html/index8.html at master · wodesj33/html · GitHub

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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en">

<head>
    <title>Javascript 回到顶部效果</title>
    <!-- <link rel="stylesheet" type="text/css" href="style.css" /> -->
    <style>
#btn {
    width:40px;
    height:40px;
   position:absolute;   /* //固定定位设置 */
    left:50%;
    margin-left:610px;
    bottom:30px;
    background:url(http://img.mukewang.com/535e0dc100010e9c00400080.jpg) no-repeat left top;
    display:none;
    position:fixed;
    }
#btn:hover {
    background:url(http://img.mukewang.com/535e0dc100010e9c00400080.jpg) no-repeat 0 -39px;
    }
.box {
    width:1190px;
    /*  //实现大图居中 */
    margin:0 auto;
    }
    </style>
</head>

<body>

    <div class="box">
        <img src="http://img.mukewang.com/535e0ce800015b7511902787.jpg" />
    </div>
    <a href="javascript:;" id="btn" title="回到顶部"></a>
    <script src="http://libs.baidu.com/jquery/1.9.0/jquery.js" type="text/javascript"></script>
    <script>
        $(function () {
            $(window).scroll(function () {
                var h = $(window).height();
                var scrolls = $(this).scrollTop();
                var lazyheight = parseFloat(h) + parseFloat(scrolls);
                if (lazyheight - 200 > h) {
                    $("#btn").show();
                } else {
                    $("#btn").hide();
                }
            })

            $("#btn").click(function () {
                $('body,html').animate({
                    scrollTop: 0
                }, 500);
            })
        })
    </script>
</body>

</html>