showDiv($("#pop")); function showDiv(obj){  $(obj).show();  center(obj);  $(window).scroll(function(){   center(obj);  });  $(window).resize(function(){   center(obj);  }); } 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    });  }