Counter with observable state

Counter.js

export default function createCounter() {
  
  let state = 0;
  let state$ = new Observable();
  
  function setState(newState) {
    state = newState;
    state$.next(state);
  }
  
  return {    
    get state() { return state },
    state$,
    increment() { setState(state + 1) },
    decrement() { setState(state - 1) },
  }
  
}