如图：输入时到一定长度时统计不了正确长度？

  <textarea  maxlength='300'

        bindinput="bindTextAreaChange" value='{{commentContent}}' 

        cursor-spacing="100" bindfocus="changeFocusHeight" bindblur="clearFocusHeight">

        <view class="textNum" >

          <text>{{noteNowLen}}</text>/<text>300</text>

        </view>

 </textarea>

  bindTextAreaChange(e) {

    let commentContent = e.detail.value

 this.setData({

      commentContent,

      noteNowLen: commentContent.length

    })