Jquery 实现banner图滚动效果

 <div id="focus">
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                </ul>
            </div>

/*广告图片切换*/
$(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 = "<div class=‘btnBg‘></div><div class=‘btn‘>";
    for (var i = 0; i < len; i++) {
        btn += "<span></span>";
    }
    btn += "</div><div class=‘preNext pre‘></div><div class=‘preNext next‘></div>";
    $("#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
    }
});

/*广告图片切换*/
#focus{width:340px;height:256px;overflow:hidden;position:relative;z-index:1;}
#focus ul{height:400px;position:absolute;}
#focus ul li{float:left;width:340px;height:318px;overflow:hidden; position:relative; background:#fff; }
#focus ul li p{position:absolute; top:233px; left:10px; font-size:12px; color:#ffffff; z-index:99999}
#focus ul li div{position:absolute; overflow:hidden;}
#focus .btnBg{position:absolute;width:800px;height:30px;left:0;bottom:0;background:#000;}
#focus .btn{position:absolute;width:780px;height:10px;padding:10px 10px;*padding:10px 10px;right:0;bottom:0;text-align:right;}
#focus .btn span{display:inline-block;_display:inline;_zoom:1;width:10px;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(/content/images/sprite.png) no-repeat 0 0;cursor:pointer;}
#focus .pre{left:0;}
#focus .next{right:0;background-position:right top;}
#focus ul,li{list-style:none;}
#focus img{border:0;}
#focus ul li{float:left;width:340px;height:256px;overflow:hidden;position:relative;background:#fff;}