jQuery 图片轮播的代码分离

<div id="scrollPics">
    <ul class="slider" >
        <li><img src="images/ads/1.gif"/></li>
        <li><img src="images/ads/2.gif"/></li>
        <li><img src="images/ads/3.gif"/></li>
        <li><img src="images/ads/4.gif"/></li>
        <li><img src="images/ads/5.gif"/></li>
    </ul>
    <ul class="num" >
        <li class="on">1</li>
        <li>2</li>
        <li>3</li>
        <li>4</li>
        <li>5</li>
    </ul>
</div>

#scrollPics{
    height: 150px;
    width: 100%;
    margin-bottom: 10px;
    overflow: hidden;
    position:relative;
}
.num{
    position:absolute;
    right:5px;
    bottom:5px;
}
#scrollPics .num li{
    float: left;
    color: #FF7300;
    text-align: center;
    line-height: 16px;
    width: 16px;
    height: 16px;
    cursor: pointer;
    overflow: hidden;
    margin: 3px 1px;
    border: 1px solid #FF7300;
    background-color: #fff;
}
#scrollPics .num li.on{
    color: #fff;
    line-height: 21px;
    width: 21px;
    height: 21px;
    font-size: 16px;
    margin: 0 1px;
    border: 0;
    background-color: #FF7300;
    font-weight: bold;
}

//滚动广告
    var len = $(".num > li").length;
    var index = 0;  //图片序号
    var adTimer;
    $(".num li").mouseover(function() {
        index = $(".num li").index(this);  //获取鼠标悬浮 li 的index
        showImg(index);
    }).eq(0).mouseover();
    //滑入停止动画，滑出开始动画.
    $('#scrollPics').hover(function() {
        clearInterval(adTimer);
    }, function() {
        adTimer = setInterval(function() {
            showImg(index)
            index++;
            if (index == len) {       //最后一张图片之后，转到第一张
                index = 0;
            }
        }, 3000);
    }).trigger("mouseleave");

    function showImg(index) {
        var adHeight = $("#scrollPics>ul>li:first").height();
        $(".slider").stop(true, false).animate({
            "marginTop": -adHeight * index + "px"    //改变 marginTop 属性的值达到轮播的效果
        }, 1000);
        $(".num li").removeClass("on")
            .eq(index).addClass("on");
    }