CSSTransition: transitionProperty property

.box {
  background-color: #165baa;
  color: white;
  width: 100px;
  height: 100px;
  transition: width 4s;
}
.box:hover {
  width: 200px;
}

const item = document.querySelector(".box");
item.addEventListener("transitionrun", () => {
  let animations = document.querySelector(".box").getAnimations();
  console.log(animations[0].propertyName);
});