So siehts ganz gut aus !

node_modules/core-js/library/modules/es6.reflect.prevent-extensions.js

@@ -0,0 +1,16 @@
+// 26.1.12 Reflect.preventExtensions(target)
+var $export = require('./_export');
+var anObject = require('./_an-object');
+var $preventExtensions = Object.preventExtensions;
+
+$export($export.S, 'Reflect', {
+  preventExtensions: function preventExtensions(target) {
+    anObject(target);
+    try {
+      if ($preventExtensions) $preventExtensions(target);
+      return true;
+    } catch (e) {
+      return false;
+    }
+  }
+});