countReducer.js

// redux-toolbelt action creator is imported directly to the reducer
import {increaseBy} from './actions'

export default countReducer = (state = deafaultState, {payload, type}) => {
  switch(type){
      
   // the action creator is used inside the reducer to get it's type
   case increaseBy.TYPE:
     return {
        ...state,
        count: state.count + payload
      }
      
    default: 
      return state
  }
}