html代碼

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

css代碼

* {margin: 0;padding: 0;}body {height: 3000px;}#box {width: 100px;height: 100px;background: red;position: absolute;right: 0;}

JS代碼

var oBox = document.getElementById("box");var timer = null;var iH = document.documentElement.clientHeight;oBox.style.top = iH / 2 - oBox.offsetHeight / 2 + "px";document.onscroll = function () {var iT = document.documentElement.scrollTop || document.body.scrollTop;var iTarget = Math.round(iH / 2) - Math.round(oBox.offsetHeight / 2) + iT;move(oBox, iTarget);};function move(obj, iTarget) {clearInterval(timer);timer = setInterval(function () {var speed = (iTarget - obj.offsetTop) / 8;speed = speed > 0 ? Math.ceil(speed) : Math.floor(speed);if (obj.offsetTop == iTarget) {clearInterval(timer);} else {obj.style.top = obj.offsetTop + speed + 'px';}}, 30)}

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