效果图
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>demo</title>
<!-- <link rel="stylesheet" type="text/css" href="../css/demo4.css">
<script src="../js/demo4.js"></script> -->
<style type="text/css">
*{
margin: 0;
padding: 0;
}
#box{
width: 200px;
height: 200px;
margin: 0 auto;
background-color: #6cccf2;
opacity: 0.3;
}
</style>
<script type="text/javascript">
window.onload=function(){
var box = document.getElementById('box');
box.onmouseover=function(){
startChange(100);
};
box.onmouseout=function(){
startChange(30);
};
};
var timer = null;
function startChange(oTarget){
var speed = 0;
var box = document.getElementById('box');
var alpha = box.style.opacity*100;
if(alpha<oTarget){
speed=10;
}else if(alpha>oTarget){
speed= -10;
}
clearInterval(timer);
timer = setInterval(function(){
alpha = alpha + speed;
box.style.opacity = alpha/100;
if(alpha===oTarget){
clearInterval(timer);
}
},30);
}
</script>
</head>
<body>
<div class="wrap">
<div id="box"></div>
</div>
</body>
</html>