jquery实现弹出层完美居中效果_jquery

function center(obj){
var windowWidth = document.documentElement.clientWidth;
var windowHeight = document.documentElement.clientHeight;
var popupHeight = $(obj).height();
var popupWidth = $(obj).width();
$(obj).css({
"position": "absolute",
"top": (windowHeight-popupHeight)/2+$(document).scrollTop(),
"left": (windowWidth-popupWidth)/2
});
}