getters and setters in component's reactive state

[s-p-b]

I'm curious if there's a standard or recommended way to have computed getters and setters inside a component's reactive state. What I mean by this is, if I define a function in a module to return a template for a button together with its own button state, what's the best way of deriving some value from its present state?

• Are getters actually supported in reactive stores? If I define one without a corresponding setter, I get a JavaScript error
• How does ArrowJS handle object methods, vs arrow methods, when wrapped in reactive stores?
• Are watchers intended for side-effects, or for derived state? The examples suggest they are for side-effects.

A specific example on the main Arrow-js page explaining how to build reusable components would be quite helpful.
Thanks! really love ArrowJS otherwise.