# JavaScript Intersection Observer API
###### tags: `JavaScript`

let observer = new IntersectionObserver(
      entries => {
        if (entries[0].isIntersecting) {
          console.log("我出現了");
        } else {
          console.log("我消失了");
        }
        console.log(entries[0]);
      },
      {
        root: null
      }
    );
    observer.observe(document.getElementById("footer"));