element-ui project front-end error date.getHours is not a function

Error:

Implementation: time per second

is added, and there will be an exception when editing, and the time cannot be changed
. I read that the reason is that I got a string and needed to convert it to a new Date, but I tried several times without success

                      <el-form-item label="结束时间" prop="showTime">
                            date-picker type="datetime" placeholder="选择公告结束显示时间" value-format="yyyy-MM-dd HH:mm:ss"
                                default-time="23:59:59" v-model="sysDoc.showTime" style="width: 420px;" />
                        </el-form-item>

 rules: {
                showTime: [
                    { type: 'string', required: true, message: '请选择公告结束显示时间', trigger: 'change' }
                ],
            },

need to be processed in watch monitoring?