module: handle extensionless entry with explicit type=commonjs

Author: inoway46

lib/internal/modules/cjs/loader.js

@@ -1929,6 +1929,14 @@ Module._extensions['.js'] = function(module, filename) {
     } else {
       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.
+    pkg = packageJsonReader.getNearestParentPackageJSON(filename);
+    if (pkg?.data?.type === 'commonjs') {
+      format = 'commonjs';
+    }
   }
   const { source, format: loadedFormat } = loadSource(module, filename, format);
   // Function require shouldn't be used in ES modules when require(esm) is disabled.