not proved features of class properties

"The property name is not placed into User.prototype. Instead, it is created by new before calling the constructor, it’s a property of the object itself."

you are talking about some features of "class properties" but the example code doesn't show these features. I changed the example code to show that defining property out of the constructor method is different from defining method in class structure.

1-js/09-classes/01-class/article.md

@@ -318,6 +318,9 @@ class User {
 }
 
 new User().sayHi();
+
+alert(User.prototype.sayHi); // placed in User.prototype
+alert(User.prototype.name); // undefined, not placed in User.prototype
 ```
 
 The property `name` is not placed into `User.prototype`. Instead, it is created by `new` before calling the constructor, it's a property of the object itself.