请大家帮个忙，谢谢！

Question

我写了一个函数，弹出一个iframe，
代码如下：
//判断当前页中是否有iframe
     var ParentObj=window;
     var parentLocation=window.parent.location;
     var nowLocation=window.location;
     var ParentIframe;
     
     while(parentLocation!=nowLocation)
     {
         ParentObj=ParentObj.window.parent;
         nowLocation=ParentObj.window.location;
         parentLocation=ParentObj.parent.location;
     }
     
     var aaa=ParentObj.document.createElement("iframe");
    
     aaa.src=WebString;
     // aaa.setAttribute("style",styleString);
    aaa.setAttribute("id",YourID);
   // aaa.id=YourID;
//    aaa.setAttribute("width","500px");
//    aaa.setAttribute("heigth","500px");
    ParentObj.window.document.body.appendChild(aaa);
    var bbbbbb=ParentObj.document.getElementById(YourID);
    bbbbbb.style.position="absolute"
    bbbbbb.style.zIndex="10000";
    
    alert(bbbbbb.id);    
    //得到包含的网页的高度和宽度
     var bHeight = bbbbbb.contentWindow.document.body.scrollHeight;
     var dHeight = bbbbbb.contentWindow.document.documentElement.scrollHeight;
     var bWidth=bbbbbb.contentWindow.document.body.scrollWidth;
     var dWidth=bbbbbb.contentWindow.document.documentElement.scrollWidth;
     var height = Math.max(bHeight, dHeight);
     var width=Math.max(bWidth,dWidth);
     
     //得到浏览器屏幕可见区域的高度和宽度
     var ScreenHeigth=window.top.document.body.offsetHeight;
     var ScreenWidth=window.top.document.body.offsetWidth;
    
     var top;
     var left;
     var bottom="60px";
     var right;
     
     if(width>ScreenWidth)
     {
         bbbbbb.style.width=ScreenWidth;
         left="0px";
         right="0px";
     }
     else
     {
         left=(ScreenWidth-width)/2+"px";
         right=left;
     }
     
     if(height>ScreenHeigth)
     {
       
         top=window.top.document.body.scrollTop+"px";
         bottom="0px";
     }
     else
     {
        top=(window.top.document.body.scrollTop+ScreenHeigth-height)/2+"px";
        bottom=top;
     }
     
     bbbbbb.style.top=top;
     bbbbbb.style.left=left;
     bbbbbb.style.height=Math.min(height,ScreenHeigth);
     bbbbbb.style.width=Math.min(width,ScreenWidth);    alert(window.top.document.body.clientHeight);
    alert(window.top.document.body.offsetHeight);
    
    var shadeHieght=window.top.document.body.scrollHeight;
    var shadeWidth=window.top.document.body.scrollWidth;
    window.top.document.body.appendChild(CreateShade("Name",shadeWidth,shadeHieght,1000));请注意红色字体部分，如果不加，那么var bHeight = bbbbbb.contentWindow.document.body.scrollHeight;
这句就会出现  Microsoft JScript 运行时错误: 缺少对象  错误。另外，如果把YourID变量用一个常量代替，则去掉红色字体部分也能正确运行。请大家帮忙看看是怎么回事？谢谢。我都弄了一天了。分不多，请大家包涵！

Answer 1

function PopupContent(WebString)
{
 //判断当前页中是否有iframe
     var ParentObj=window;
     var parentLocation=window.parent.location;
     var nowLocation=window.location;
     var ParentIframe;
     
     while(parentLocation!=nowLocation)
     {
         ParentObj=ParentObj.window.parent;
         nowLocation=ParentObj.window.location;
         parentLocation=ParentObj.parent.location;
     }
     
     var aaa=ParentObj.document.createElement("iframe");
    
     aaa.src=WebString;
    aaa.setAttribute("id","aaaaaa");    ParentObj.window.document.body.appendChild(aaa);
    var bbbbbb=ParentObj.document.getElementById("aaaaaa");
    bbbbbb.style.position="absolute"
    bbbbbb.style.zIndex="10000";
 
    alert(bbbbbb.id);    
    //得到包含的网页的高度和宽度
     var bHeight = bbbbbb.contentWindow.document.body.scrollHeight;
     var dHeight = bbbbbb.contentWindow.document.documentElement.scrollHeight;
     var bWidth=bbbbbb.contentWindow.document.body.scrollWidth;
     var dWidth=bbbbbb.contentWindow.document.documentElement.scrollWidth;
     var height = Math.max(bHeight, dHeight);
     var width=Math.max(bWidth,dWidth);
     
