The IntersectionObserverEntry interface's read-only target property indicates which targeted Element has changed its amount of intersection with the intersection root.

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((entry) => {
    entry.target.style.opacity = entry.intersectionRatio;
  });
}

To see a more concrete example, take a look at Handling intersection changes.