总结代码如下 ：
function init(){
window.onscroll=function(e){
var s = "";
s += "网页可见区域宽："+ document.body.clientWidth;
s += "<br/>网页可见区域高："+ document.body.clientHeight;
s += "<br/>网页可见区域宽："+ document.body.offsetWidth +" (包括边线的宽)";
s += "<br/>网页可见区域高："+ document.body.offsetHeight +" (包括边线的高)";
s += "<br/>网页正文全文宽："+ document.body.scrollWidth;
s += "<br/>网页正文全文高："+ document.body.scrollHeight;
s += "<br/>网页被卷去的高："+ document.body.scrollTop;
s += "<br/>网页被卷去的左："+ document.body.scrollLeft;
s += "<br/>网页正文部分上："+ window.screenTop;
s += "<br/>网页正文部分左："+ window.screenLeft;
s += "<br/>屏幕分辨率的高："+ window.screen.height;
s += "<br/>屏幕分辨率的宽："+ window.screen.width;
s += "<br/>屏幕可用工作区高度："+ window.screen.availHeight;
s += "<br/>屏幕可用工作区宽度："+ window.screen.availWidth;
s += "<br/>目标坐标："+ document.getElementById("site2").offsetTop;
var objTop=document.getElementById("site2").offsetTop;
var sum=document.body.clientHeight+document.body.scrollTop;
if(sum>=objTop) alert("开始加载!");
document.getElementById("screen").innerHTML = s ;
}