js 实现 遮罩层

var shadeBgObj ;
var shadeMsgObj ;
var shadeTitle ;
function closeShadeWindow(){
 document.body.removeChild(shadeBgObj);
 document.getElementById("msgDiv").removeChild(shadeTitle);
 document.body.removeChild(shadeMsgObj);
}
function openShadeWindow(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;

   shadeBgObj=document.createElement("div");
   shadeBgObj.setAttribute('id','bgDiv');
   shadeBgObj.style.position="absolute";
   shadeBgObj.style.top="0";
   shadeBgObj.style.background="#777";
   shadeBgObj.style.filter="progid:DXImageTransform.Microsoft.Alpha(style=3,opacity=25,finishOpacity=75";
   shadeBgObj.style.opacity="0.6";
   shadeBgObj.style.left="0";
   shadeBgObj.style.width=sWidth + "px";
   shadeBgObj.style.height=sHeight + "px";
   shadeBgObj.style.zIndex = "10000";
   document.body.appendChild(shadeBgObj);
  
   shadeMsgObj=document.createElement("div")
   shadeMsgObj.setAttribute("id","msgDiv");
   shadeMsgObj.setAttribute("align","center");
   shadeMsgObj.style.background="white";
   shadeMsgObj.style.border="1px solid " + bordercolor;
   shadeMsgObj.style.position = "absolute";
   shadeMsgObj.style.left = "50%";
   shadeMsgObj.style.top = "50%";
   shadeMsgObj.style.font="12px/1.6em Verdana, Geneva, Arial, Helvetica, sans-serif";
   shadeMsgObj.style.marginLeft = "-225px" ;
   shadeMsgObj.style.marginTop = -75+document.documentElement.scrollTop+"px";
   shadeMsgObj.style.width = msgw + "px";
   shadeMsgObj.style.height =msgh + "px";
   shadeMsgObj.style.textAlign = "center";
   shadeMsgObj.style.lineHeight ="25px";
   shadeMsgObj.style.zIndex = "10001";
 
   shadeTitle=document.createElement("h4");
   shadeTitle.setAttribute("id","msgTitle");
   shadeTitle.setAttribute("align","center");
   shadeTitle.style.margin="0";
   shadeTitle.style.padding="0px";
   shadeTitle.style.background=bordercolor;
   shadeTitle.style.filter="progid:DXImageTransform.Microsoft.Alpha(startX=20, startY=20, finishX=100, finishY=100,style=1,opacity=75,finishOpacity=100);";
   shadeTitle.style.opacity="0.75";
   shadeTitle.style.border="0px solid " + bordercolor;
   shadeTitle.style.height="0px";
   shadeTitle.style.font="0px Verdana, Geneva, Arial, Helvetica, sans-serif";
   shadeTitle.style.color="white";
   shadeTitle.style.cursor="pointer";
   shadeTitle.innerHTML="关闭";
   shadeTitle.onclick=function(){
  document.body.removeChild(shadeBgObj);
  document.getElementById("msgDiv").removeChild(shadeTitle);
  document.body.removeChild(shadeMsgObj);
    }
 document.body.appendChild(shadeMsgObj);
 document.getElementById("msgDiv").appendChild(shadeTitle);
 var txt=document.createElement("p");
 txt.style.margin="1em 0"
 txt.setAttribute("id","msgTxt");
 txt.innerHTML=str;
 document.getElementById("msgDiv").appendChild(txt);
}