test: cover extensionless ESM with explicit module type

Author: inoway46

lib/internal/modules/cjs/loader.js

@@ -1930,12 +1930,13 @@ Module._extensions['.js'] = function(module, filename) {
       format = 'typescript';
     }
   } else if (path.extname(filename) === '') {
-    // Extensionless files skip the .js suffix check above. When type: commonjs
-    // is explicit, force commonjs format so ESM syntax surfaces as SyntaxError
-    // instead of silently delegating to ESM.
+    // Extensionless files skip the .js suffix check above. When type is explicit,
+    // follow it so ESM syntax surfaces as SyntaxError for commonjs instead of
+    // silently delegating to ESM.
     pkg = packageJsonReader.getNearestParentPackageJSON(filename);
-    if (pkg?.data?.type === 'commonjs') {
-      format = 'commonjs';
+    const typeFromPjson = pkg?.data?.type;
+    if (typeFromPjson === 'commonjs' || typeFromPjson === 'module') {
+      format = typeFromPjson;
     }
   }
   const { source, format: loadedFormat } = loadSource(module, filename, format);

test/es-module/test-extensionless-esm-type-commonjs.js

@@ -7,34 +7,63 @@ const tmpdir = require('../common/tmpdir');
 
 tmpdir.refresh();
 
-const dir = tmpdir.resolve('extensionless-esm-commonjs');
-fs.mkdirSync(dir, { recursive: true });
+const commonjsDir = tmpdir.resolve('extensionless-esm-commonjs');
+fs.mkdirSync(commonjsDir, { recursive: true });
 
 // package.json with type: commonjs
 fs.writeFileSync(
-  path.join(dir, 'package.json'),
+  path.join(commonjsDir, 'package.json'),
   '{\n  "type": "commonjs"\n}\n',
   'utf8'
 );
 
 // Extensionless executable with shebang + ESM syntax.
 // NOTE: Execute via process.execPath to avoid PATH/env differences.
-const scriptPath = path.join(dir, 'script'); // no extension
+const commonjsScriptPath = path.join(commonjsDir, 'script'); // no extension
 fs.writeFileSync(
-  scriptPath,
+  commonjsScriptPath,
   '#!/usr/bin/env node\n' +
     "console.log('script STARTED')\n" +
     "import { version } from 'node:process'\n" +
     'console.log(version)\n',
   'utf8'
 );
-fs.chmodSync(scriptPath, 0o755);
+fs.chmodSync(commonjsScriptPath, 0o755);
 
 spawnSyncAndAssert(process.execPath, ['./script'], {
-  cwd: dir,
+  cwd: commonjsDir,
   encoding: 'utf8',
 }, {
   status: 1,
   stderr: /.+/,
   trim: true,
 });
+
+const moduleDir = tmpdir.resolve('extensionless-esm-module');
+fs.mkdirSync(moduleDir, { recursive: true });
+
+// package.json with type: module
+fs.writeFileSync(
+  path.join(moduleDir, 'package.json'),
+  '{\n  "type": "module"\n}\n',
+  'utf8'
+);
+
+const moduleScriptPath = path.join(moduleDir, 'script'); // no extension
+fs.writeFileSync(
+  moduleScriptPath,
+  '#!/usr/bin/env node\n' +
+    "console.log('script STARTED')\n" +
+    "import { version } from 'node:process'\n" +
+    'console.log(version)\n',
+  'utf8'
+);
+fs.chmodSync(moduleScriptPath, 0o755);
+
+spawnSyncAndAssert(process.execPath, ['./script'], {
+  cwd: moduleDir,
+  encoding: 'utf8',
+}, {
+  stdout: /script STARTED[\s\S]*v\d+\./,
+  trim: true,
+});