模拟select的代码

$(document).ready(function(){
var newSelect = $("#aa");
newSelect.click(function(e){
//如果没有class，即关闭状态，就展开
//打开状态就不需要处理，冒泡执行document.click
if(this.className == ""){
this.className = "open";
$(this.nextSibling).slideDown("fast");
e.stopPropagation();//阻止冒泡
}
});

//关闭收起
function closeSelect(obj){
$(obj.nextSibling).slideUp("fast",function(){
obj.className = "";
});
}
$(document).bind("click", function() {
closeSelect(newSelect[0]);
});
newSelect.next().click(function(e){
var src = e.target;

//如果有选中任何一项，取选中文字执行替换操作并改变样式，相当于select.onchange
//冒泡执行document.click关闭收起
if(src.tagName == "A"){
var PObj = src.parentNode;
PObj.previousSibling.innerHTML = src.innerHTML;
$(src).siblings().removeClass();
src.className = "current";
PObj.nextSibling.value = src.getAttribute("value");
}
});
});