javascript - 利用JS修改元素的位置属性，为什么style.left可行而style.top失效？
Q.想利用JS中的move函数实现小图的斜线下移，但是明明代码几乎一样，left的移动可以实现，top却怎么也动不了
<!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">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>台球桌</title>
<style type="text/css">
*{
padding:0;
margin:0;
}
p{
background:url(../PICTURE/table.JPG) no-repeat;
height:260px;
width:465px;
}
#ball{}
</style>
<script>
function init(){
var timer = setInterval("move()",50);
}
function move(){
var ball = document.getElementById("ball");
left = parseInt(ball.style.left);
left += 1;
top = parseInt(ball.style.top);
top += 1;
ball.style.left = left + "px";
ball.style.top = top + "px";
}
</script>
</head>
<body onload="init()">
<p>
<img src="../PICTURE/ball.png" id="ball" style="position:absolute;left:6px;top:5px;"/>
</p>
</body>
</html>
