iview DatePicker 回显验证报错

<FormItem label="入库时间:" prop="useTime">
        <DatePicker
          class="input-width"
          type="datetime"
          v-model="formValidate.useTime"
          placeholder="请选择入库时间"
          style=" 90%"
        />
      </FormItem>

//验证
ruleValidate：{
    useTime: [
          {
            type: "date", //这是关键
            required: true,
            message: "请输入入库时间",
            trigger: "blur"
          }
        ]
}

//编辑赋值做回显
this.formValidate.useTime = data.useTime; //data.useTime为2020-05-14 00:00:00

//保存赋值 得做转换
 this.formValidate.useTime = formatDate(
            new Date(this.formValidate.useTime).getTime(),
            "yyyy-MM-dd hh:mm:ss"
          );

//

formatDate 方法

export function formatDate(date, fmt = 'yyyy-MM-dd') {
  if (typeof (date) === 'number') {
    date = new Date(date)
  }
  var o = {
    "M+": date.getMonth() + 1, //月份
    "d+": date.getDate(), //日
    "h+": date.getHours(), //小时
    "m+": date.getMinutes(), //分
    "s+": date.getSeconds(), //秒
    "q+": Math.floor((date.getMonth() + 3) / 3), //季度
    "S": date.getMilliseconds() //毫秒
  }
  if (/(y+)/.test(fmt)) fmt = fmt.replace(RegExp.$1, (date.getFullYear() + "").substr(4 - RegExp.$1.length))
  for (var k in o)
    if (new RegExp("(" + k + ")").test(fmt))
      fmt = fmt.replace(RegExp.$1, (RegExp.$1.length == 1) ? (o[k]) : (("00" + o[k]).substr(("" + o[k]).length)))
  return fmt
}