counter.js

const { createStore } = Redux;

/* Action creators */
function increment() {
  return {
    type: 'INCREMENT'
  };
}

function decrement() {
  return {
    type: 'DECREMENT'
  };
}

/* Reducer */
function counter(state = 0, action) {
  switch(action.type) {
    case 'INCREMENT':
      return state + 1;
    case 'DECREMENT':
      return state - 1;
    default:
      return state;
  }
}

/* Store */

const store = createStore(counter);

/* View */

store.subscribe(() => {
  console.log(store.getState());
});

/* Execução */

store.dispatch(increment());
store.dispatch(increment());
store.dispatch(decrement());
store.dispatch(increment());
store.dispatch(increment());
store.dispatch(decrement());