Constraining logic paths in JavaScript components

User interface components written for the Web typically have some state, some DOM binding mechanism and some logic controlling state changes, BUT the state change logic is typically defined ad-hoc rather than being encapsulated in explicit state machines that constrain state transitions.

Is there any value in defining/extracting explicit state machines for UI components or is it typically not worth the effort or complexity. It would seem that the state machines would have to be nested. Are there any libraries or idioms that might support explicit UI component state transition control on the Web?