fix(js): generate correct jest config for --compiler=swc --js

packages/js/src/generators/library/__snapshots__/library.spec.ts.snap

@@ -0,0 +1,22 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`lib --unit-test-runner jest should generate test configuration with swc and js 1`] = `
+"/* eslint-disable */
+const { readFileSync } = require('fs')
+
+// Reading the SWC compilation config and remove the \\"exclude\\"
+// for the test files to be compiled by SWC
+const { exclude: _, ...swcJestConfig } = JSON.parse(
+  readFileSync(\`\${__dirname}/.lib.swcrc\`, 'utf-8')
+);
+module.exports = {
+  displayName: 'my-lib',
+  preset: '../../jest.preset.js',
+  transform: {
+    '^.+\\\\\\\\.[tj]s$': ['@swc/jest', swcJestConfig],
+  },
+  moduleFileExtensions: ['ts', 'js', 'html'],
+  coverageDirectory: '../../coverage/libs/my-lib'
+};
+"
+`;

packages/js/src/generators/library/files/jest-config/jest.config.__ext__

@@ -1,5 +1,5 @@
 /* eslint-disable */
-import { readFileSync } from 'fs';
+<% if(js) {%>const { readFileSync } = require('fs')<% } else { %>import { readFileSync } from 'fs';<% } %>
 
 // Reading the SWC compilation config and remove the "exclude"
 // for the test files to be compiled by SWC

packages/js/src/generators/library/library.spec.ts

@@ -719,6 +719,30 @@ describe('lib', () => {
       expect(readme).toContain('nx test my-lib');
     });
 
+    it('should generate test configuration with swc and js', async () => {
+      await libraryGenerator(tree, {
+        ...defaultOptions,
+        name: 'myLib',
+        unitTestRunner: 'jest',
+        compiler: 'swc',
+        js: true,
+      });
+
+      expect(tree.exists('libs/my-lib/tsconfig.spec.json')).toBeTruthy();
+      expect(tree.exists('libs/my-lib/jest.config.js')).toBeTruthy();
+      expect(tree.exists('libs/my-lib/src/lib/my-lib.spec.js')).toBeTruthy();
+
+      const projectConfig = readProjectConfiguration(tree, 'my-lib');
+      expect(projectConfig.targets.test).toBeDefined();
+
+      expect(tree.exists(`libs/my-lib/jest.config.js`)).toBeTruthy();
+      expect(
+        tree.read(`libs/my-lib/jest.config.js`, 'utf-8')
+      ).toMatchSnapshot();
+      const readme = tree.read('libs/my-lib/README.md', 'utf-8');
+      expect(readme).toContain('nx test my-lib');
+    });
+
     describe('--buildable', () => {
       it('should generate the build target', async () => {
         await libraryGenerator(tree, {

packages/js/src/generators/library/library.ts

@@ -289,9 +289,18 @@ function replaceJestConfig(
   options: NormalizedSchema,
   filesDir: string
 ) {
+  // the existing config has to be deleted otherwise the new config won't overwrite it
+  const existingJestConfig = joinPathFragments(
+    filesDir,
+    `jest.config.${options.js ? 'js' : 'ts'}`
+  );
+  if (tree.exists(existingJestConfig)) {
+    tree.delete(existingJestConfig);
+  }
+
   // replace with JS:SWC specific jest config
   generateFiles(tree, filesDir, options.projectRoot, {
-    tmpl: '',
+    ext: options.js ? 'js' : 'ts',
     js: !!options.js,
     project: options.name,
     offsetFromRoot: offsetFromRoot(options.projectRoot),