js中关于可视区、实际区域一些知识的个人理解

var clientW = document.documentElement.clientWidth || document.body.clientWidth;

var clientH = document.documentElement.clientHeight || document.body.clientHeight;

var offsetW = document.documentElement.scrollWidth || document.body.scrollWidth;

var offsetH = document.documentElement.scrollHeight || document.body.scrollHeight;

        

var bodyW = (offsetW>clientW)?offsetW:clientW;

var bodyH = (offsetH>clientH)?offsetH:clientH;