Custom JS class error - function is not a member of the class

I'm trying to make a very basic Momento JS class, but when I call the functions within the class I get the error message storeState and applyState are not members of Momento.

Here's the code for my class

  class Memento

    var objectRotation : Quaternion;
    var objectPostion : Vector3;

    function storeState(player_Object : Transform)
        objectRotation = player_Object.rotation;
        objectPostion = player_Object.position;

    function applyState(player_Object : Transform)

        player_Object.rotation = objectRotation;
        player_Object.position = objectPostion;


I then call the functions Momento.storeState(transform object) or Momento.applyState(transform object), but then get the above errors - 'storeState' is not a member of 'Momento' and 'applyState' is not a member of 'Momento'

Any advice is appreciated.

The class is called Memento, but all your errors refer to Momento - could have two similar named classes, and using the wrong one?

because your class is called "Memento" and not "Momento", try Memento.storeState