【原创】相对完美的垂直居中popup(modal/dialog)，无需监听window.resize事件

<table class="popup" style="position: absolute; background-color: black; border-radius: 10px; top: 50%; left: 50%;">
<tr>
<td>
<div>
<textarea style="margin:10px;  background-color:azure;  height:150px;width:100px;" contenteditable="true"></textarea>
</div>
</td>
</tr>
</table>

$(function () {
var $popup = $('.popup');
$popup.css({marginLeft: $popup.width() / 2 * -1 + 'px', marginTop: $popup.height() / 2 * -1 + 'px' });
});