在Jquery中让一个容器div显示在屏幕正中央

非常简单就实现了，代码不用解释，很容易懂的

//request data for centering
var windowWidth = document.documentElement.clientWidth;
var windowHeight = document.documentElement.clientHeight;
var popupHeight = $("#popupContact").height();
var popupWidth = $("#popupContact").width();
//centering
$("#popupContact").css({
"position": "absolute",
"top": windowHeight/2-popupHeight/2,
"left": windowWidth/2-popupWidth/2
});