1  export default (map, defaultState) => (currentState, action) => {
 2    const state = !currentState ? defaultState : currentState
 3  
 4    if (!action) {
 5      return state
 6    }
 7  
 8    return Object.keys(map).includes(action.type)
 9      ? map[action.type](state, action.payload)
10      : state
11  }