jquery实现网页背景变暗的弹框效果

很多网页的登陆就是在页面上弹出一个登陆框，背景变暗，通过jquery可以实现这个效果：

Javascript代码：

var GB_DONE = false;
var GB_HEIGHT = 400;
var GB_WIDTH = 400;
 
function GB_show(caption, url, height, width) {
  $("GB_window").remove();
  GB_HEIGHT = height || 400;
  GB_WIDTH = width || 400;
  if(!GB_DONE) {
    $(document.body)
      .append("<div id='GB_overlay'></div><div id='GB_window'><div id='GB_caption'></div>"
        + "<img src='../images/close.gif' alt='Close window'/></div>");
    $("#GB_window img").click(GB_hide);
    $("#GB_overlay").click(GB_hide);
    $(window).resize(GB_position);
    GB_DONE = true;
  }
 
  $("#GB_frame").remove();  
//下面的append方法里的内容为弹出框的内容，可以自行设定
  $("#GB_window").append("<div id='GB_frame' align='center'><form id='privilegeform' action="+url+" method='post'><p>&nbsp;&nbsp;&nbsp;名称：<input type='text' name='name' id='name' size='30'></p><p>常量名：<input type='text' name='constantName' id='constantName' size='30'></p><p>&nbsp;&nbsp;&nbsp;URL：&nbsp;<input type='text' name='url' id='url' size='30'></p><p>target：<select style='width:210px' id='target'><option selected='selected' value='_self'>_self</option><option value='_blank'>_blank</option><option value='_parent'>_parent</option><option value='_top'>_top</option></select></p><p>&nbsp;&nbsp;描述：<input type='text' name='description' id='description' size='30'></p><p><input type='button' onclick='enter()' value='确定'><input type='button' onclick='enter()' value='sdf'>&nbsp;<input type='button' value='取消' id='cancer'></p></form></div>");
  $("#GB_caption").html(caption);
  $("#GB_overlay").show();
  $("#cancer").click(GB_hide);
  GB_position();
  $("#GB_window").slideDown("slow");  
}
 
function GB_hide() {
    $("#GB_window").slideUp("slow");
    $("#GB_overlay").hide();
}
 
function GB_position() {
  var de = document.documentElement;
  var w = self.innerWidth || (de&&de.clientWidth) || document.body.clientWidth;
  $("#GB_window").css({width:GB_WIDTH+"px",height:GB_HEIGHT+"px",
    left: ((w - GB_WIDTH)/2)+"px" });
  $("#GB_frame").css("height",GB_HEIGHT - 32 +"px");
}
    alert("sdf");
}

把下面的代码保存为greybox.js文件：

var GB_DONE = false;
var GB_HEIGHT = 400;
var GB_WIDTH = 400;
 
function GB_show(caption, url, height, width) {
  $("GB_window").remove();
  GB_HEIGHT = height || 400;
  GB_WIDTH = width || 400;
  if(!GB_DONE) {
    $(document.body)
      .append("<div id='GB_overlay'></div><div id='GB_window'><div id='GB_caption'></div>"
        + "<img src='../images/close.gif' alt='Close window'/></div>");
    $("#GB_window img").click(GB_hide);
    $("#GB_overlay").click(GB_hide);
    $(window).resize(GB_position);
    GB_DONE = true;
  }
 
  $("#GB_frame").remove();  
  $("#GB_window").append("<div id='GB_frame' align='center'><form id='privilegeform' action="+url+" method='post'><p>&nbsp;&nbsp;&nbsp;名称：<input type='text' name='name' id='name' size='30'></p><p>常量名：<input type='text' name='constantName' id='constantName' size='30'></p><p>&nbsp;&nbsp;&nbsp;URL：&nbsp;<input type='text' name='url' id='url' size='30'></p><p>target：<select style='width:210px' id='target'><option selected='selected' value='_self'>_self</option><option value='_blank'>_blank</option><option value='_parent'>_parent</option><option value='_top'>_top</option></select></p><p>&nbsp;&nbsp;描述：<input type='text' name='description' id='description' size='30'></p><p><input type='button' onclick='enter()' value='确定'><input type='button' onclick='enter()' value='sdf'>&nbsp;<input type='button' value='取消' id='cancer'></p></form></div>");
  $("#GB_caption").html(caption);
  $("#GB_overlay").show();
  $("#cancer").click(GB_hide);
  GB_position();
  $("#GB_window").slideDown("slow");  
}
 
function GB_hide() {
    $("#GB_window").slideUp("slow");
    $("#GB_overlay").hide();
}
 
function GB_position() {
  var de = document.documentElement;
  var w = self.innerWidth || (de&&de.clientWidth) || document.body.clientWidth;
  $("#GB_window").css({width:GB_WIDTH+"px",height:GB_HEIGHT+"px",
    left: ((w - GB_WIDTH)/2)+"px" });
  $("#GB_frame").css("height",GB_HEIGHT - 32 +"px");
}
 
function enter(){
    alert("sdf");
}

CSS代码：

#GB_overlay {
  background-image: url(../images/overlay.png); 
  position: absolute;
  margin: auto;
  top: 0;
  left: 0;
  z-index: 100;
  width:  100%;
  height: 100%;
}
 
* html #GB_overlay {
  background-color: #000;
  background-color: transparent;
  background-image: url(../images/blank.gif);
  filter: progid:DXImageTransform.Microsoft.AlphaImageLoader(src="../images/overlay.png", sizingMethod="scale");
}
 
#GB_window {
  top: 100px;
  left: 0px;
  position: absolute;
  background: #fff;
  border: 5px solid #aaa;
  overflow: auto;
  width: 400px;
  height: 400px;
  z-index: 150;
}
 
#GB_frame {
  border: 0;
  overflow: auto;
  width: 100%;
  height: 378px; 
  font-size:13px;     
}
 
#GB_caption {
  font: 12px bold helvetica, verdana, sans-serif;
  color: #fff;
  background: #888;
  padding: 2px 0 2px 5px;
  margin: 0;
  text-align: left;
}
 
#GB_window img {
  position: absolute;
  top: 2px;
  right: 5px;
  cursor: pointer;
  cursor: hand;
}

在网页中合理运用以上代码。