可拖动的弹出层提示效果

<script language=javascript>
var cao_x,cao_y;

function cao888()
{
this.display=display;
}

function display()
{
document.write("<table align=center><tr><td><button style='width:100px;height:30px;font-size:12px;border:1px solid #A4B3C8;background-color:green;' type=button onclick=document.getElementById('cao1').style.display='block' onfocus=this.blur()>点击弹出</button></td></tr></table>");
document.write("<div id='cao1' style='font-size:12px;position:absolute;display:none;text-align:center;overflow:visible'>");
document.write("<div style='position:absolute;top:expression((body.clientHeight-300)/2);left:expression((body.clientWidth-200)/2);width:200px;height:180px;background-color:#dbdbdb;border:1px solid #cccccc;'>");
document.write("<table width=200 height=20 bgcolor=green onmousedown='cao_x=event.x-parentNode.style.pixelLeft;cao_y=event.y-parentNode.style.pixelTop;setCapture();' onmouseup='releaseCapture();' onmousemove='caoMove(this.parentNode)' style='cursor:move;'>");
document.write("<tr align=center>");
document.write("<td align=left>可拖动的弹出提示效果</td>");
document.write("</tr>");
document.write("</table>");
document.write("<br><br>酷站(sincol)<br>http://www.sincol.net/<br><br><span style= cursor:hand onclick=this.parentNode.parentNode.style.display='none';>关闭</span>");
document.write(" </div>");
document.write("</div>");
}
function caoMove(obj) //实现层的拖移
{
if(event.button==1)
{
var caoX=obj.clientLeft;
var caoY=obj.clientTop;
obj.style.pixelLeft=caoX+(event.x-cao_x);
obj.style.pixelTop=caoY+(event.y-cao_y);
}
}
</script><script language=javascript>
var mycao=new cao888();
mycao.display();
</script>