自定义tap组件，无法获取event的值

WXML:

<view class="tabs">

    <view class="tabs_title">

        <view class="title_item  {{item.isActive?'active':''}}" 

        wx:for="{{tabs}}" 

        wx:key="id" 

        bindtab="itemTap" 

        data-index="{{index}}">

            {{item.value}}

        </view>

    </view>

    <view class="tabs_content" ></view>

</view>

JSON:

 methods: {

        itemTap(e){

            const {index} = e.currentTarget.dataset;

            console.log(index);

        }

    },