麻烦各位帮我看下 js

     var baidu=baidu||{version:"1-1-0"};
     var baidu.page=baidu.page||{};
     var D=baidu.page;
     var M=D.getWidth()||500;
     var E=D.getHeight()||500;
    var A=document.createElement("iframe");
     A.id="shadowIframe";
     A.style.filter="alpha(opacity=0)";
     A.style.opacity="0";
     A.style.position="absolute";
     A.className="VirtualScreen"
     A.style.width=(M-20)+"px";
     A.style.height=(E-20)+"px";
     A.style.display="block"
    document.body.insertBefore(A,document.body.firstChild);
            
            baidu.page.getHeight=function(){var f=document,a=f.body,d=f.documentElement,c= Math.max(d.scrollHeight,a.scrollHeight,c.clientHeight)};
            baidu.page.getWidth=function(){var f=document,a=f.body,d=f.documentElement,c= Math.max(d.scrollWidth,a.scrollWidth,c.clientWidth)};

其中这句的意义,和作用.
     var baidu=baidu||{version:"1-1-0"};
     var baidu.page=baidu.page||{};
     var D=baidu.page;
且为什么不能运行.