基于JavaScript实现回到页面顶部动画代码

//页面加载后触发window.onload = function(){var btn = document.getElementById('btn');var timer = null;var isTop = true;//获取页面可视区高度var clientHeight = document.documentElement.clientHeight;//滚动条滚动时触发window.onscroll = function() {//显示回到顶部按钮var osTop = document.documentElement.scrollTop || document.body.scrollTop;if (osTop >= clientHeight) {btn.style.display = "block";} else {btn.style.display = "none";};//回到顶部过程中用户滚动滚动条，停止定时器if (!isTop) {clearInterval(timer);};isTop = false;};btn.onclick = function() {//设置定时器timer = setInterval(function(){//获取滚动条距离顶部高度var osTop = document.documentElement.scrollTop || document.body.scrollTop;var ispeed = Math.floor(-osTop / 7);document.documentElement.scrollTop = document.body.scrollTop = osTop+ispeed;//到达顶部，清除定时器if (osTop == 0) {clearInterval(timer);};isTop = true;},30);};};