레이어 팝업 가운데 정렬

$(document).ready(function() {

  $.fn.center = function () {

    this.css("position","absolute");

    this.css("top", Math.max(0, (($(window).height() - $(this).outerHeight()) / 2) + $(window).scrollTop()) + "px");

    this.css("left", Math.max(0, (($(window).width() - $(this).outerWidth()) / 2) + $(window).scrollLeft()) + "px");

    return this;

  }

  $("body").append("<div id='payIngPopup'></div>");

  $("#popLayer").show();

  $("#popLayer").center();

});

<div id="popLayer" style="display:none;z-index: 9999;">