JS缓冲运动案例：右侧居中悬浮窗

<!DOCTYPE html>
<html lang="zh-CN">
<head>
  <meta charset="UTF-8">
  <title>JS小案例：右侧缓冲悬浮框</title>
  <style>
    body {
      height: 2000px;
      margin: 0px;
    }
    #div1 {
      width: 100px;
      height: 150px;
      background: red;
      position: absolute;
      right: 0;
      bottom:calc(50% - 75px);
    }
  </style>
  <script>
    window.onscroll = function () {
      startMove();
    }
    var timer = null;
    function startMove() {
      var oDiv = document.getElementById('div1');
      clearInterval(timer);
      timer = setInterval(function () {
        var scrollTop = document.documentElement.scrollTop || document.body.scrollTop;
        var iTarget = (document.documentElement.clientHeight - oDiv.offsetHeight) / 2 + scrollTop;
        iTarget = Math.ceil(iTarget);
        var speed = (iTarget - oDiv.offsetTop) / 4;
        speed = speed > 0 ? Math.ceil(speed) : Math.floor(speed);
        if (oDiv.offsetTop == iTarget) {
          clearInterval(timer);
        } else {
          oDiv.style.top = oDiv.offsetTop + speed + 'px';
        }
      }, 30)
    }
  </script>
</head>
<body>
  <div id='div1'></div>
</body>
</html>
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