Fork from https://learn.javascript.ru/proxy#enumerate Fixed enumerate with ownKeys

<!DOCTYPE html>
<html>

<body>
  <script>
    'use strict';
    'use strict';
    
    let user = {
      name: "Ilya",
      surname: "Kantor",
      _version: 1,
      _secret: 123456
    };
    
    let proxy = new Proxy(user, {
      ownKeys: function (target) {
        let props = Object.keys(target).filter(function (prop) {
        return prop[0] != '_';
        });
    
      return props;
      }
    });
    
    // отфильтрованы свойства, начинающиеся с _
    for(let prop in proxy) {
      alert(prop); // Выведет свойства user: name, surname
    }
  </script>
</body>

</html>