for-in.diff

 function* EnumerateObjectProperties(obj) {
   const visited = new Set();
-  for (const key of Reflect.ownKeys(obj)) {
+  const keys = Reflect.ownKeys(obj)
+      .filter(key => typeof key !== "symbol" && (key = Reflect.getOwnPropertyDescriptor(obj, key)) && key.enumerable);
+  for (const key of keys) {
-    if (typeof key === "symbol") continue;
     const desc = Reflect.getOwnPropertyDescriptor(obj, key);
     if (desc) {
       visited.add(key);
-      if (desc.enumerable) yield key;
+      yield key;
     }
   }
   const proto = Reflect.getPrototypeOf(obj);
   if (proto === null) return;
   for (const protoKey of EnumerateObjectProperties(proto)) {
     if (!visited.has(protoKey)) yield protoKey;
   }
 }