Slider.vue

<template>
  <div class="item">
    <slot></slot>
  </div>
</template>

<script>
export default {
  data() {
    return {
      index: 0,
      show: false,
    }
  },
  computed: {
    show() {
      return this.$parent.index === this.index
    }
  },
  ready() {
    for (var c in this.$parent.$children) {
      if (this.$parent.$children[c] === this) {
          this.index = parseInt(c,10);
          break;
      }
    }
    //this.index = [...this.$el.parentNode.children].indexOf(this.$el)
    this.$parent.indicator.push(this.index)
    if (this.index === 0) {
      this.$el.classList.add('active')
    }
  }
}
</script>