创建带遮罩层的提示框

function showmsg(t_errmess){
    	var sl = document.body.scrollLeft;
	var sh = document.body.scrollTop;
	var ow = document.body.offsetWidth;
	var oh = document.body.offsetHeight;
	try{
		//alert("sl:"+sl+",sh:"+sh+",ow:"+ow+",oh:"+oh);
		var errDiv=document.getElementById("lay_err123");
		if(errDiv==null || typeof(errDiv)=="undefined"){
			errDiv = document.createElement("div");
			errDiv.id="lay_err123";
			if(ow>350){
				errDiv.style.width="300px";
				errDiv.style.left= (sl+ow/2-100)+"px";
			}else{
				errDiv.style.width="80%";
				errDiv.style.left="8%";
			}
			errDiv.style.position = "absolute";
			errDiv.style.top=(sh+oh/4)+"px";
			errDiv.style.backgroundColor="#99ccff";
			errDiv.style.border="2px solid #3399ff";
			errDiv.style.zIndex=200;
			errDiv.style.textAlign="left";
			document.body.appendChild(errDiv);
		}
		
		var lay1 = document.getElementById("lay1_error");
		if(lay1==null || typeof(lay1)=="undefined"){
			lay1 = document.createElement("iframe");
			lay1.id="lay1_error";
			lay1.style.width = ow+"px";
			lay1.style.height = oh+"px";
			lay1.style.position = "absolute";
			lay1.style.left = sl+"px";
			lay1.style.top = sh+"px";
			lay1.style.backgroundColor="#99ccff";
			lay1.style.zIndex=1;
			lay1.style.filter = "alpha(opacity=50)";
			
			document.body.appendChild(lay1);
		}
		
		
		var str="<div style=\"float:right;clear:both;cursor:hand;color:red;width:30px;\" "
				+"onclick=\"document.getElementById('lay_err123').style.display='none';document.getElementById('lay1_error').style.display='none';\">[关闭]</div><br>";
		errDiv.innerHTML=str+t_errmess;
		errDiv.style.display="";
		lay1.style.display="";
		
	}catch(e){
		//alert(e.description);
	}

}