redux中的reducer執(zhí)行減一操作

export default (state = initialState, action) => {
  const {total} = state
  switch(action.type){
    case ActionTypes.ADD:
      // 加
      return {...state, total: total + 1}
    case ActionTypes.SUBTRACT:
      // 減
      return {...state, total: total - 1}
    default:
      return state
  }
}

這里的return {...state, total: total - 1}和默認(rèn)返回的return state有什么區(qū)別,
...state起了什么作用