var alertFram = document.createElement("DIV");
alertFram.id="alertFram";
alertFram.style.position = "absolute";
alertFram.style.left = "50%";
alertFram.style.top = "50%";
alertFram.style.marginLeft = "-225px" ;
alertFram.style.marginTop = -75+document.documentElement.scrollTop+"px";
alertFram.style.width = "450px";
alertFram.style.height = "150px";
alertFram.style.background = "#ccc";
alertFram.style.textAlign = "center";
alertFram.style.lineHeight = "150px";
alertFram.style.zIndex = "10001";

strHtml = "<ul style=\"list-style:none;margin:0px;padding:0px;width:100%\">\n";
strHtml += " <li style=\"background:#DD828D;text-align:left;padding-left:20px;font-size:14px;font-weight:bold;height:25px;line-height:25px;border:1px solid #F9CADE;\">[提示]</li>\n";
strHtml += " <li style=\"background:#fff;text-align:center;font-size:12px;height:120px;line-height:120px;border-left:1px solid #F9CADE;border-right:1px solid #F9CADE;\">"+txt+"</li>\n";
strHtml += " <li style=\"background:#FDEEF4;text-align:center;font-weight:bold;height:25px;line-height:25px; border:1px solid #F9CADE;\"><input type=\"button\" value=\" 确 定 \" id=\"do_OK\" onclick=\"doOk()\" /></li>\n";
strHtml += "</ul>\n";

alertFram.innerHTML = strHtml;
document.body.appendChild(alertFram);
document.body.appendChild(shield);
this.setOpacity = function(obj,opacity){
if(opacity>=1)opacity=opacity/100;
try{ obj.style.opacity=opacity; }catch(e){}
try{
if(obj.filters.length>0&&obj.filters("alpha")){
obj.filters("alpha").opacity=opacity*150;
}else{
obj.style.filter="alpha(opacity=\""+(opacity*150)+"\")";
}
}catch(e){}
}
var c = 0;
this.doAlpha = function(){
if (++c > 20){clearInterval(ad);return 0;}
setOpacity(shield,c);
}
var ad = setInterval("doAlpha()",1);
this.doOk = function(){
document.body.removeChild(alertFram);
document.body.removeChild(shield);
document.body.onselectstart = function(){return true;}
document.body.oncontextmenu = function(){return true;}
}
document.getElementById("do_OK").focus();
document.body.onselectstart = function(){return false;}
document.body.oncontextmenu = function(){return false;}
}
</script>

<input type="button" value="点击这里" onclick="sAlert('test弹窗效果');" />