请问为什么我的代码这样写鼠标可以控制，可是键盘就控制不了呢？代码错在哪？怎么改
<!doctype html>
<html>
<head>
<meta charset="UTF-8">
<title>下拉菜单</title>
<style type="text/css">
body,
ul,
li {
margin: 0;
padding: 0;
font-size: 13px;
}
ul,
li {
list-style: none;
}
#divselect {
width: 186px;
margin: 80px auto;
position: relative;
z-index: 10000;
}
#divselect cite {
width: 150px;
height: 24px;
line-height: 24px;
display: block;
color: #807a62;
cursor: pointer;
font-style: normal;
padding-left: 4px;
padding-right: 30px;
border: 1px solid #333333;
background: url(xjt.png) no-repeat right center;
}
#divselect ul {
width: 184px;
border: 1px solid #333333;
background-color: #ffffff;
position: absolute;
z-index: 20000;
margin-top: -1px;
display: none;
}
#divselect ul li {
height: 24px;
line-height: 24px;
}
#divselect ul li a {
display: block;
height: 24px;
color: #333333;
text-decoration: none;
padding-left: 10px;
padding-right: 10px;
}
</style>
<script type="text/javascript">
window.onload = function() {
var box = document.getElementById('divselect'),
title = box.getElementsByTagName('cite')[0],
menu = box.getElementsByTagName('ul')[0],
as = box.getElementsByTagName('a'),
index = -1,
btn = false;
// 点击三角时
title.onclick = function(event) {
event = event || window.event;
if(event.stopPropagation) {
event.stopPropagation();
} else {
event.cancelBubble();
}
if(btn == false) {
menu.style.display = "block";
btn = true;
} else {
menu.style.display = "none";
btn = false;
}
// 键盘事件
document.onkeyup = function(event) {
e = event || window.event;
if(e.keyCode == 40) {
index++;
if(index >= as.length) {
index = 0;
}
changebgd();
}
if(e.keyCode == 38) {
if(index <= 0) {
index = as.length;
}
index--;
changebgd();
}
}
}
// 鼠标滑过、离开、点击每个选项时
for(var i = 0; i < as.length; i++) {
as[i].index = i;//得这样传值否则匿名函数获取不到i的值
as[i].onmouseover = function() {
for(var j = 0; j < as.length; j++) {
as[j].style.background = "none";
}
this.style.background = "#ccc";
index = this.index;
keyenter();
}
// as[i].onmouseout=function(){
// this.style.background="#fff";
// }上面那样写、键盘上下移动后鼠标移动，LI不存在两个“被选”。
as[i].onclick = function() {
title.innerHTML = this.innerHTML;
reset();
}
// 执行脚本
}
// 执行脚本
function changebgd() {
for(var i = 0; i < as.length; i++) {
as[i].style.background = "none";
}
as[index].style.background = "#ccc";
keyenter();
}
function keyenter() {
document.onkeyup = function(event) {
event = event || window.event;
if(event.keyCode == 13 && index != -1) {
title.innerHTML = as[index].innerHTML;
reset();
document.onkeyup=null;
}
}
}
// 点击页面空白处时
document.onclick = function() {
reset();
}
//复位函数
function reset() {
if(btn == true) {
if(index != -1) {
as[index].style.background = "none";
index = -1;
}
menu.style.display = "none";
btn = false;
}
}
// 执行脚本
}
</script>
</head>
<body>
<div id="divselect">
<cite>请选择分类</cite>
<ul>
<li id="li">
<a href="javascript:;" selectid="1">ASP开发</a>
</li>
<li>
<a href="javascript:;" selectid="2">.NET开发</a>
</li>
<li>
<a href="javascript:;" selectid="3">PHP开发</a>
</li>
<li>
<a href="javascript:;" selectid="4">Javascript开发</a>
</li>
<li>
<a href="javascript:;" selectid="5">Java特效</a>
</li>
</ul>
</div>
</body>
</html>
如果改，怎么个改法最好最少呢
