index.js

import { createStore } from "redux";

//const contador = document.getElementById("contador");
const decrementar = document.getElementById("decrementar");
const incrementar = document.getElementById("incrementar");

const INITIAL_STATE = {
  counter: 0
};

function counterApp(state = INITIAL_STATE, action) {
  console.log(state, action);
  switch (action.type){
    case 'INCREMENT':
      return {
        counter: state.counter + 1
      }
    case 'DECREMENT':
      return {
        counter: state.counter - 1
      }
    default:
      return state
  }
  return state;
}

const store = createStore(counterApp);
store.subscribe(()=>{
  const state = store.getState()
  //console.log('state changed', state)
  contador.innerText = state.counter
})

incrementar.addEventListener("click", () => {
  store.dispatch({ type: "INCREMENT" });
});

decrementar.addEventListener("click", () => {
  store.dispatch({ type: "DECREMENT" });
});