为什么我的offsetLeft每次加9px
<!doctype>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html;charset=UTF-8">
<title>透明度动画</title>
<style type="text/css">
#wrap{width:230px;height:105px;position: relative;left:-217px;}
#red{width:200px;height:100px;background-color: red;position: absolute;}
#blue{width:30px;height:30px;background-color: blue;margin-left: 200px;position: absolute;}
</style>
<script type="text/javascript">
window.onload=function(){
var wrap=document.getElementById("wrap");
var timer=null
wrap.onmouseover=function(){
startMove();
}
}
function startMove(){
timer=setInterval(function(){
if(wrap.offsetLeft==0){
clearInterval(timer);
}
else{
wrap.style.left=wrap.offsetLeft+1+'px'; //console.log(wrap.offsetLeft);
}
},300);
}
</script>
</head>
<body>
<div id="wrap">
<div id="red"></div>
<div id="blue"></div>
</div>
</body>
</html>
为什么我的offsetLeft每次加9px
