<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title></title>
<style type="text/css">
#test{
width: 100px;
height: 100px;
border:3px solid red;
background: pink;
text-align: center;
font: 50px/200px "微软雅黑" ;
position: absolute;
left: 0;
right: 0;
bottom: 0;
top: 0;
margin: auto;
transition-property: width;
transition-duration: 9s;
transition-timing-function: inherit;
}
html{
height: 100%;
}
html body{
height: 60%;
border: 3px solid yellow;
margin-top: 100px;
}
body:hover #test{
transition-property: height;
width: 200px;
height: 200px;
}
</style>
</head>
<body>
<div id="test">
</div>
</body>
</html>
异步加载 确实没看懂这什么坑
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title></title>
<style type="text/css">
#test{
width: 10px;
height: 10px;
border:3px solid red;
background: pink;
text-align: center;
font: 50px/200px "微软雅黑" ;
position: absolute;
left: 0;
right: 0;
bottom: 0;
top: 0;
margin: auto;
transition-property: width;
transition-duration: 9s;
transition-timing-function: inherit;
}
html{
height: 100%;
}
html body{
height: 60%;
border: 3px solid yellow;
margin-top: 100px;
}
</style>
<script type="text/javascript">
//transition 在元素首次渲染还没有结束的情况下是不会触发的
var tst=document.querySelector("#test");
tst.style.width="300px";
</script>
</head>
<body>
<div id="test">
</div>
</body>
</html>
在元素首次渲染还没有结束的情况下是不会触发的
原文：https://www.cnblogs.com/hack-ing/p/11776750.html