<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>无标题文档</title>
<script language="javascript">
function alertWin(str){ 
 var msgw, msgh, bordercolor;
 msgw = 300;//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 = "#A480B2";//提示窗口的边框颜色
 titlecolor = "#A480B2";//提示窗口的标题颜色
  
 //根据自己需求注意宽度和高度的调整
 var iWidth = document.documentElement.clientWidth; 
 var iHeight = document.documentElement.clientHeight; 
 //遮罩层
 var bgObj = document.createElement("div"); 
 bgObj.setAttribute("id", "bgObj");//设置ID
 bgObj.style.cssText = "position:absolute;left:0px;top:0px;width:"+iWidth+"px;height:"+Math.max(document.body.clientHeight, iHeight)+"px;filter:Alpha(Opacity=30);opacity:0.3;background-color:#000000;z-index:101;";
 document.body.appendChild(bgObj);

 //弹出窗口
 var msgObj=document.createElement("div");
 msgObj.setAttribute("id", "msgDiv");//可以用bgObj.id="msgDiv"的方法,是为div指定属性值
 msgObj.setAttribute("align", "center");//为div的align赋值
 msgObj.style.background = "white";//背景颜色为白色
 msgObj.style.border = "1px solid " + bordercolor;//边框属性,颜色在上面已经赋值
 msgObj.style.position = "absolute";//绝对定位
 msgObj.style.left = (iWidth-msgw)/2  ;//从左侧开始位置
 msgObj.style.top = (iHeight-msgh)/2;//从上部开始位置
 msgObj.style.font = "12px/1.6em Verdana, Geneva, Arial, Helvetica, sans-serif";//字体属性
 msgObj.style.width = msgw + "px";//提示框的宽(上面定义过)
 msgObj.style.height = msgh + "px";//提示框的高(上面定义过)
 msgObj.style.textAlign = "center";//文本位置属性,居中。
 msgObj.style.lineHeight = "25px";//行间距
 msgObj.style.zIndex = "102";//层的z轴位置
 document.body.appendChild(msgObj);

 //弹出窗口标题
 var title = document.createElement("div");//创建一个标题对象
 title.setAttribute("id", "msgTitle");//为标题对象填加id
 title.style.margin = "0";//浮动
 title.style.padding = "3px";//浮动
 title.style.background = titlecolor;//背景颜色
 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";//透明
 //title.style.border="1px solid " + bordercolor;//边框
 title.style.height = "25px";//高度
 title.style.font = "12px Verdana, Geneva, Arial, Helvetica, sans-serif";//字体属性
 //title.style.color = "red";//文字颜色
 title.style.cursor = "move";//鼠标样式
 title.innerHTML="<table border='0' width='100%'><tr><td align='left'>系统信息</td><td align=\"right\"><a href='#' onclick='closeDiv()'>关闭</a></td></tr></table>";

 //设置窗口可移动

 var moveX = 0;
 var moveY = 0;
 var moveTop = 0;
 var moveLeft = 0;
 var moveable = false;
 var docMouseMoveEvent = document.onmousemove;
 var docMouseUpEvent = document.onmouseup;
 title.onmousedown = function() {
   var evt = getEvent();
   moveable = true; 
   moveX = evt.clientX;
   moveY = evt.clientY;
   moveTop = parseInt(msgObj.style.top);
   moveLeft = parseInt(msgObj.style.left);   
   document.onmousemove = function() {   
         if (moveable){
     var evt = getEvent();
     var x = moveLeft + evt.clientX - moveX;
     var y = moveTop + evt.clientY - moveY;
     if ( x > 0 &&( x + msgw < iWidth) && y > 0 && (y + msgh < iHeight) ){
      msgObj.style.left = x + "px";
      msgObj.style.top = y + "px";
     }
    } 
   };
   document.onmouseup = function (){ 
    if (moveable) { 
     document.onmousemove = docMouseMoveEvent;
     document.onmouseup = docMouseUpEvent;
     moveable = false; 
     moveX = 0;
     moveY = 0;
     moveTop = 0;
     moveLeft = 0;
    } 
   };
  }
 //获得事件Event对象,用于兼容IE和FireFox
 function getEvent() {
  return window.event || arguments.callee.caller.arguments[0];
 }
 
 msgObj.appendChild(title);//在提示框中增加标题
 var txt = document.createElement("p");
 txt.style.margin = "1em 0";//文本浮动
 txt.setAttribute("id", "msgTxt");//为p属性增加id属性
 txt.innerHTML = str;//把传进来的值赋给p属性
 msgObj.appendChild(txt);//把p属性增加到提示框里
}

//添加关闭功能
function closeDiv() {
    var msgTitelObject = document.getElementById("msgDiv");
    document.body.removeChild(msgTitelObject);
    var bgObj = document.getElementById("bgObj");
    document.body.removeChild(bgObj);

}

</script>
</head>
<body>
<input type="button" value="点这里" onclick="alertWin('消息主题');" />
</body>
</html>