当transition事件完成时调用函数（移动端导航的动画消失效果）。
<!doctype html>
<html>
<head>
<meta charset="utf-8">
<style>
#d1 {
width:600px;
height:600px;
margin:100px auto;
border:1px solid;
}
#d2 {
width:300px;
height:300px;
margin:150px;
border-radius: 150px;
background: #ccc;
transition-duration: 2s;
}
</style>
</head>
<body>
<div id="d1">
<div id="d2"></div>
</div>
<script>
var d1 = document.getElementById("d1");
var d2 = document.getElementById("d2");
d1.onclick = function(){
d2.style.width = "150px";
d2.style.height = "150px";
d2.style.borderRadius = "75px";
d2.style.background = "green";
};
d2.addEventListener("transitionend",function(){
d2.style.display = "none";
})
</script>
</body>
</html>
原文：https://www.cnblogs.com/dayin1/p/11241637.html