今天在经典看到有人把这效果独立出来了
http://bbs.blueidea.com/thread-2688074-1-1.html
如同Lightbox的效果那边，或者说和Windows关闭系统前的那一刻类似，为突出显示主题而采取的暗淡背景的方法在Web2.0的站点风格中被越来越多的使用。
(关于Lightbox：http://www.cnbruce.com/blog/showlog.asp?cat_id=34&log_id=1005 )
现在，当弹出千篇一律的Alert警告框被这样的一种方式取代时，给人的感觉是相当的新鲜的。
这样
<input type="button" value="点击这里" onclick="sAlert('测试效果<br>还可以直接书写HTML代码 <br>© 2006');" />
<script type="text/javascript" language="javascript">
//Author:Daviv
//Blog:http://blog.163.com/jxdawei
//Date:2006-10-28
//Email:jxdawei@gmail.com
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
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=document.body.offsetHeight;
var bgObj=document.createElement("div");
bgObj.setAttribute('id','bgDiv');
bgObj.style.position="absolute";
bgObj.style.top="0";
bgObj.style.background="#777";
bgObj.style.filter="progidXImageTransform.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";
document.body.appendChild(bgObj);
var msgObj=document.createElement("div")
msgObj.setAttribute("id","msgDiv");
msgObj.setAttribute("align","center");
msgObj.style.position="absolute";
msgObj.style.background="white";
msgObj.style.font="12px/1.6em Verdana, Geneva, Arial, Helvetica, sans-serif";
msgObj.style.border="1px solid " + bordercolor;
msgObj.style.width=msgw + "px";
msgObj.style.height=msgh + "px";
msgObj.style.top=(document.documentElement.scrollTop + (sHeight-msgh)/2) + "px";
msgObj.style.left=(sWidth-msgw)/2 + "px";
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;
doc
把SCRIPT做成一个JS文件就可以了