//同时加载多个函数
function addLoadEvent(func){
	var oldLoad=window.onload;
	if(typeof oldLoad!="function"){
		window.onload=func;	
	}
	else{
		window.onload=function(){
			oldLoad();
			func();
		}	
	}
}
function $(o){ return document.getElementById(o);}
function $$(obj,str){ return $(obj).getElementsByTagName(str);}


//以下函数是实现菜单特效
addLoadEvent(menu);
//菜单效果
/*
obj   对象
element   标签元素
*/
var focusNum;
function $(obj,element) {return document.getElementById(obj).getElementsByTagName(element);}
function currentMenu(){//返回当前菜单项的下标数组
	var obj=$("topnav","a");
	//alert(typeof obj);
	//if(obj=="null") return false;
	for(var i=0;i<obj.length;i++){
		if(obj[i].className.indexOf("focus")!=-1){//如果包含该类
			focusNum=i;
			return focusNum;
		}
	}
}
function clearMenu(){//鼠标划出时所有的菜单都失去焦点
	var obj=$("topnav","a");
	for(var i=0;i<obj.length;i++){
		obj[i].className=obj[i].className.replace("focus","");
	}
}
function menu(){
	currentMenu();
	if(typeof focusNum=="undefined"){
		focusNum=00009;	
	};
	var obj=$("topnav","a");
	var obj_li=$("topnav","li");
	
	for(var i=0;i<obj.length;i++){
		obj[i].onmouseover=function(){
			clearMenu();
			this.className+=" focus";
		}
		obj[i].onmouseout=function(){
			this.className=this.className.replace("focus","");
				obj[focusNum].className+=" focus";
		}
	}
	
	for(var i=0;i<obj_li.length;i++){
		obj_li[i].onmouseover=function(){
			this.className+=" over";
		}
		obj_li[i].onmouseout=function() {
 			this.className=this.className.replace("over", "");
 		}
	}
}