test this point

index.js

@@ -109,7 +109,7 @@ const app=createApp({
         
         console.log("------  _books : "+_books);
         // console.log("------this.books : "+this.books);
-        // books.add(res[0]);
+        _books.add(res[0]);
       
         // console.log("------books : "+books);
         // console.log("------this : "+this);