为什么这段代码是先执行alert("i'm "+this.className);再执行this.style.backgroundColor="yellow";我想要的效果是先背景改变，再跳出alert，点确认后又变回原来的背景，求指导，谢谢
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en">
<head>
<meta http-equiv="Content-Type" content="text/html;charset=UTF-8">
<title>Document</title>
<style>
*{
padding: 0;
margin: 0;
}
.id1
{
position: absolute;
background-color: red;
width: 200px;
height: 200px;
z-index: -1;
}
.id2
{
position: absolute;
background-color: blue;
width: 150px;
height: 150px;
top: 25px;
left: 25px;
}
.id3
{
position: absolute;
background-color: green;
width: 100px;
height: 100px;
top: 25px;
left: 25px;
}
</style>
<script>
function lightHight() {
this.style.backgroundColor="yellow";
alert("i'm "+this.className);
this.style.backgroundColor="";
// body...
}
window.onload=function(){
var divs=document.getElementsByTagName("div");
divs[0].addEventListener("click",lightHight);
divs[1].addEventListener("click",lightHight);
divs[2].addEventListener("click",lightHight);
} </script>
</head>
<body>
<div>
<div>
<div>
</div>
</div>
</div>
</body>
</html>
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