document.compatMode

在我电脑屏幕上显示的 电脑是 1920*1080这是在document.compatMode:css1Compat模式

window.screen.availWidth
1920
window.screen.availWidth
1920
window.screen.availHeight
1057
window.screen.width
1920
window.screen.height
1080
window.document.body.offsetHeight
4901
window.document.body.clientWidth
1305
document.body.clientHeight
4901
document.body.clientWidth
1305
document.documentElement.clientHeight
460
document.documentElement.clientWidth
1305

现在是document.compatMode:BackCompat：页面没有!doctype声明

document.body.clientHeight
460
document.body.clientWidth
1320
document.documentElement.clientHeight
460
document.documentElement.clientWidth
1320

以上红色部分就是说document.compatMode模式的区别下的网页可视区域的宽和高

so:

var height=document.compatMode='css1Compat':document.documentElement.clientHeight ? document.body.clientHeight;

if (document.compatMode == "BackCompat") {
cWidth = document.body.clientWidth;
cHeight = document.body.clientHeight;
sWidth = document.body.scrollWidth;
sHeight = document.body.scrollHeight;
sLeft = document.body.scrollLeft;
sTop = document.body.scrollTop;
}
else { //document.compatMode == "CSS1Compat"
cWidth = document.documentElement.clientWidth;
cHeight = document.documentElement.clientHeight;
sWidth = document.documentElement.scrollWidth;
sHeight = document.documentElement.scrollHeight;
sLeft = document.documentElement.scrollLeft == 0 ? document.body.scrollLeft : document.documentElement.scrollLeft;
sTop = document.documentElement.scrollTop == 0 ? document.body.scrollTop : document.documentElement.scrollTop;
}