Stated Lib Base with deriveState

StatedLibBase.js

export default function createBase(initialState, deriveState){
  let state = deriveState ? deriveState(initialState) : initialState;
  let state$ = new Observable();

  function setState(newState) {
    state = deriveState ? deriveState(newState) : newState;
    state$.next(state);
  }

  function updateState(update) {
    setState({
      ...state,
      ...update,
    });
  }

  return {
    get state() {return state},
    state$,
    setState,
    updateState,
  };
  
}