computed: {
    ...mapGetters(['getNoticeNum']),
    msgNum: {
      get () {
        return this.getNoticeNum
      },
      set (val) {
        this.setNoticeNum(val)
      }
    }
  },
  // watch 监听msgNum的变化 实际就是在监听getNoticeNum
  watch: {
    msgNum (newVal, oldVal) {
      console.log('newVal', newVal)
    
    }
  },