js回到顶部

 <!DOCTYPE html>

 <html lang="en">

 <head>

 <meta charset="UTF-8">

 <meta name="viewport" content="width=device-width, initial-scale=1.0">

 <meta http-equiv="X-UA-Compatible" content="ie=edge">

 <title>回到顶部</title>

 <style>

    * { padding: 0; margin: 0; }

    #box {width: 100%;height: 2400px;margin: auto;border: 1px solid red;box-sizing: border-box;}

    #top {width: 60px;height: 50px;line-height: 50px;background-color: orange;color: #fff;font-size: 12px;text-align: center;position: fixed;

          right: 20px;bottom: 20px;text-decoration: none;display: none;

    }

 </style>

 </head>

 <body>

   <div id="box"></div>

   <a href="javascript:;" id="top">返回顶部</a>

 </body>

 <script>

  window.onload = function () {

   var oTop = document.getElementById('top')

   // 获取页面可视区的高度

   var clientHeight = document.documentElement.clientHeight

   var timer = null

   var isTop = true

   // 滚动条滚动时触发

   window.onscroll = function () {

   var osTop = document.documentElement.scrollTop || document.body.scrollTop

   if (osTop >= clientHeight) {

     oTop.style.display = 'block'

   } else {

     oTop.style.display = 'none'

   }

   if (!isTop) {

     clearInterval(timer)

   }

   isTop = false

 }

 oTop.onclick = function () {

   timer = setInterval(function () {

     // 获取滚动条距离顶部的高度

     var osTop = document.documentElement.scrollTop || document.body.scrollTop

     var ispeed = Math.floor(-osTop / 5)

     document.documentElement.scrollTop = document.body.scrollTop = osTop + ispeed

     isTop = true

     if (osTop === 0) {

        clearInterval(timer)

     }

   }, 30)

  }

 }

 </script>

 </html>
巴特西

js回到顶部

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