     //得到浏览器屏幕可见区域的高度和宽度
     var ScreenHeigth=window.top.document.body.offsetHeight;
     var ScreenWidth=window.top.document.body.offsetWidth;
    
     var top;
     var left;
     var bottom="60px";
     var right;
     
     if(width>ScreenWidth)
     {
         bbbbbb.style.width=ScreenWidth;
         left="0px";
         right="0px";
     }
     else
     {
         left=(ScreenWidth-width)/2+"px";
         right=left;
     }
     
     if(height>ScreenHeigth)
     {
       
         top=window.top.document.body.scrollTop+"px";
         bottom="0px";
     }
     else
     {
        top=(window.top.document.body.scrollTop+ScreenHeigth-height)/2+"px";
        bottom=top;
     }
     
     bbbbbb.style.top=top;
     bbbbbb.style.left=left;
     bbbbbb.style.height=Math.min(height,ScreenHeigth);
     bbbbbb.style.width=Math.min(width,ScreenWidth);    alert(window.top.document.body.clientHeight);
    alert(window.top.document.body.offsetHeight);
    
    var shadeHieght=window.top.document.body.scrollHeight;
    var shadeWidth=window.top.document.body.scrollWidth;
    window.top.document.body.appendChild(CreateShade("Name",shadeWidth,shadeHieght,1000));
}朋友们可以运行一下，看看把红色字体部分去掉以后还能正常运行吗

Answer 2

只有你自己回答，分就给您了！谢谢您！找着原因了，是因为如果没有那个alert的话，接着就这行下一句了，此时iframe还没加载完毕，当然找不到cotentDocument对象了！
解决方法：
  if(aaa.attachEvent)
     {
         aaa.attachEvent("onload",function(){shia()});
     }
     else
     {
         aaa.onload=function(){
         alert("第二个加载完成");
shia();
         }
     }在onload事件中再调用哪些方法，完整代码，自己随便写的，可能有点乱。function PopupContent(WebString)
{
 //判断当前页中是否有iframe
     var ParentObj=window;
     var parentLocation=window.parent.location;
     var nowLocation=window.location;
     var ParentIframe;
     
     while(parentLocation!=nowLocation)
     {
         ParentObj=ParentObj.window.parent;
         nowLocation=ParentObj.window.location;
         parentLocation=ParentObj.parent.location;
     }
     
     var aaa=ParentObj.document.createElement("iframe");
    
     aaa.src=WebString;
     aaa.setAttribute("id","aaaaaa");
        ParentObj.window.document.body.appendChild(aaa);
        
     if(aaa.attachEvent)
     {
         aaa.attachEvent("onload",function(){shia()});
     }
     else
     {
         aaa.onload=function(){
         alert("第二个加载完成");
shia();
         }
     }
function shia()
{
     var bbbbbb=window.top.document.getElementById("aaaaaa");
    bbbbbb.style.position="absolute"
    bbbbbb.style.zIndex="10000";
     //得到包含的网页的高度和宽度
     var bHeight = bbbbbb.contentWindow.document.body.scrollHeight;
     var dHeight = bbbbbb.contentWindow.document.documentElement.scrollHeight;
     var bWidth=bbbbbb.contentWindow.document.body.scrollWidth;
     var dWidth=bbbbbb.contentWindow.document.documentElement.scrollWidth;
     var height = Math.max(bHeight, dHeight);
     var width=Math.max(bWidth,dWidth);
     
     //得到浏览器屏幕可见区域的高度和宽度
     var ScreenHeigth=window.top.document.body.offsetHeight;
     var ScreenWidth=window.top.document.body.offsetWidth;
    
     var top;
     var left;
     var bottom="60px";
     var right;
     
     if(width>ScreenWidth)
     {
         bbbbbb.style.width=ScreenWidth;
         left="0px";
         right="0px";
     }
     else
     {
         left=(ScreenWidth-width)/2+"px";
         right=left;
     }
     
     if(height>ScreenHeigth)
     {
       
         top=window.top.document.body.scrollTop+"px";
         bottom="0px";
     }
     else
     {
        top=(window.top.document.body.scrollTop+ScreenHeigth-height)/2+"px";
        bottom=top;
     }
     
     bbbbbb.style.top=top;
     bbbbbb.style.left=left;
     bbbbbb.style.height=Math.min(height,ScreenHeigth);
     bbbbbb.style.width=Math.min(width,ScreenWidth);
    
    var shadeHieght=window.top.document.body.scrollHeight;
    var shadeWidth=window.top.document.body.scrollWidth;
    window.top.document.body.appendChild(CreateShade("Name",shadeWidth,shadeHieght,1000));}