//scrollTop;var scrollTop = Math.max(document.documentElement.scrollTop, document.body.scrollTop);// 屏幕可视区高度var viewHeight = document.compatMod === ‘CSS1Compat‘ ? document.documentElement.clientHeight : document.body.clientHeight;// 文档高度var documentHeight = document.compatMod === ‘CSS1Compat‘ ? document.documentElement.scrollHeight: document.body.scrollHeight;