SOURCE

function showMessage() {
    console.log('finished');    //过渡结束时触发打印log
}
var element = document.getElementById("tempDiv");
element.addEventListener("transitionend", showMessage, false);

<div id="tempDiv"></div>

#tempDiv {
  width:50px;
  height:50px;
    padding: 1px;
    transition-property: padding;
    transition-duration: 1s;
  background-color:#ddd;
}
#tempDiv:hover {
    padding: 5px;
}