IntersectionObserverEntry.target

The IntersectionObserverEntry's target property specifies which Element previously targeted by calling IntersectionObserver.observe() experienced a change in intersection with the root.

In this simple example, each targeted element's opacity is set to its intersectionRatio.

function intersectionCallback(entries) {
  entries.forEach(function(entry) {
    entry.target.opacity = entry.intersectionRatio;
  });
}

To see a more concrete example, take a look at Handling intersection changes in Timing element visibility with the Intersection Observer API.