fix(@angular/build): warn and remove jsdom launcher when used with karma

packages/angular/build/src/builders/karma/application_builder.ts

@@ -361,6 +361,7 @@ async function collectEntrypoints(
   return getTestEntrypoints(testFiles, { projectSourceRoot, workspaceRoot: context.workspaceRoot });
 }
 
+// eslint-disable-next-line max-lines-per-function
 async function initializeApplication(
   options: KarmaBuilderOptions,
   context: BuilderContext,
@@ -508,6 +509,17 @@ async function initializeApplication(
     { promiseConfig: true, throwErrors: true },
   );
 
+  // Check for jsdom which does not support executing ESM scripts.
+  // If present, remove jsdom and issue a warning.
+  const updatedBrowsers = parsedKarmaConfig.browsers?.filter((browser) => browser !== 'jsdom');
+  if (parsedKarmaConfig.browsers?.length !== updatedBrowsers?.length) {
+    parsedKarmaConfig.browsers = updatedBrowsers;
+    context.logger.warn(
+      `'jsdom' does not support ESM code execution and cannot be used for karma testing.` +
+        ` The 'jsdom' entry has been removed from the 'browsers' option.`,
+    );
+  }
+
   // Remove the webpack plugin/framework:
   // Alternative would be to make the Karma plugin "smart" but that's a tall order
   // with managing unneeded imports etc..

packages/angular/build/src/builders/karma/index.ts

@@ -68,7 +68,7 @@ function getBaseKarmaOptions(
 
   // Convert browsers from a string to an array
   if (typeof options.browsers === 'string' && options.browsers) {
-    karmaOptions.browsers = options.browsers.split(',');
+    karmaOptions.browsers = options.browsers.split(',').map((browser) => browser.trim());
   } else if (options.browsers === false) {
     karmaOptions.browsers = [];
   }

packages/angular/build/src/builders/karma/tests/options/browsers_spec.ts

@@ -0,0 +1,33 @@
+/**
+ * @license
+ * Copyright Google LLC All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.dev/license
+ */
+
+import { execute } from '../../index';
+import { BASE_OPTIONS, KARMA_BUILDER_INFO, describeKarmaBuilder } from '../setup';
+
+describeKarmaBuilder(execute, KARMA_BUILDER_INFO, (harness, setupTarget) => {
+  describe('Option: "browsers"', () => {
+    it('should warn if jsdom is used', async () => {
+      await setupTarget(harness);
+
+      harness.useTarget('test', {
+        ...BASE_OPTIONS,
+        browsers: BASE_OPTIONS.browsers + ',jsdom',
+      });
+
+      const { result, logs } = await harness.executeOnce();
+      expect(result?.success).toBeTrue();
+      expect(logs).toContain(
+        jasmine.objectContaining({
+          message: jasmine.stringMatching(
+            `'jsdom' does not support ESM code execution and cannot be used for karma testing.`,
+          ),
+        }),
+      );
+    });
+  });
+});