支持键盘方向键等按键的页面翻页跳转效果

<?
$n_id=$_GET['ID'];
$rs3=new COM("adodb.recordset");
$rs3->open("select top 1 * from [products2] where [id]<$n_id order by id desc",$conn,1,1);
if(! $rs3->eof)
{
echo "上一篇:<a href='?ID=".$rs3->Fields(id)->value."'>".$rs3->Fields(title)->value."</a>";
$prevpage="?ID=".$rs3->Fields(id)->value."";
}
else
{
echo "没有上一篇了";
}
?>
<BR>
<?
$rs2=new COM("adodb.recordset");
$rs2->open("select top 1 * from [Products2] where [id]>$n_id order by id asc",$conn,1,1);
if(! $rs2->eof)
{
echo "下一篇:<a href='?ID=".$rs2->Fields(id)->value."'>".$rs2->Fields(title)->value."</a>";
$nextpage="?ID=".$rs2->Fields(id)->value."";
}
else
{
echo "没有下一篇了";
}
?>

<script language=javascript>
document.onkeydown=nextpage
var prevpage="<?=$prevpage?>" //向左
var nextpage="<?=$nextpage?>" //向右
//var bookpage="http://www.aa25.cn" //回车
function nextpage(event)
{
 event = event ? event : (window.event ? window.event : null);

 //if (event.keyCode==13) location=bookpage;//回车
 if (event.keyCode==37) location=prevpage;//向左
 if (event.keyCode==39) location=nextpage;//向右
 //if (event.ctrlKey && event.keyCode==13) {alert("你点了 ctrl + enter ,现在转向到 标准之路."); location="http://www.aa25.cn";}
 //同时按下键盘多个键的事件情况
}
</script>