Get class size of object

[JS]

Given an object, is there a built in way to get the size of the 
class the object represents? The object may be instantiated with 
a derived instance of the object type, so using classInstanceSize 
doesn't work on the type of the object.

I can obviously go through the trouble of adding a class member 
and override it in all the derived classes. I saw tsize in object 
but 2.063 says it doesn't exist.