花了几小时整理了一下代码，怎样用js实现鼠标选择和键盘操作下拉菜单，非常经典的案例实战。js实现在鼠标经过时,改变字体的颜色和背景,然后下拉菜单显示。一般情况下,下拉菜单处于隐藏的状态。
<!doctype html>
<html lang="en">
<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;}
#pselect{width:186px; margin:80px auto; position:relative; z-index:10000;}
#pselect 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;}
#pselect ul{width:184px;border:1px solid #333333; background-color:#ffffff; position:absolute; z-index:20000; margin-top:-1px; display:none;}
#pselect ul li{height:24px; line-height:24px;}
#pselect 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('pselect'),
title=box.getElementsByTagName('cite')[0],
menu=box.getElementsByTagName('ul')[0],
as=box.getElementsByTagName('a'),
index=-1;
// 点击三角时 // 执行脚本
//显示选项面板
title.onclick=function(event){
event = event || window.event;//控制浏览器兼容
//取消冒泡事件
if(event.stopPropagation){//非ie
event.stopPropagation();
}else{
event.cancleBubble = true;//ie
}
menu.style.display = "block";
document.onkeydown = function(e){
e = e || window.event;
if(e.keyCode == 38){//下键
index++;
if(index == as.length){
index = 0;
}
resetAs();
as[index].style.background = "#567";
}else if(e.keyCode == 40){//上键
index--;
if(index<0){
index = as.length - 1;
}
resetAs();
as[index].style.background = "#567";
}else if(e.keyCode == 13){ //enter键
e.preventDefault?e.preventDefault():e.returnValue = false;
title.innerHTML = as[index].innerHTML;
index = -1;
menu.style.display = "none";
resetAs();
}
}
}
/*重置所有选项的背景*/
function resetAs(){
for(var i = 0,l = as.length;i<l;i++){
as[i].style.background = "#FFF";
}
}
// 滑过滑过、离开、点击每个选项时
// 执行脚本
for(var i = 0;i<as.length;i++){
as[i].onmouseover = function(){
this.style.background = "#567";
};
as[i].onmouseout = function(){
this.style.background = "#FFF";
};
as[i].onclick = function(event){
//取消冒泡事件
if(event.stopPropagation){//非ie
event.stopPropagation();
}else{
event.cancleBubble = true;//ie
}
title.innerHTML = this.innerHTML;
menu.style.display = "none";
}
}
// 点击页面空白处时 隐藏选项面板
// 执行脚本
document.onclick = function(){
menu.style.display = "none";
}
}
</script>
</head>
<body>
<p id="pselect">
<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>
</p>
</body>
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