Adding a function on value_object

I don't think this is supported but thought it's worth asking.
```
value_object("PersonRecord")
.field("name", &PersonRecord::name)
.field("age", &PersonRecord::age)
;
```
Is it possible to add a function on a value_object? i.e on the JS side can we do `person.doSomething()`
Wondering if we could leverage `field` to make it callable.