module: fix extensionless entry with explicit type=commonjs

lib/internal/modules/cjs/loader.js

@@ -1929,6 +1929,15 @@ Module._extensions['.js'] = function(module, filename) {
     } else {
       format = 'typescript';
     }
+  } else if (path.extname(filename) === '') {
+    // 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);
+    const typeFromPjson = pkg?.data?.type;
+    if (typeFromPjson === 'commonjs' || typeFromPjson === 'module') {
+      format = typeFromPjson;
+    }
   }
   const { source, format: loadedFormat } = loadSource(module, filename, format);
   // Function require shouldn't be used in ES modules when require(esm) is disabled.

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

@@ -0,0 +1,25 @@
+'use strict';
+
+const { spawnSyncAndAssert } = require('../common/child_process');
+const fixtures = require('../common/fixtures');
+
+const commonjsDir = fixtures.path('es-modules', 'extensionless-esm-commonjs');
+
+spawnSyncAndAssert(process.execPath, ['--no-experimental-detect-module', './script'], {
+  cwd: commonjsDir,
+  encoding: 'utf8',
+}, {
+  status: 1,
+  stderr: /.+/,
+  trim: true,
+});
+
+const moduleDir = fixtures.path('es-modules', 'extensionless-esm-module');
+
+spawnSyncAndAssert(process.execPath, ['--no-experimental-detect-module', './script'], {
+  cwd: moduleDir,
+  encoding: 'utf8',
+}, {
+  stdout: /script STARTED[\s\S]*v\d+\./,
+  trim: true,
+});

test/fixtures/es-modules/extensionless-esm-commonjs/package.json

@@ -0,0 +1,3 @@
+{
+  "type": "commonjs"
+}

test/fixtures/es-modules/extensionless-esm-commonjs/script

@@ -0,0 +1,4 @@
+#!/usr/bin/env node
+console.log('script STARTED')
+import { version } from 'node:process'
+console.log(version)

test/fixtures/es-modules/extensionless-esm-module/package.json

@@ -0,0 +1,3 @@
+{
+  "type": "module"
+}

test/fixtures/es-modules/extensionless-esm-module/script

@@ -0,0 +1,4 @@
+#!/usr/bin/env node
+console.log('script STARTED')
+import { version } from 'node:process'
+console.log(version)