JavaScript 点击页面上的按纽，弹出层，背景变灰

<html xmlns="http://www.w3.org/1999/xhtml" > 
<head> 
<title>点击页面上的按纽，弹出一个层，背景变灰</title> 
<script type="text/javascript" src="js/newDiv.js"></script> 
<meta http-equiv= "Content-Type " content= "text/html; charset=gb2312 " /> 
</head> 
<body> 
<p >点击页面上的按纽，弹出一个层，背景变灰</p> 
<input type= "button" onclick= " sAlert( '测试效果  嗯！效果还不错！ '); " value="点击这里 " /> 
<input type="button" id="btn" value="test" /> 
</body> 
</html>

var sWidth,sHeight; 
sWidth=document.body.offsetWidth;//浏览器工作区域内页面宽度 
sHeight=screen.height;//屏幕高度（垂直分辨率）

//背景层（大小与窗口有效区域相同，即当弹出对话框时，背景显示为放射状透明灰色） 
var bgObj=document.createElement( "div ");//创建一个div对象（背景层） 
//定义div属性，即相当于 
//   
bgObj.setAttribute( 'id ', 'bgDiv '); 
bgObj.style.position="absolute"; 
bgObj.style.top= "0"; 
bgObj.style.background= "#777 "; 
bgObj.style.filter= "progid:DXImageTransform.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"; 
bgObj.style.zIndex = "10000"; 
document.body.appendChild(bgObj);//在body内添加该div对象

var msgObj=document.createElement( "div")//创建一个div对象（提示框层） 
//定义div属性，即相当于 
//  
msgObj.setAttribute( "id", "msgDiv"); 
msgObj.setAttribute( "align", "center"); 
msgObj.style.background= "white "; 
msgObj.style.border= "1px solid " ; 
msgObj.style.position = "absolute"; 
msgObj.style.left = "50%"; 
msgObj.style.top = "50%"; 
msgObj.style.font= "12px/1.6em Verdana, Geneva, Arial, Helvetica, sans-serif"; 
msgObj.style.marginLeft = "-225px" ; 
msgObj.style.marginTop = -75+document.documentElement.scrollTop+ "px"; 
msgObj.style.width = msgw + "px"; 
msgObj.style.height =msgh + "px"; 
msgObj.style.textAlign = "center"; 
msgObj.style.lineHeight = "25px"; 
msgObj.style.zIndex = "10001";

var title=document.createElement( "h4");//创建一个h4对象（提示框标题栏） 
//定义h4的属性，即相当于 
// <h4 id= "msgTitle " align= "right " style= "margin:0; padding:3px; background-color:#336699; filter:progid:DXImageTransform.Microsoft.Alpha(startX=20, startY=20, finishX=100, finishY=100,style=1,opacity=75,finishOpacity=100); opacity:0.75; border:1px solid #336699; height:18px; font:12px Verdana,Geneva,Arial,Helvetica,sans-serif; color:white; cursor:pointer; " onclick= " "> 关闭 </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" ; 
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=removeObj;

var button=document.createElement( "input");//创建一个input对象（提示框按钮） 
//定义input的属性，即相当于 
// <input type= "button " align= "center " style= "width:100px; align:center; margin-left:250px; margin-bottom:10px; " value= "关闭 "> 
button.setAttribute( "type", "button"); 
button.setAttribute( "value", "关闭"); 
button.style.width= "60px"; 
button.style.align= "center"; 
button.style.marginLeft= "250px"; 
button.style.marginBottom= "10px"; 
button.style.background=bordercolor; 
button.style.border= "1px solid"; 
button.style.color= "white"; 
button.onclick=removeObj;

function removeObj() 
{//点击标题栏触发的事件 
document.body.removeChild(bgObj);//删除背景层Div 
document.getElementById( "msgDiv").removeChild(title);//删除提示框的标题栏 
document.body.removeChild(msgObj);//删除提示框层 
} 
document.body.appendChild(msgObj);//在body内添加提示框div对象msgObj 
document.getElementById( "msgDiv").appendChild(title);//在提示框div中添加标题栏对象title

var txt=document.createElement( "p");//创建一个p对象（提示框提示信息） 
//定义p的属性，即相当于 
// <p style= "margin:1em 0; " id= "msgTxt "> 测试效果 </p> 
txt.style.margin= "1em 0" 
txt.setAttribute( "id ", "msgTxt"); 
txt.innerHTML=str;//来源于函数调用时的参数值 
document.getElementById( "msgDiv").appendChild(txt);//在提示框div中添加提示信息对象txt 
document.getElementById( "msgDiv").appendChild(button);//在提示框div中添加按钮对象button 
} 
</script>

[Ctrl+A 全选注:如需引入外部Js需刷新才能执行]
注意style.position和style.zIndex两属性。