LOOPING
=================
<div class="col-md-4 hidecontent" v-for="(item, index) in this.$parent.items" :key="item._id" :class="setClassName()" :content="['#data_' + index]">
    <div class="features_item sm-m-top-30">
        <div class="f_item_text">
            <img v-bind:src="item.picture">
            <span>{{ countTitle(item.title) }}</span>
            <p>{{ countSting(item.body) }}</p>
        </div>
    </div>
</div>

KONDISI YANG MAU DIPASANG (SETIAP 3 DATA)
=========================================
if(i % 3 === 2)

MAU DIPASANG DI METHOD TAPI MASIH GAGAL
=======================================
setClassName: function() {
    // this.intcount = 1
    if(this.intcount % 3 === 2) {
        this.output = 'data_'+this.intcount
        parseInt(this.intcount + 1)
    } else {
        this.output = 'data_'+this.intcount
    }
    return this.output
}

YANG DIINGINKAN
================
<div class="col-md-4 hidecontent data_1" content="#data_0">1 Blablablabla</div>
<div class="col-md-4 hidecontent data_1" content="#data_1">1 Blablablabla</div>
<div class="col-md-4 hidecontent data_1" content="#data_2">1 Blablablabla</div>
<div class="col-md-4 hidecontent data_2" content="#data_3">2 Blablablabla</div>
<div class="col-md-4 hidecontent data_2" content="#data_4">2 Blablablabla</div>
<div class="col-md-4 hidecontent data_2" content="#data_5">2 Blablablabla</div>
<div class="col-md-4 hidecontent data_3" content="#data_6">3 Blablablabla</div>
<div class="col-md-4 hidecontent data_3" content="#data_7">3 Blablablabla</div>
<div class="col-md-4 hidecontent data_3" content="#data_8">3 Blablablabla</div>