Judge whether the node's child nodes being loaded asynchronously.
Do not initialize or modify it, it is created by the zTree.
true means: the node's child nodes is being loaded asynchronously
false means: the node's child nodes is not being loaded asynchronously
var treeObj = $.fn.zTree.getZTreeObj("tree");
var sNodes = treeObj.getSelectedNodes();
if (sNodes.length > 0) {
var isAjaxing = sNodes[0].isAjaxing;
}