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<br/> <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> <script language="JavaScript"> 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 titleheight=25 //提示窗口标题高度 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;//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 <br/> 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。