treat modules with no extension as .js

Author: srolel

lib/internal/modules/esm/get_format.js

@@ -50,7 +50,7 @@ function defaultGetFormat(url, context, defaultGetFormatUnused) {
   } else if (parsed.protocol === 'file:') {
     const ext = extname(parsed.pathname);
     let format;
-    if (ext === '.js') {
+    if (!ext || ext === '.js') {
       format = getPackageType(parsed.href) === 'module' ? 'module' : 'commonjs';
     } else {
       format = extensionFormatMap[ext];