jquery实现返回基部案例效果

<!doctype html>
<html>
<head>
<meta charset="gb2312">
<title>webrx-title</title>
<script src="js/jquery-1.11.1.min.js"></script>
<style>
/*returnTop*/  
p#back-to-top{  
    position:fixed;  
    display:none;  
    bottom:100px;  
    right:80px;  
}  
p#back-to-top a{  
    text-align:center;  
    text-decoration:none;  
    color:#d1d1d1;  
    display:block;  
    width:64px;  
    /*使用CSS3中的transition属性给跳转链接中的文字加入渐变效果*/  
    -moz-transition:color 1s;  
    -webkit-transition:color 1s;  
    -o-transition:color 1s;  
}  
p#back-to-top a:hover{  
    color:#979797;  
}  
p#back-to-top a span{  
    background-image:url(top1.png);  
    border-radius:6px;  
    display:block;  
    height:64px;  
    width:56px;  
    margin-bottom:5px;  
    /*使用CSS3中的transition属性给<span>标签背景颜色加入渐变效果*/  
    -moz-transition:background 1s;  
    -webkit-transition:background 1s;  
    -o-transition:background 1s;  
}  
#back-to-top a:hover span{  
    background-image:url(top1.png);  
} 
</style>
<script>
$(document).ready(function(e) {
//当滚动栏的位置处于距顶部100像素下面时。跳转链接出现，否则消失  
        $(function () {  
            $(window).scroll(function(){  
                if ($(window).scrollTop()>100){  
                    $("#back-to-top").fadeIn(1500);  
                }  
                else  
                {  
                    $("#back-to-top").fadeOut(1500);  
                }  
            });  
  
            //当点击跳转链接后。回到页面顶部位置  
  
            $("#back-to-top").click(function(){  
                $('body,html').animate({scrollTop:0},1000);  
                return false;  
            });  
        });  
   
});
</script>
</head>

<body>
aaa<br>bb<br>aaa<br>bb<br>aaa<br>bb<br>aaa<br>bb<br>aaa<br>bb<br>aaa<br>bb<br>
aaa<br>bb<br>aaa<br>bb<br>aaa<br>bb<br>aaa<br>bb<br>aaa<br>bb<br>aaa<br>bb<br>
aaa<br>bb<br>aaa<br>bb<br>aaa<br>bb<br>aaa<br>bb<br>aaa<br>bb<br>aaa<br>bb<br>
aaa<br>bb<br>aaa<br>bb<br>aaa<br>bb<br>aaa<br>bb<br>aaa<br>bb<br>aaa<br>bb<br>
aaa<br>bb<br>aaa<br>bb<br>aaa<br>bb<br>aaa<br>bb<br>aaa<br>bb<br>aaa<br>bb<br>
aaa<br>bb<br>aaa<br>bb<br>aaa<br>bb<br>aaa<br>bb<br>aaa<br>bb<br>aaa<br>bb<br>
aaa<br>bb<br>aaa<br>bb<br>aaa<br>bb<br>aaa<br>bb<br>aaa<br>bb<br>aaa<br>bb<br>
aaa<br>bb<br>aaa<br>bb<br>aaa<br>bb<br>aaa<br>bb<br>aaa<br>bb<br>aaa<br>bb<br>
aaa<br>bb<br>aaa<br>bb<br>aaa<br>bb<br>aaa<br>bb<br>aaa<br>bb<br>aaa<br>bb<br>
aaa<br>bb<br>aaa<br>bb<br>aaa<br>bb<br>aaa<br>bb<br>aaa<br>bb<br>aaa<br>bb<br>
aaa<br>bb<br>aaa<br>bb<br>aaa<br>bb<br>aaa<br>bb<br>aaa<br>bb<br>aaa<br>bb<br>
<p id="back-to-top"><a href="#top"><span></span>返回顶部</a></p>  
</body>
</html>