module: move cjs type check behind flag

PR-URL: #29732
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: David Carlier <devnexen@gmail.com>
Reviewed-By: Jiawen Geng <technicalcute@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Jan Krems <jan.krems@gmail.com>
Reviewed-By: Gus Caplan <me@gus.host>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anto Aravinth <anto.aravinth.cse@gmail.com>

Author: guybedford

lib/internal/modules/cjs/loader.js

@@ -953,7 +953,7 @@ Module.prototype._compile = function(content, filename) {
 
 // Native extension for .js
 Module._extensions['.js'] = function(module, filename) {
-  if (filename.endsWith('.js')) {
+  if (experimentalModules && filename.endsWith('.js')) {
     const pkg = readPackageScope(filename);
     if (pkg && pkg.type === 'module') {
       throw new ERR_REQUIRE_ESM(filename);

test/es-module/test-esm-type-flag-errors.js

@@ -1,3 +1,4 @@
+// Flags: --experimental-modules
 'use strict';
 const common = require('../common');
 const assert = require('assert');