JavaScript模拟下拉菜单代码

优点：点击body区域同样可以隐藏下拉菜单，且不会和body已有的onclick事件冲突。
缺点：请大家指出，虚心接受！
运行框代码看似繁多，实属无奈，请下载附件，以便更好观察或修改~！

<!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=gb2312" /> 
<title>下拉菜单</title> 
<style type="text/css"> 
body{margin:20px auto;font-family:Arial, Helvetica, sans-serif;font-size:12px;width:950px;height:400px;border:solid 1px #aaa; position:relative;padding:10px;} 
ul{margin:0;padding:0;list-style:none;} 
.dropDownList{position:absolute;left:100px;top:100px;} 
/* .dropDownList div.dropdown select{display:none;}*/ 
.dropDownList div.dropdown{float:left;margin-right:50px;width:200px;} 
.dropDownList span{display:block;width:146px;height:26px;background:url(http://3.bp.blogspot.com/_bdBPvgEipxw/SRMUkLCdX0I/AAAAAAAAAP8/HgDXLapwpAw/s320/select.gif) left top no-repeat;line-height:26px;text-indent:12px;border:solid 1px #83BBD9;cursor:default;} 
.dropDownList span.over{background-position:left bottom;border-color:#B4C91A;} 
    .dropDownList ul{background:#eee;width:200px;display:none;} 
        .dropDownList ul li{height:20px;width:100%;padding:3px 0;text-indent:12px;cursor:default;} 
        .dropDownList ul li.over{background:#ccc;} 
    .dropDownList ul.show{display:block;} 
</style> 
</head> 
<body> 
<h1>JavaScript模拟下拉菜单，做的仓促，虚心接受批评。</h1> 
<form action="#" method="get"> 
 
     
        <select name="birthday"> 
            <option>请选择</option> 
            <option>1988</option> 
            <option>1989</option> 
        </select> 
        <span>请选择年份</span> 
        <ul></ul> 
     
     
        <select name="sex"> 
            <option>性别</option> 
            <option>男</option> 
            <option>女</option> 
        </select> 
        <span>请选择性别</span> 
        <ul></ul> 
     
     
        <select name="student"> 
            <option>幼儿班</option> 
            <option>小学</option> 
            <option>初中</option> 
        </select> 
        <span>请选择学历</span> 
        <ul></ul> 
     
 
</form> 
</body> 
</html> 
<script type="text/javascript"> 
// JavaScript Document 
var ____configArray; 
function __initDropDownList(configArray){ 
    //获取Select菜单 
    ____configArray=configArray; 
    var existArray=configArray.split("|"); 
    for(var i=0;i<existArray.length;i++){ 
        if(existArray[i].length<1){return;} 
        //根据参数分别获取div，并分别添加事件 
        var parentContainer=document.getElementById(existArray[i]); 
        if(!parentContainer){return;} 
        //获取下面的select，且获取其中的option 
        var selectObj=parentContainer.getElementsByTagName("select"); 
        if(selectObj.length<1){return;} 
        var optionArray=selectObj[0].getElementsByTagName("option"); 
        //获取option，并分别添加到各个li 
        var optionLength=optionArray.length; 
        for(var j=0;j<optionLength;j++){ 
            //获取ul，以便能够添加项目 
            var ulObj=parentContainer.getElementsByTagName("ul"); 
            if(ulObj.length<1){return;} 
            //获取span，以便能显示当前选择的项目 
            var spanObj=parentContainer.getElementsByTagName("span"); 
            if(spanObj.length<1){return;} 
            var liObj=document.createElement("li"); 
            var textNode=document.createTextNode(optionArray[j].firstChild.nodeValue) 
            liObj.appendChild(textNode); 
            liObj.setAttribute("currentIndex",j); 
            //给每个liObj添加事件 
            liObj.onclick=function(){ 
                selectCurrentItem(this.parentNode,this); 
            } 
            liObj.onmouseover=function(){this.className="over";} 
            liObj.onmouseout=function(){this.className="";} 
            ulObj[0].appendChild(liObj); 
            spanObj[0].onclick=function(event){ 
                //如果当前是显示的，就隐藏，反之亦然 
                showHiddenUl(this); 
            } 
            spanObj[0].onmouseover=function(){this.className='over';} 
            spanObj[0].onmouseout=function(){this.className="";}; 
            ulObj[0].onclick=function(){this.className="";} 
        } 
        parentContainer.onclick=function(event){ 
            if(!event){event=window.event;} 
                //阻止事件冒泡 
                event.cancelBubble=true; 
                var eventUlObj=this.getElementsByTagName("ul")[0]; 
                bodyClickHiddenUl(eventUlObj); 
        } 
    } 
} 
function selectCurrentItem(ulObj,currentObj){ 
    var parentObj=ulObj.parentNode; 
    var spanObj=parentObj.getElementsByTagName("span")[0]; 
    spanObj.firstChild.nodeValue=currentObj.firstChild.nodeValue; 
    var selectObj=parentObj.getElementsByTagName("select")[0]; 
    selectObj.selectedIndex=parseInt(currentObj.getAttribute("currentIndex")); 
} 
function showHiddenUl(currentObj){ 
    var parentNode=currentObj.parentNode; 
    var ulObj=parentNode.getElementsByTagName("ul")[0]; 
    if(ulObj.className==""){ 
        ulObj.className="show"; 
    }else{ 
        ulObj.className=""; 
    } 
} 
//点击body区域（非"下拉菜单"）隐藏菜单 
function addBodyClick(func) { 
    var bodyObj=document.getElementsByTagName("body")[0]; 
    var oldBodyClick = bodyObj.onclick; 
        if (typeof bodyObj.onclick != 'function') { 
            bodyObj.onclick = func; 
        } else { 
            bodyObj.onclick = function() { 
            oldBodyClick(); 
            func(); 
        } 
    } 
} 
//隐藏所有的UL 
function bodyClickHiddenUl(eventUlObj){ 
    var existArray=____configArray.split("|"); 
    for(var i=0;i<existArray.length;i++){ 
        if(existArray[i].length<1){return;} 
        //寻找所有UL并且隐藏 
        var parentContainer=document.getElementById(existArray[i]); 
        if(!parentContainer){return;} 
        var ulObj=parentContainer.getElementsByTagName("ul"); 
        if(eventUlObj!=ulObj[0]){ 
            ulObj[0].className=""; 
        } 
    } 
} 
var __dropDownList="dropDownList1|dropDownList2|dropDownList3"; 
__initDropDownList(__dropDownList); 
//添加这个可以确保点击body区域的时候 也可以隐藏菜单 
addBodyClick(bodyClickHiddenUl); 
</script>

[Ctrl+A 全选注:如需引入外部Js需刷新才能执行]