Написав счетчик с Redux, как это работает

const INCREMENT = "INCREMENT"; // define a constant for increment action types
const DECREMENT = "DECREMENT"; // define a constant for decrement action types

// define the counter reducer which will increment or decrement the state based on the action it receives
const counterReducer = (state = 0, action) => {
  switch (action.type) {
    case INCREMENT:
      return state + 1;

    case DECREMENT:
      return state - 1;

    default:
      return state;
  }
};

// define an action creator for incrementing
const incAction = () => {
  return {
    type: INCREMENT
  };
};

// define an action creator for decrementing
const decAction = () => {
  return {
    type: DECREMENT
  };
};

// define the Redux store here, passing in your reducers
const store = Redux.createStore(counterReducer);
Kibet Immanuel Ng'eno