画圈重点：disabledDate的写法要用箭头函数，不能用普通函数写法，否则this指向就错了，会报                    undefined

 <el-date-picker v-model="time" type="date" value-format="yyyy-MM-dd" :picker-options="pickerOptions" placeholder="请选择" />

data(){
    return{
        signDate:'2023-10-11',
        pickerOptions: {
          disabledDate: (time) => {
             if (this.signDate) return time.getTime() < new Date(this.signDate).getTime();
             else return
          }
        }
    }
}