小米手机下滑图

<!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 type="text/css">
#demo{
512px;
height: 400px;
border: 1px solid red;
overflow: hidden;
margin: 100px auto;
position: relative;
}
#up{
512px;
height: 200px;
position: absolute;
top: 0;
cursor: pointer;
}
#down{
512px;
height: 200px;
position: absolute;
bottom: 0;
cursor: pointer;
}
#pic{
position: absolute;
top: 0;
}

</style>
<script type="text/javascript">
window.onload=function(){
function $(id){ return document.getElementById(id)}
var num = 0;
var timer = null;// 定时器名称
//鼠标经过上面框时，图片向上走
$("up").onmouseover = function(){
clearInterval(timer);
timer = setInterval(function(){
num -= 3;
//如果num大于等于-1070，图片继续一直向上走.
num >= -1070 ? $("pic").style.top = num +"px" : clearInterval(timer);
},30)
}
//鼠标经过下面框时，图片向下走
$("down").onmouseover = function(){
clearInterval(timer);
timer = setInterval(function(){
num ++;
num < 0 ? $("pic").style.top = num +"px" : clearInterval(timer);

},40)
}
}
</script>
</head>