微信小程序表单验证错误提示效果

<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) 
  
 }, 
 
 ohShitfadeOut() { 
 var fadeOutTimeout = setTimeout(() => { 
  this.setData({ popErrorMsg: '' }); 
  clearTimeout(fadeOutTimeout); 
 }, 3000); 
 }, 
 
})