<textarea
                        placeholder="写评论"
                        maxlength="40"
                        @input="descInput"
                        v-model="orders"
                        onchange="this.value=this.value.substring(0, 40)"
                        onkeydown="this.value=this.value.substring(0, 40)"
                        onkeyup="this.value=this.value.substring(0, 40)">
                    </textarea>
                    <span>{{numbers}} / 40</span>
　
data(){
　　return{
　　　　addshow:false,
　　　　numbers:0,
　　　　orders:''
　　}
},




descInput(){
    var txtVal = this.orders.length;
    this.numbers = txtVal
},

　　转自：https://www.cnblogs.com/fanqiuzhuji/p/12689751.html