javascript 特效实现(2)——回到顶部效果

时间：2023-03-08 15:37:46
<!DOCTYPE html>

<html lang="en">

<head>

    <meta charset="UTF-8">

    <meta http-equiv="X-UA-Compatible" content="IE=Edge,chrome=1">

    <title>回到顶部效果（原生js）</title>

    <style type="text/css">

        body{

            margin: 0;

        }

        .bg{

            width: 1022px;

            margin: 0 auto;

        }

        .btn{

            display: none;

            width: 75px;

            height: 75px;

            background:url(../images/网页top小图标（返回顶部）/返回顶部-085.png) no-repeat left top;

            position: fixed;

            left: 50%;

            margin-left: 530px;

            bottom: 10px;

            text-indent: -9999px;

            outline: none;

        }

        .btn:hover{

            background-position: 0 -75px;

        }

    </style>

    <script>

    var timer=null;

    var isScroll=true;

    //1.2构造oScroll函数

    function oScroll(){

        var osTop=document.documentElement.scrollTop||document.body.scrollTop;//1.1滚动高度,兼容

        var oSpeed=Math.ceil(osTop/4);//滚动速度

        document.documentElement.scrollTop=document.body.scrollTop=osTop-oSpeed;

        if(osTop==0){//判断到达顶部,清理定时器

            clearInterval(timer);

        }

        isScroll=true;

    }

    window.onload=function() {

        var obtn=document.getElementById('btn');//获取按钮元素

        var clientHeight=document.documentElement.clientHeight||document.body.clientHeight;

        // 1.点击返回按钮事件

        btn.onclick=function(){//为按钮绑定点击事件

            timer=setInterval(oScroll,50);

        }

        window.onscroll=function() {

            var osTop=document.documentElement.scrollTop||document.body.scrollTop;//1.1滚动高度,兼容

            if (osTop>clientHeight) {

                btn.style.display="block";

            }else{

                btn.style.display="none";

            }

            if(!isScroll){

                clearInterval(timer);

            }

            isScroll=false;

        }

    }    

    </script>

</head>

<body>

    <div class="bg">

        <img src="../images/jz.jpg">

    </div>

    <a href="javascript:void(0);" title="返回顶部" id="btn" class="btn">返回顶部</a>

</body>

</html>

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