[saosebastiao]

React, as it is presented to the programmer and for all practical reasoning, is programming with finite state machines. Sure, javascript is Turing complete and capable of much more (behind the scenes in React there is plenty going on that does not qualify as FSMs), and within a react application or even a component you might use Turing complete semantics to describe actions, data structures, effects, or whatever...but constrained to the API and idioms of react it is perfectly acceptable to call it FSM programming. In fact, Facebook already says this about react, that UIs are state machines and react is a way to declaratively describe them that way.

A better analogy for the equivalence of Finite State Machines and User Interfaces is the equivalence of human arms and levers. Just because it is one doesn't mean it isn't the other. One is abstract and the other is concrete, but there is still an equivalence. And not just computer user interfaces either...you could take pretty much any real world user interface: analog, mechanical, digital, whatever. Hell, tubas and vending machines are finite state machines. They fit the definition of a finite state machine because they are.