var popupStatus = 0;
//loading popup with jQuery magic!
function loadPopup(){
//loads popup only if it is disabled
if(popupStatus==0){
$("#backgroundPopup").css({
"opacity": "0.7"
});
$("#backgroundPopup").fadeIn("slow");
$("#popupContact").fadeIn("slow");
popupStatus = 1;
}
}
//disabling popup with jQuery magic!
function disablePopup(){
//disables popup only if it is enabled
if(popupStatus==1){
$("#backgroundPopup").fadeOut("slow");
$("#popupContact").fadeOut("slow");
popupStatus = 0;
}
}
//centering popup
function centerPopup(){
//request data for centering
var browser=navigator.userAgent;
var windowWidth = document.documentElement.clientWidth;
var windowHeight = document.documentElement.clientHeight;
var stop="";
var sleft="";
if(browser.indexOf('Chrome')!=-1){
stop=document.body.scrollTop;
sleft=document.body.scrollLeft;
}
else{
stop=document.documentElement.scrollTop;
sleft=document.documentElement.scrollLeft;
}
// windowWidth+=document.body.scrollLeft;
// windowHeight+=document.body.scrollTop;
var popupHeight = $("#popupContact").height();
var popupWidth = $("#popupContact").width();
//centering
$("#popupContact").css({
"position": "absolute",
"top": windowHeight/2-popupHeight/2+stop,
"left": windowWidth/2-popupWidth/2+sleft
});
//only need force for IE6
//背景色
$("#backgroundPopup").css({
"height": windowHeight
});
}
//調用彈出框事件
function bb(str){
$("#download").show();
centerPopup();
loadPopup();
//CLOSING POPUP
//Click the x event!
$("#popupContactClose").click(function(){
disablePopup();
});
//Click out event!，點擊背景事件
$("#backgroundPopup").click(function(){
disablePopup();
});
//Press Escape event!
$(document).keypress(function(e){
if(e.keyCode==27 && popupStatus==1){
disablePopup();
}
});
}

<div id="download" style="display: none;">
<div id="popupContact">
<!--自己的 HTML（body中）-->
</div>
<div id="backgroundPopup"></div>
</div>
</div>