// 代码整理：懒人之家 lanrenzhijia.com
var get = {
	byid: function(id) {
		return document.getelementbyid(id)
	},
	byclass: function(sclass, oparent) {
		var aclass = [];
		var reclass = new regexp("(^| )" + sclass + "( |$)");
		var aelem = this.bytagname("*", oparent);
		for (var i = 0; i < aelem.length; i++) reclass.test(aelem[i].classname) && aclass.push(aelem[i]);
		return aclass
	},
	bytagname: function(elem, obj) {
		return (obj || document).getelementsbytagname(elem)
	}
};
window.onload = function ()
{
	var onav = get.byid("nav");
	var ali = get.bytagname("li", onav);
	var asubnav = get.byclass("subnav", onav);
	var osubnav = oem = timer = null;
	var i = 0;
	
	for (i = 1; i < ali.length; i++)
	{
		ali[i].onmouseover = function ()
		{
			//隐藏所有子菜单
			for (i = 0; i < asubnav.length; i++)asubnav[i].style.display = "none";
			
			//获取该项下的子菜单
			osubnav = get.byclass("subnav", this)[0];
			
			//获取该项下的指示箭头
			oem = get.bytagname("em", this)[0];
			
			//显示该项下的子菜单
			osubnav.style.display = "block";
			
			//判断显示区域
			onav.offsetwidth - this.offsetleft > osubnav.offsetwidth ? 
			
			//如果在显示范围居左显示
			osubnav.style.left = this.offsetleft + "px" :
			
			//超出显示范围居右显示
			osubnav.style.right = 0;
			
			//计算指标箭头显示位置
			oem.style.left = this.offsetleft - osubnav.offsetleft + 50 + "px";
			cleartimeout(timer);
			
			//阻止事件冒泡
			osubnav.onmouseover = function (event)
			{
				(event || window.event).cancelbubble = true;
				cleartimeout(timer)
			}
		};
		
		ali[i].onmouseout = function ()
		{
			timer = settimeout(function () {
				osubnav.style.display = "none"
			},300)	
		}
	}
};