如何利用html+css+JavaScript來實現簡單的圖片切換特效

<p class="wrapper"> 
<p id="focus"> 
<ul> 
<li><a href="http://www.lanrentuku.com/" target="_blank"><img src="img/01.jpg" alt="QQ商城焦点图效果下载" /></a></li> 
<li><a href="http://www.lanrentuku.com/" target="_blank"><img src="img/02.jpg" alt="QQ商城焦点图效果教程" /></a></li> 
<li><a href="http://www.lanrentuku.com/" target="_blank"><img src="img/03.jpg" alt="jquery商城焦点图效果" /></a></li> 
<li><a href="http://www.lanrentuku.com/" target="_blank"><img src="img/04.jpg" alt="jquery商城焦点图代码" /></a></li> 
<li><a href="http://www.lanrentuku.com/" target="_blank"><img src="img/05.jpg" alt="jquery商城焦点图源码" /></a></li> 
</ul> 
</p> 
</p><!-- wrapper end --> 
</body>

<style type="text/css"> 
* {margin:0; padding:0;} 
body {font-size:12px; color:#222; font-family:Verdana,Arial,Helvetica,sans-serif; background:#f0f0f0;} 
.clearfix:after {content: "."; display: block; height: 0; clear: both; visibility: hidden;} 
.clearfix {zoom:1;} 
ul,li {list-style:none;} 
img {border:0;} 

.wrapper {width:800px; margin:0 auto; padding-bottom:50px;} 

/* qqshop focus */ 
#focus {width:800px; height:280px; overflow:hidden; position:relative;} 
#focus ul {height:380px; position:absolute;} 
#focus ul li {float:left; width:800px; height:280px; overflow:hidden; position:relative; background:#000;} 
#focus ul li p {position:absolute; overflow:hidden;} 
#focus .btnBg {position:absolute; width:800px; height:20px; left:0; bottom:0; background:#000;} 
#focus .btn {position:absolute; width:780px; height:10px; padding:5px 10px; right:0; bottom:0; text-align:right;} 
#focus .btn span {display:inline-block; _display:inline; _zoom:1; width:25px; height:10px; _font-size:0; margin-left:5px; cursor:pointer; background:#fff;} 
#focus .btn span.on {background:#fff;} 
#focus .preNext {width:45px; height:100px; position:absolute; top:90px; background:url(img/sprite.png) no-repeat 0 0; cursor:pointer;} 
#focus .pre {left:0;} 
#focus .next {right:0; background-position:right top;} 
</style>

$(function() { 
var sWidth = $("#focus").width(); //获取焦点图的宽度（显示面积） 
var len = $("#focus ul li").length; //获取焦点图个数 
var index = 0; 
var picTimer; 
//以下代码添加数字按钮和按钮后的半透明条，还有上一页、下一页两个按钮 
var btn = "<p class=&#39;btnBg&#39;></p><p class=&#39;btn&#39;>"; 
for(var i=0; i < len; i++) { 
btn += "<span></span>"; 
} 
btn += "</p><p class=&#39;preNext pre&#39;></p><p class=&#39;preNext next&#39;></p>"; 
$("#focus").append(btn); 
$("#focus .btnBg").css("opacity",0.5); 
//为小按钮添加鼠标滑入事件，以显示相应的内容 
$("#focus .btn span").css("opacity",0.4).mouseenter(function() { 
index = $("#focus .btn span").index(this); 
showPics(index); 
}).eq(0).trigger("mouseenter"); 
//上一页、下一页按钮透明度处理 
$("#focus .preNext").css("opacity",0.2).hover(function() { 
$(this).stop(true,false).animate({"opacity":"0.5"},300); 
},function() { 
$(this).stop(true,false).animate({"opacity":"0.2"},300); 
}); 
//上一页按钮 
$("#focus .pre").click(function() { 
index -= 1; 
if(index == -1) {index = len - 1;} 
showPics(index); 
}); 
//下一页按钮 
$("#focus .next").click(function() { 
index += 1; 
if(index == len) {index = 0;} 
showPics(index); 
}); 
//本例为左右滚动，即所有li元素都是在同一排向左浮动，所以这里需要计算出外围ul元素的宽度 
$("#focus ul").css("width",sWidth * (len)); 
//鼠标滑上焦点图时停止自动播放，滑出时开始自动播放 
$("#focus").hover(function() { 
clearInterval(picTimer); 
},function() { 
picTimer = setInterval(function() { 
showPics(index); 
index++; 
if(index == len) {index = 0;} 
},4000); //此4000代表自动播放的间隔，单位：毫秒 
}).trigger("mouseleave"); 
//显示图片函数，根据接收的index值显示相应的内容 
function showPics(index) { //普通切换 
var nowLeft = -index*sWidth; //根据index值计算ul元素的left值 
$("#focus ul").stop(true,false).animate({"left":nowLeft},300); //通过animate()调整ul元素滚动到计算出的position 
//$("#focus .btn span").removeClass("on").eq(index).addClass("on"); //为当前的按钮切换到选中的效果 
$("#focus .btn span").stop(true,false).animate({"opacity":"0.4"},300).eq(index).stop(true,false).animate({"opacity":"1"},300); //为当前的按钮切换到选中的效果 
} 
});