微信小程序表单验证form提交错误提示效果

<view class="ad_popError" wx:if="{{popErrorMsg}}">{{popErrorMsg}}</view>
<view class="ad_popFt">
<form bindsubmit="goDetail" >
  <textarea class="ad_popArea" bindinput="mentTxtFn" focus="{{isPopOpen}}" placeholder="请输入留言内容" placeholder-style="color:#;" name="textarea" />
 <view class="ad_popCout">
 <text class="one_star">你还可以输入</text>
 <text class="one_stars {{!!tips?'danger':''}}">{{mentTxtCount}}</text>
 <text class="one_star">字</text>
 </view>
 <button class="informBtn" form-type="submit">确认发布</button>
</form>
</view>

page{background: #f4f4f4;}
.ad_popHd{height: 76rpx; line-height: 76rpx; font-size: 32rpx;text-align: center; border-bottom: 1px solid #cdd1cd; padding: 0 20rpx;color: #202120;}
.ad_popFt{ margin: 20rpx ; margin-: 50rpx;}
.ad_popArea{ width: 708rpx; height:400rpx;font-size:30rpx;padding: 20rpx; box-sizing: border-box; -webkit-box-sizing: border-box; line-height: 40rpx; color: #333; background: #fff; }
.ad_popCout{ color: #969899; font-size: 24rpx; text-align: right; line-height: 58rpx; padding: 0 20rpx;}
.informBtn{background: #09bb07;color: #fff;font-size: 34rpx; margin-: 38rpx;height: 88rpx;}
.one_stars{color: #999;}
.one_star{font-size: 20rpx;color: #999;}
.danger{ color: #f64400;}
.ad_popError{ background: #de352d; color: #fff; height: 58rpx; line-height: 58rpx; font-size: 24rpx; text-align: center; position: absolute; left: 0; : 0; width: 100%; z-index:3;}

// pages/informLeaveMsg/informLeaveMsg.js
Page({
 
 /
  页面的初始数据
 /
 data: {
 
 },
 //确认发布
 goDetail:function(e){
 setTimeout(()=>{
  var subValue = e.detail.value.textarea
  console.log(subValue)
  if (subValue == null || subValue == "") {
  console.log("不能为空")
  this.setData(
   { popErrorMsg: "发布的留言内容不能为空" }
  ); 
  this.ohShitfadeOut(); 
  return;  
  }
  
 },100)
 
 },
//定时器提示框3秒消失
 ohShitfadeOut() {
 var fadeOutTimeout = setTimeout(() => {
  this.setData({ popErrorMsg: '' });
  clearTimeout(fadeOutTimeout);
 }, 3000);
 },
 
})