js不能获取隐藏的div的宽度只能先显示后获取

<div class="jb51code">
<pre class="brush:js;">
var tipsWidth = $(".Loading").css("width").replace("px","") //先获取
var windowWidth = $(window).width();
$(".Loading").css({ "display": "block" }); //再显示
$(".Loading").css({ "left": (windowWidth - tipsWidth) / 2 + "px" });