这一段代码啥意思？？

var showad = true;

var Toppx = 60;

var AdDivW = 200;

var AdDivH = 300;

var PageWidth = 800;

var MinScreenW = 1024;

var ClosebuttonHtml = '<div align="right" style="position:absolute; top:0px; right:0px; margin:2px; padding:2px;z-index:2000;"><a href="javascript:;" onclick="hidead()" style="color:red;text-decoration:none;font-size:12px;">关闭</a></div>'

var AdContentHtml = '<div align="center" style="color:green;font-size:23px;font-family:黑体;"> <a href="http://baike.baidu.com/item/悲伤逆流成河/20797534?fr=aladdin/" target="_blank"><img src="bsnlch.jpg" width="200" height="300" border="0"></a></div>';

document.write ('<div id="Javascript.LeftDiv" style="position: absolute;border: 1px solid #336699;background-color:#EEEEE2;z-index:1000;width:'+AdDivW+'px;height:'+AdDivH+'px;top:-1000px;word-break:break-all;display:none;">'+ClosebuttonHtml+'<div>'+AdContentHtml+'</div></div>');

document.write ('<div id="Javascript.RightDiv" style="position: absolute;border: 1px solid #336699;background-color:#EEEEE2;z-index:1000;width:'+AdDivW+'px;height:'+AdDivH+'px;top:-1000px;word-break:break-all;display:none;">'+ClosebuttonHtml+'<div>'+AdContentHtml+'</div></div>');

function scall(){

if(!showad){return;}

if (window.screen.width<MinScreenW){

alert("临时提示：\n\n显示器分辨率宽度小于"+MinScreenW+",不显示广告");

showad = false;

document.getElementById("Javascript.LeftDiv").style.display="none";

document.getElementById("Javascript.RightDiv").style.display="none";

return;

}