小程序循环点击获取下标

<button hover="true" class="Itembtn" 
wx:for="{{zheng}}" 
wx:for-index="index" 
data-index="{{index}}" 
wx:for-item="item" 
bindtap="zhengzhuang" 
hover-class="btnhover">{{item.dosageUnit}}</button>
//其中wx:for="{{zheng}}"，zheng是从后台请求的数组，item.dosageUnit是数组中每一个元素，字段是dosageUnit

zhengzhuang: function (e) {
var that = this;
//获取下标
var idx = e.target.dataset.index;
console.log(idx)
}