fix(js): do not default to commonjs type field in package.json

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

@@ -977,6 +977,9 @@ describe('lib', () => {
         expect(config.targets.build.options.project).toEqual(
           `my-lib/package.json`
         );
+
+        const pkgJson = readJson(tree, 'my-lib/package.json');
+        expect(pkgJson.type).not.toBeDefined();
       });
 
       it('should always set compiler to swc if bundler is rollup', async () => {

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

@@ -869,10 +869,11 @@ function determineEntryFields(
       };
     case 'rollup':
       return {
-        type: 'commonjs',
+        // Since we're publishing both formats, skip the type field.
+        // Bundlers or Node will determine the entry point to use.
         main: './index.cjs',
         module: './index.js',
-        // typings is missing for rollup currently
+        typings: './src/index.d.ts',
       };
     case 'vite':
       return {
@@ -891,9 +892,9 @@ function determineEntryFields(
       };
     default: {
       return {
-        // CJS is the safest optional for now due to lack of support from some packages
-        // also setting `type: module` results in different resolution behavior (e.g. import 'foo' no longer resolves to 'foo/index.js')
-        type: 'commonjs',
+        // Safest option is to not set a type field.
+        // Allow the user to decide which module format their library is using
+        type: undefined,
       };
     }
   }