js实现图片自动切换

<!DOCTYPE html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<style type="text/css">
*{margin:0;padding:0;list-style-type:none;}
body{font:12px/180% Arial, Helvetica, sans-serif, "宋体";color:#333;background:#f0f0f0;}
a,img{border:0;}
/* demo */
.demo{width:780px;margin:0 auto;}
.demo h2{height:70px;line-height:50px;font-size:22px;font-weight:normal;font-family:"Microsoft YaHei",SimHei;text-align:center;}
/* focus */
#focus{position:relative;width:780px;height:420px;overflow:hidden;}
#focus ul{height:420px;position:absolute;}
#focus ul li{float:left;width:780px;height:420px;overflow:hidden;position:relative;background:#000;}
#focus ul li div{position:absolute;overflow:hidden;}
#focus .btnBg{position:absolute;width:780px;height:40px;left:0;bottom:0;background:#000;}
#focus .btn{position:absolute;height:30px;left:10px;bottom:4px;}
#focus .btn span{
	float:left;display:inline-block;width:30px;height:30px;line-height:30px;text-align:center;font-size:16px;margin-right:10px;cursor:pointer;background:#716564;color:#ffffff;
	border-radius:15px;
	-moz-border-radius:15px;
	-webkit-border-radius:15px;
}
#focus .btn span.on{background:#B91919;color:#ffffff;}
</style>

<script type="text/javascript" src="http://code.jquery.com/jquery-1.9.1.js"></script>
<script type="text/javascript">
$(function(){
	var sWidth = $("#focus").width(); 
	var len = $("#focus ul li").length; 
	var index = 0;
	var picTimer;

	var btn = "<div class='btnBg'></div><div class='btn'>";
	for(var i=0; i < len; i++){
		btn += "<span>" + (i+1) + "</span>";
	}
	btn += "</div>"
	$("#focus").append(btn);
	$("#focus .btnBg").css("opacity",0.3);

	
	$("#focus .btn span").mouseenter(function(){
		index = $("#focus .btn span").index(this);
		showPics(index);
	}).eq(0).trigger("mouseenter");

	
	$("#focus ul").css("width",sWidth * (len + 1));

	
	$("#focus ul li div").hover(function(){
		$(this).siblings().css("opacity",0.7);
	},function() {
		$("#focus ul li div").css("opacity",1);
	});


	$("#focus").hover(function(){
		clearInterval(picTimer);
	},function(){
		picTimer = setInterval(function(){
			if(index == len){ 
				showFirPic();
				index = 0;
			}else{ 
				showPics(index);
			}
			index++;
		},3000); 
	}).trigger("mouseleave");

	
	function showPics(index){  
		var nowLeft = -index*sWidth;
		$("#focus ul").stop(true,false).animate({"left":nowLeft},500); 
		$("#focus .btn span").removeClass("on").eq(index).addClass("on"); 
	}

	function showFirPic(){ 
		$("#focus ul").append($("#focus ul li:first").clone());
		var nowLeft = -len*sWidth; 
		$("#focus ul").stop(true,false).animate({"left":nowLeft},500,function(){
			
			$("#focus ul").css("left","0");
			$("#focus ul li:last").remove();
		}); 
		$("#focus .btn span").removeClass("on").eq(0).addClass("on"); 
	}
	
});
</script>
</head>

<body>


<div class="demo">
	<h2>多格焦点图滚动切换</h2>
	<div id="focus">
		<ul>
			<li>
				<div style="left:0;top:0;"><a href="#"><img width="780" height="420" src="tupian_1.jpg"  /></a></div>
			</li>
			<li>
				<div style="left:0;top:0;"><a href="#"><img width="780" height="420" src="tupian_2.jpg" /></a></div>
				</li>
				<li>
				<div style="right:0;top:0;"><a href="#"><img width="780" height="420" src="tupian_3.jpg"  /></a></div>
				</li>
				<li>
				<div style="right:0;top:140px;"><a href="#"><img width="780" height="420" src="tupian_4.jpg"  /></a></div>
				</li>
				<li>
				<div style="right:0;bottom:0;"><a href="#"><img width="780" height="420" src="tupian_1.jpg"  /></a></div>
				</li>
			</li-->
			
		</ul>
	</div>
</div>
	
</body>
</html>