本文实例讲述了javascript实现点击按钮弹出一个可关闭层窗口同时网页背景变灰的方法。分享给大家供大家参考。具体分析如下：
这里点击按钮后，弹出一个可关闭的层窗口，随之网页背景变灰，在QQ网站上经常会看到QQ登录的效果，就和这个很类似，代码段基于JavaScript，根据你的情况使用，有时候是用CSS完成的这种功能。
<html> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <title>弹出一个层，页面变灰</title> <script language="javascript"> function alertWin(title, msg, w, h){ var titleheight = "23px"; // 窗口标题高度 var bordercolor = "#336699"; // 提示窗口的边框颜色 var titlecolor = "#FFFFFF"; // 窗口标题颜色 var titlebgcolor = "#336699"; // 窗口标题背景色 var bgcolor = "#FFFFFF"; // 提示内容的背景色 var iWidth = document.documentElement.clientWidth; var iHeight = document.documentElement.clientHeight; var bgObj = document.createElement("div"); 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); var msgObj=document.createElement("div"); msgObj.style.cssText = "position:absolute;font:11px '宋体';top:"+(iHeight-h)/2+"px;left:"+(iWidth-w)/2+"px;width:"+w+"px;height:"+h+"px;text-align:center;border:1px solid "+bordercolor+";background-color:"+bgcolor+";padding:1px;line-height:22px;z-index:102;"; document.body.appendChild(msgObj); var table = document.createElement("table"); msgObj.appendChild(table); table.style.cssText = "margin:0px;border:0px;padding:0px;"; table.cellSpacing = 0; var tr = table.insertRow(-1); var titleBar = tr.insertCell(-1); titleBar.style.cssText = "width:100%;height:"+titleheight+"px;text-align:left;padding:3px;margin:0px;font:bold 13px '宋体';color:"+titlecolor+";border:1px solid " + bordercolor + ";cursor:move;background-color:" + titlebgcolor; titleBar.style.paddingLeft = "10px"; titleBar.innerHTML = title; var moveX = 0; var moveY = 0; var moveTop = 0; var moveLeft = 0; var moveable = false; var docMouseMoveEvent = document.onmousemove; var docMouseUpEvent = document.onmouseup; titleBar.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 + w < iWidth) && y > 0 && (y + h < 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; } }; } var closeBtn = tr.insertCell(-1); closeBtn.style.cssText = "cursor:pointer; padding:2px;background-color:" + titlebgcolor; closeBtn.innerHTML = "<span>×</span>"; closeBtn.onclick = function(){ document.body.removeChild(bgObj); document.body.removeChild(msgObj); } var msgBox = table.insertRow(-1).insertCell(-1); msgBox.style.cssText = "font:10pt '宋体';"; msgBox.colSpan = 2; msgBox.innerHTML = msg; // 获得Event对象，用于兼容IE和FireFox function getEvent() { return window.event || arguments.callee.caller.arguments[0]; } } </script> </head> <body> <input type="button" value="点这里" /> </body> </html>