JavaScript 弹出层效果

function sAlert(str){
   var msgw,msgh,bordercolor;
   msgw=400;//提示窗口的宽度
   msgh=100;//提示窗口的高度
   titleheight=25 //提示窗口标题高度
   bordercolor="#336699";//提示窗口的边框颜色
   titlecolor="#99CCFF";//提示窗口的标题颜色
 
   var sWidth,sHeight;
   sWidth=document.body.offsetWidth;
   sHeight=screen.height;
   var bgObj=document.createElement("div");
   bgObj.setAttribute('id','bgDiv');
   bgObj.style.position="absolute";
   bgObj.style.top="0";
   bgObj.style.background="#777";
   bgObj.style.filter="progid:DXImageTransform.Microsoft.Alpha(style=3,opacity=25,finishOpacity=75";
   bgObj.style.opacity="0.6";
   bgObj.style.left="0";
   bgObj.style.width=sWidth + "px";
   bgObj.style.height=sHeight + "px";
   bgObj.style.zIndex = "10000";
   document.body.appendChild(bgObj);
   
   var msgObj=document.createElement("div")
   msgObj.setAttribute("id","msgDiv");
   msgObj.setAttribute("align","center");
   msgObj.style.background="white";
   msgObj.style.border="1px solid " + bordercolor;
   msgObj.style.position = "absolute";
   msgObj.style.left = "50%";
   msgObj.style.top = "50%";
   msgObj.style.font="12px/1.6em Verdana, Geneva, Arial, Helvetica, sans-serif";
   msgObj.style.marginLeft = "-225px" ;
   msgObj.style.marginTop = -75+document.documentElement.scrollTop+"px";
   msgObj.style.width = msgw + "px";
   msgObj.style.height =msgh + "px";
   msgObj.style.textAlign = "center";
   msgObj.style.lineHeight ="25px";
   msgObj.style.zIndex = "10001";
   
   var title=document.createElement("h4");
   title.setAttribute("id","msgTitle");
   title.setAttribute("align","right");
   title.style.margin="0";
   title.style.padding="3px";
   title.style.background=bordercolor;
   title.style.filter="progid:DXImageTransform.Microsoft.Alpha(startX=20, startY=20, finishX=100, finishY=100,style=1,opacity=75,finishOpacity=100);";
   title.style.opacity="0.75";
   title.style.border="1px solid " + bordercolor;
   title.style.height="18px";
   title.style.font="12px Verdana, Geneva, Arial, Helvetica, sans-serif";
   title.style.color="white";
   title.style.cursor="pointer";
   title.innerHTML="关闭";
   title.onclick=function(){
          document.body.removeChild(bgObj);
          document.getElementById("msgDiv").removeChild(title);
          document.body.removeChild(msgObj);
        }
   document.body.appendChild(msgObj);
   document.getElementById("msgDiv").appendChild(title);
   var txt=document.createElement("p");
   txt.style.margin="1em 0"
   txt.setAttribute("id","msgTxt");
   txt.innerHTML=str;
   document.getElementById("msgDiv").appendChild(txt);
}