@@ -0,0 +1,12 @@
+/** @type {import('ts-jest/dist/types').ProjectConfigTsJest} */
+module.exports = {
+  displayName: 'transform-mjs',
+  globals: {
+    'ts-jest': {
+      tsconfig: '<rootDir>/../tsconfig.json',
+    },
+  },
+  transform: {
+    '^.+\\.(ts|js|mjs|html)$': '<rootDir>/../../build/index.js',
+  },
+};

package.json

@@ -48,6 +48,7 @@
     "update-e2e": "node scripts/update-e2e-deps.js"
   },
   "dependencies": {
+    "esbuild": "0.13.12",
     "jest-environment-jsdom": "^27.0.0",
     "pretty-format": "^27.0.0",
     "ts-jest": "^27.0.0"

src/__tests__/__snapshots__/ng-jest-transformer.spec.ts.snap

@@ -0,0 +1,49 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`NgJestTransformer should process successfully a mjs file to CommonJS codes 1`] = `
+Array [
+  "
+      const pi = parseFloat(3.124);
+
+      export { pi };
+    ",
+  Object {
+    "format": "cjs",
+    "loader": "js",
+    "sourcemap": false,
+    "target": "es2015",
+  },
+]
+`;
+
+exports[`NgJestTransformer should process successfully a mjs file to CommonJS codes 2`] = `
+Array [
+  "
+      const pi = parseFloat(3.124);
+
+      export { pi };
+    ",
+  Object {
+    "format": "cjs",
+    "loader": "js",
+    "sourcemap": true,
+    "target": "es2016",
+  },
+]
+`;
+
+exports[`NgJestTransformer should process successfully a mjs file to CommonJS codes 3`] = `
+Array [
+  "
+      const pi = parseFloat(3.124);
+
+      export { pi };
+    ",
+  Object {
+    "format": "cjs",
+    "loader": "js",
+    "sourcemap": true,
+    "target": "es2015",
+  },
+]
+`;

src/__tests__/ng-jest-transformer.spec.ts

@@ -1,9 +1,20 @@
+import { transformSync } from 'esbuild';
+
 import { NgJestCompiler } from '../compiler/ng-jest-compiler';
 import { NgJestConfig } from '../config/ng-jest-config';
 import { NgJestTransformer } from '../ng-jest-transformer';
 
 const tr = new NgJestTransformer();
 
+jest.mock('esbuild', () => {
+  return {
+    transformSync: jest.fn().mockReturnValue({
+      code: 'bla bla',
+      map: JSON.stringify({ version: 1, sourceContent: 'foo foo' }),
+    }),
+  };
+});
+
 describe('NgJestTransformer', () => {
   test('should create NgJestCompiler and NgJestConfig instances', () => {
     // @ts-expect-error testing purpose
@@ -22,43 +33,26 @@ describe('NgJestTransformer', () => {
     expect(cs).toBeInstanceOf(NgJestConfig);
   });
 
-  test('should process successfully a mjs file with CommonJS mode', () => {
+  test.each([
+    {
+      tsconfig: {
+        sourceMap: false,
+      },
+    },
+    {
+      tsconfig: {
+        target: 'es2016',
+      },
+    },
+    {
+      tsconfig: {},
+    },
+  ])('should process successfully a mjs file to CommonJS codes', ({ tsconfig }) => {
     const result = tr.process(
       `
       const pi = parseFloat(3.124);
 
-      export default pi;
-    `,
-      'foo.mjs',
-      {
-        config: {
-          cwd: process.cwd(),
-          extensionsToTreatAsEsm: [],
-          testMatch: [],
-          testRegex: [],
-        },
-      } as any, // eslint-disable-line @typescript-eslint/no-explicit-any
-    );
-
-    expect(typeof result).toBe('object');
-    // @ts-expect-error `code` is a property of `TransformSource`
-    expect(result.code).toMatchInlineSnapshot(`
-      "\\"use strict\\";
-      Object.defineProperty(exports, \\"__esModule\\", { value: true });
-      const pi = parseFloat(3.124);
-      exports.default = pi;
-      //# sourceMappingURL=foo.mjs.js.map"
-    `);
-    // @ts-expect-error `map` is a property of `TransformSource`
-    expect(result.map).toBeDefined();
-  });
-
-  test('should process successfully a mjs file with ESM mode', () => {
-    const result = tr.process(
-      `
-      const pi = parseFloat(3.124);
-
-      export default pi;
+      export { pi };
     `,
       'foo.mjs',
       {
@@ -69,50 +63,20 @@ describe('NgJestTransformer', () => {
           testRegex: [],
           globals: {
             'ts-jest': {
-              useESM: true,
+              tsconfig,
             },
           },
         },
-        supportsStaticESM: true,
       } as any, // eslint-disable-line @typescript-eslint/no-explicit-any
     );
 
