viewport

add it to the data:
isInViewPort: false

listen for scroll event:
this.$eventHub.$on('scrolled', this.setViewPort);

action:
/**
   * is the element in view port
   *
   * @return bool
   */
  setViewPort() {
      let rect = this.$el.getBoundingClientRect();
let html = document.documentElement;

if (
  rect.top >= 0 &&
  rect.left >= 0 &&
  rect.bottom <= (window.innerHeight || html.clientHeight) &&
  rect.right <= (window.innerWidth || html.clientWidth)
) {
  this.isInViewPort = true;
}
  },