a.html

<div ref="container">
  <Card v-for="(card, i) of cards" ref="cards">
    <IntersectionObserver :getTarget="() => this.$refs.cards[i]" @intersect="liftCard" @disintersect="unliftCard" />
    ...
  </Card>
</div>


<!-- vs -->
<div ref="container">
  <IntersectionObserver :getTarget="() => this.$refs.cards" @intersect="liftOrUnliftCard" />
  <Card v-for="(card, i) of cards">
    ...
  </Card>
</div>


<script>
export default {
  methods: {
    liftOrUnliftCard (entries) {
      entries.filter(({ isIntersecting }) => isIntersecting).forEach(this.liftCard)
      entries.filter(({ isIntersecting }) => !isIntersecting).forEach(this.unliftCard)
    },
    liftCard () { /* lift the card */ },
    unliftCard () { /* unlift the card */ },
  },
}
</script>