(function(){ var scrollEle = clientEle = document.documentElement, toTopBtn = document.getElementById("toTop"), compatMode = document.compatMode, isChrome = window.navigator.userAgent.indexOf("Chrome") === -1 ? false : true; //不同渲染模式以及Chrome的预处理 if(compatMode === "BackCompat" || isChrome){ scrollEle = document.body; } if(compatMode === "BackCompat"){ clientEle = document.body; } //返回顶部按钮的点击响应（注册函数），时间间隔和高度缩减率可以调节 toTopBtn.onclick = function(){ var moveInterval = setInterval(moveScroll, 10); function moveScroll(){ setScrollTop(getScrollTop() / 1.2); if(getScrollTop() === 0){ clearInterval(moveInterval); } } } //滚动时判断是否显示返回顶部按钮（注册函数） window.onscroll = function(){ var display = toTopBtn.style.display; if(getScrollTop() > getClientHeight()){ if(display === "none" || display === ""){ toTopBtn.style.display = "block"; } }else{ if(display === "block" || display === ""){ toTopBtn.style.display = "none"; } } } //获取和设置scrollTop function getScrollTop(){ return scrollEle.scrollTop; } function setScrollTop(value){ scrollEle.scrollTop = value; } //获取当前网页的展示高度（第一屏高度），此处Chrome正常 function getClientHeight(){ return clientEle.clientHeight; } })();