window .onload = function(){
	//获取class属性对象（样式名，该样式的对象tagName，父对象）
	var $cl = function(cl, objName, parentNodeObj) {
		var retnode = [];
		var myclass = new RegExp('\\b' + cl + '\\b');
		var elem = (parentNodeObj == null) ? document.getElementsByTagName(objName) : parentNodeObj.getElementsByTagName(objName);
		for (var j = 0; j < elem.length; j++) {
			var classes = elem[j].className;
			if (myclass.test(classes)) retnode.push(elem[j]);
		}
		return retnode;
	}
	var uls =document.getElementById("index_lb_ul");
	var lis = uls.getElementsByTagName("li");
	var bigPics = $cl("index_lb_bpic","a",uls);
	var bigTits = $cl("index_lb_btit","a",uls);
	var clearTime = null;
	var isScroll = true;//鼠标移入移出的切换开关
	var speed = 3000;
	var autoIndex = 0;
	for (var i = 0;i<lis.length;i++){
		lis.item(i).id= "li" +i.toString();
		lis.item(i).onmouseover = setTag;
		lis.item(i).onmouseout = setTag;
	}
	function showImg(index){
		for (var i = 0;i<bigPics.length; i++){
				lis.item(i).className = (i === index)? "index_lb_spic_hover":"";
				bigPics[i].style.display = (i === index)? "block":"none";
				bigTits[i].style.display = (i === index)? "block":"none";
		}
	}
	//切换图片
	function setTag(){
		var index = parseInt(this.id.replace("li","").toString());
		isScroll =!isScroll;
		if (isScroll){
			autoIndex =index;
			init();	
		}
		else{
			clearTimeout(clearTime);
			showImg(index);	
		}
	}
	//初始化
	function init(){
		showImg(autoIndex);
		if (autoIndex == lis.length-1){
				autoIndex = 0;	
			}
			else{
				autoIndex++
			}
		 clearTime = setTimeout(init,speed);
	}
	init();

}