function centerBox(obj){ var $obj; if(obj instanceof jQuery){ $obj=obj; }else{ $obj=$(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 }); }