function count() {
    var zTree = $.fn.zTree.getZTreeObj("classpurview");
    checkCount = zTree.getCheckedNodes(true);

    var classpurview = "";
    for(var i=0;i<checkCount.length;i++) {
   classpurview += "," + checkCount[i].id
    }
    alert(classpurview);
}