Get the maximum z-index of an element's ancestors

getMaxZIndex.js

var getMaxZIndex = function (element, maxZIndex) {
  var maxZIndex = maxZIndex || 0;
  var zIndex = element.css('z-index');
  if (zIndex !== 'auto') {
    maxZIndex = Math.max(maxZIndex, zIndex);
  }
  var parent = element.parent();
  if (parent[0].nodeName === 'HTML') {
    return maxZIndex;
  } else {
    return getMaxZIndex(parent, maxZIndex);
  }
};