title: Trigger IntersectionObserver before in view
body: <p>I'm trying to do a simple infinite scroller, but I really can't get it to trigger BEFORE the footer on the page is visible. Is it possible?</p>
  <p>I thought setting the rootMargin would do it, but the observer function does not seem to get fired.</p>
  <p>I'm using VueJS. Here is part of the footer component:</p>
  <pre><code>      mounted () {
          this.observer = new IntersectionObserver(this.handleIntersect, {
            root: null,
            rootMargin: '500px 0px',
            threshold: 0,
          })
          this.observer.observe(this.$el)
        },
  
        destroyed () {
          this.observer?.disconnect()
        },
  
        methods: {
          handleIntersect ([entry]) {
            console.log('entry:', entry.boundingClientRect.top)
          }
        },
  </code></pre>