-    expect(typeof result).toBe('object');
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    expect((transformSync as unknown as jest.MockInstance<unknown, any>).mock.calls[0]).toMatchSnapshot();
+    // @ts-expect-error `code` is a property of `TransformSource`
+    expect(result.code).toBeDefined();
     // @ts-expect-error `code` is a property of `TransformSource`
-    expect(result.code).toMatchInlineSnapshot(`
-      "const pi = parseFloat(3.124);
-      export default pi;
-      //# sourceMappingURL=foo.mjs.js.map"
-    `);
-    // @ts-expect-error `map` is a property of `TransformSource`
     expect(result.map).toBeDefined();
-  });
-
-  test('should throw syntax error for mjs file with checkJs true', () => {
-    expect(() =>
-      tr.process(
-        `
-      const pi == parseFloat(3.124);
-
-      export default pi;
-    `,
-        'foo.mjs',
-        {
-          config: {
-            cwd: process.cwd(),
-            extensionsToTreatAsEsm: [],
-            testMatch: [],
-            testRegex: [],
-            globals: {
-              'ts-jest': {
-                tsconfig: {
-                  checkJs: true,
-                },
-              },
-            },
-          },
-        } as any, // eslint-disable-line @typescript-eslint/no-explicit-any
-      ),
-    ).toThrowError();
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    (transformSync as unknown as jest.MockInstance<unknown, any>).mockClear();
   });
 });

src/ng-jest-transformer.ts

@@ -2,6 +2,7 @@ import path from 'path';
 
 import type { TransformedSource } from '@jest/transform';
 import type { Config } from '@jest/types';
+import { transformSync } from 'esbuild';
 import { ConfigSet } from 'ts-jest/dist/config/config-set';
 import { TsJestTransformer } from 'ts-jest/dist/ts-jest-transformer';
 import type { ProjectConfigTsJest, TransformOptionsTsJest } from 'ts-jest/dist/types';
@@ -26,33 +27,19 @@ export class NgJestTransformer extends TsJestTransformer {
     const configSet = this._createConfigSet(transformOptions.config);
     /**
      * TypeScript < 4.5 doesn't support compiling `.mjs` file by default when running `tsc` which throws error
-     * ```
-     * File '/Users/ahn/ts-jest-only-example/foo.mjs' has an unsupported extension. The only supported extensions are
-     * '.ts', '.tsx', '.d.ts', '.js', '.jsx'.
-     * ```
-     * However, `transpileModule` API supports `.mjs` so we use it as a workaround.
      */
     if (path.extname(filePath) === '.mjs') {
-      const compilerOptions = configSet.parsedTsConfig.options;
-      const compilerModule = configSet.compilerModule;
-      const { outputText, sourceMapText, diagnostics } = compilerModule.transpileModule(fileContent, {
-        compilerOptions: {
-          ...compilerOptions,
-          module:
-            transformOptions.supportsStaticESM && configSet.useESM
-              ? compilerModule.ModuleKind.ES2020
-              : compilerModule.ModuleKind.CommonJS,
-        },
-        fileName: filePath,
-        reportDiagnostics: configSet.shouldReportDiagnostics(filePath),
+      const { target, sourceMap } = configSet.parsedTsConfig.options;
+      const { code, map } = transformSync(fileContent, {
+        loader: 'js',
+        format: 'cjs',
+        target: target === configSet.compilerModule.ScriptTarget.ES2015 ? 'es2015' : 'es2016',
+        sourcemap: sourceMap,
       });
-      if (diagnostics?.length) {
-        configSet.raiseDiagnostics(diagnostics, filePath);
-      }
 
       return {
-        code: outputText,
-        map: sourceMapText,
+        code,
+        map,
       };
     } else {
       return super.process(fileContent, filePath, transformOptions);