var childCreate = false;
function Offset(e) {
	//取标签的绝对位置
	var t = e.offsetTop;
	var l = e.offsetLeft;
	var w = e.offsetWidth;
	var h = e.offsetHeight - 2;
	while ( e = e.offsetParent) {
		t += e.offsetTop;
		l += e.offsetLeft;
	}
	return {
		top : t,
		left : l,
		width : w,
		height : h
	}
}

function loadselect(obj) {
	//第一步：取得select所在的位置
	var offset = Offset(obj);
	//第二步：将真的select隐藏
	obj.style.display = "none";
	//第三步：虚拟一个div出来代替select
	var iDiv = document.createElement("div");
	iDiv.id = "selectof" + obj.name;
	iDiv.style.position = "absolute";
	iDiv.style.width = offset.width + "px";
	iDiv.style.height = offset.height + "px";
	iDiv.style.top = offset.top + 4 + "px";
	iDiv.style.left = offset.left + 4 + "px";
	iDiv.style.background = "url('test.png') no-repeat right -6px";
	iDiv.style.border = "1px solid #ccc";
	iDiv.style.fontSize = "12px";
	iDiv.style.lineHeight = offset.height + "px";
	iDiv.style.textIndent = "4px";
	document.body.appendChild(iDiv);
	//第四步：将select中默认的选项显示出来
	var tValue = obj.options[obj.selectedIndex].innerHTML;
	iDiv.innerHTML = tValue;
	//第五步：模拟鼠标点击
	iDiv.style.background = "url('images/select.jpg') no-repeat right -2px";
	iDiv.onclick = function() {//鼠标点击
		if (document.getElementById("selectchild" + obj.name)) {
			//判断是否创建过div
			if (childCreate) {
				//判断当前的下拉是不是打开状态，如果是打开的就关闭掉。是关闭的就打开。
				document.getElementById("selectchild" + obj.name).style.display = "none";
				childCreate = false;
			} else {
				document.getElementById("selectchild" + obj.name).style.display = "";
				childCreate = true;
			}
		} else {
			//初始一个div放在上一个div下边，当options的替身。
			var cDiv = document.createElement("div");
			cDiv.id = "selectchild" + obj.name;
			cDiv.style.position = "absolute";
			cDiv.style.width = offset.width + "px";
			cDiv.style.height = obj.options.length * 20 + "px";
			cDiv.style.top = (offset.top + offset.height + 2) + 4+"px";
			cDiv.style.left = offset.left + 4+ "px";
			cDiv.style.background = "#f7f7f7";
			cDiv.style.border = "1px solid silver";
			var uUl = document.createElement("ul");
			uUl.id = "uUlchild" + obj.name;
			uUl.style.listStyle = "none";
			uUl.style.margin = "0";
			uUl.style.padding = "0";
			uUl.style.fontSize = "12px";
			cDiv.appendChild(uUl);
			document.body.appendChild(cDiv);
			childCreate = true;
			for (var i = 0; i < obj.options.length; i++) {
				//将原始的select标签中的options添加到li中
				var lLi = document.createElement("li");
				lLi.id = obj.options[i].value;
				lLi.style.textIndent = "4px";
				lLi.style.height = "20px";
				lLi.style.lineHeight = "20px";
				lLi.innerHTML = obj.options[i].innerHTML;
				uUl.appendChild(lLi);
			}
			var liObj = document.getElementById("uUlchild" + obj.name).getElementsByTagName("li");
			for (var j = 0; j < obj.options.length; j++) {
				//为li标签添加鼠标事件
				liObj[j].onmouseover = function() {
					this.style.background = "gray";
					this.style.color = "white";
				}
				liObj[j].onmouseout = function() {
					this.style.background = "white";
					this.style.color = "black";
				}
				liObj[j].onclick = function() {
					//做两件事情，一是将用户选择的保存到原始select标签中，要不做的再好看表单递交后也获取不到select的值了。
					obj.options.length = 0;
					obj.options[0] = new Option(this.innerHTML, this.id);
					//同时我们把下拉的关闭掉。
					document.getElementById("selectchild" + obj.name).style.display = "none";
					childCreate = false;
					iDiv.innerHTML = this.innerHTML;
				}
			}
		}
	}
}
document.body.onload = function (){
	var selects = document.getElementsByTagName("select");
	for(var i = 0 ; i < selects.length;i++){
		loadselect(selects[i]);
	}
}

?