先给大家来张效果图，点击左上角的登录就会弹出登录系统：
下面跟大家分享下代码，代码复制到HTML文件里面能直接看到效果。
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312" />
<title></title>
<STYLE>
#login{
position: relative;
display: none;
top: 20px;
left: 30px;
background-color: #ffffff;
text-align: center;
border: solid 1px;
padding: 10px;
z-index: 1;
}
</STYLE>
<script type="text/javascript">
var W = screen.width;//取得屏幕分辨率宽度
var H = screen.height;//取得屏幕分辨率高度
function M(id){
return document.getElementById(id);//用M()方法代替document.getElementById(id)
}
function MC(t){
return document.createElement(t);//用MC()方法代替document.createElement(t)
};
//判断浏览器是否为IE
function isIE(){
return (document.all && window.ActiveXObject && !window.opera) ? true : false;
}
//取得页面的高宽
function getBodySize(){
var bodySize = [];
with(document.documentElement) {
bodySize[0] = (scrollWidth>clientWidth)?scrollWidth:clientWidth;//如果滚动条的宽度大于页面的宽度，取得滚动条的宽度，否则取页面宽度
bodySize[1] = (scrollHeight>clientHeight)?scrollHeight:clientHeight;//如果滚动条的高度大于页面的高度，取得滚动条的高度，否则取高度
}
return bodySize;
}
//创建遮盖层
function popCoverDiv(){
if (M("cover_div")) {
//如果存在遮盖层，则让其显示
M("cover_div").style.display = ‘block‘;
} else {
//否则创建遮盖层
var coverDiv = MC(‘div‘);
document.body.appendChild(coverDiv);
coverDiv.id = ‘cover_div‘;
with(coverDiv.style) {
position = ‘absolute‘;
background = ‘#CCCCCC‘;
left = ‘0px‘;
top = ‘0px‘;
var bodySize = getBodySize();
width = bodySize[0] + ‘px‘
height = bodySize[1] + ‘px‘;
zIndex = 0;
if (isIE()) {
filter = "Alpha(Opacity=60)";//IE逆境
} else {
opacity = 0.6;
}
}
}
}
//让登陆层显示为块
function showLogin()
{
var login=M("login");
login.style.display = "block";
}
//设置DIV层的样式
function change(){
var login = M("login");
login.style.position = "absolute";
login.style.border = "1px solid #CCCCCC";
login.style.background ="#F6F6F6";
var i=0;
var bodySize = getBodySize();
login.style.left = (bodySize[0]-i*i*4)/2+"px";
login.style.top = (bodySize[1]/2-100-i*i)+"px";
login.style.width = i*i*4 + "px";
login.style.height = i*i*1.5 + "px";
popChange(i);
}
//让DIV层大小循环增大
function popChange(i){
var login = M("login");
var bodySize = getBodySize();
login.style.left = (bodySize[0]-i*i*4)/2+"px";
login.style.top = (bodySize[1]/2-100-i*i)+"px";
login.style.width = i*i*4 + "px";
login.style.height = i*i*1.5+ "px";
if(i<=10){
i++;
setTimeout("popChange("+i+")",10);//设置超时10毫秒
}
}
//打开DIV层
function open()
{
change();
showLogin();
popCoverDiv()
void(0);//不进行任何操作,如：<a href="#">aaa</a>
}
//关闭DIV层
function close(){
M(‘login‘).style.display = ‘none‘;
M("cover_div").style.display = ‘none‘;
void(0);
}
</script>
</head>
<body>
<a href="javascript:open();">登陆</a>
<div id="login">
<span>用户登陆</span>
<div id="panel">
<lable>用户名: </lable><input type="text" size="20" />
<lable>密码: </lable><input type="password" size="20">
<input type="checkbox" /><lable>登陆</lable>
</div>
<input type="button" value="提交" />
<a href="javascript:close();">关闭</a>
</div>
</body>
</html>