即使加载了excheck的js，复选框依然不显示，为什么？

<script type="text/javascript">
var setting = {
check: {enable: true,chkStyle: "checkbox",chkboxType: { "Y": "ps"+"", "N": ""+"ps" }}, data: {simpleData: {enable: true}},callback: {onCheck: onCheck}
};var zNodes =[
{ id:'001', pId:'001', name:'行政管理', checked:true},
{ id:'001001', pId:'001', name:'文档管理', checked:true},
{ id:'001001001', pId:'001', name:'文件查询', checked:true},
{ id:'001001002', pId:'001', name:'文件上传', checked:true},
{ id:'001001003', pId:'001', name:'简报纪要查询', checked:true},
{ id:'001001004', pId:'001', name:'简报纪要上传', checked:true},
{ id:'001002', pId:'001', name:'人员管理', checked:true},
{ id:'001002001', pId:'001', name:'部门登记', checked:true},
{ id:'001002002', pId:'001', name:'部门查询', checked:true},
{ id:'001002003', pId:'001', name:'人员情报登记', checked:true},
{ id:'001002004', pId:'001', name:'人员情报查询', checked:true},
{ id:'001002005', pId:'001', name:'休假登记', checked:true},
{ id:'001002006', pId:'001', name:'休假查询', checked:true},
{ id:'001002007', pId:'001', name:'休假统计确认', checked:true},
{ id:'001002008', pId:'001', name:'休假规定登记', checked:true},
{ id:'001002009', pId:'001', name:'休假规定查询', checked:true},
{ id:'001003', pId:'001', name:'值班签到', checked:true},
{ id:'001003001', pId:'001', name:'签到排版登记', checked:true},
{ id:'001003002', pId:'001', name:'签到排版查询', checked:true},
{ id:'001003003', pId:'001', name:'值班签到', checked:true},
{ id:'001003004', pId:'001', name:'签到统计', checked:true},
{ id:'001004', pId:'001', name:'内部通知', checked:true},
{ id:'001004001', pId:'001', name:'内部通知登记', checked:true},
{ id:'001004002', pId:'001', name:'内部通知查询', checked:true},
{ id:'001005', pId:'001', name:'督察督办', checked:true},
{ id:'001005001', pId:'001', name:'督察督办登记', checked:true},
{ id:'001005002', pId:'001', name:'督察督办查询', checked:true},
{ id:'002', pId:'002', name:'运行管理', checked:true},
{ id:'002001', pId:'002', name:'服务投诉', checked:true},
{ id:'002001001', pId:'002', name:'服务投诉登记', checked:true},
{ id:'002001002', pId:'002', name:'服务投诉查询', checked:true},
{ id:'002002', pId:'002', name:'巡视管理', checked:true},
{ id:'002002001', pId:'002', name:'巡视任务登记', checked:true},
{ id:'002002002', pId:'002', name:'巡视任务查询', checked:true},
{ id:'002003', pId:'002', name:'设备状态', checked:true},
{ id:'002004', pId:'002', name:'施工管理', checked:true},
{ id:'002005', pId:'002', name:'事项管理', checked:true},
{ id:'002006', pId:'002', name:'机上监管', checked:true},
{ id:'003', pId:'003', name:'航延处置', checked:true},
{ id:'004', pId:'004', name:'设备管理', checked:true},
{ id:'005', pId:'005', name:'系统管理', checked:true}
];
function onCheck(event, treeId, treeNode, clickFlag){
var treeObj = $.fn.zTree.getZTreeObj("treeDemo");
var nodes = treeObj.getCheckedNodes(true);
var Nid = "";
for(var i=0;i<nodes.length;i++){
Nid=Nid+nodes[i].id.toString()+",";
}
document.getElementById('txtMessageValue').value=Nid;
}
function getCheckId()
{
var treeObj = $.fn.zTree.getZTreeObj("treeDemo");
var nodes = treeObj.getCheckedNodes(true);
var Nid = "";
for(var i=0;i<nodes.length;i++)
{
Nid=Nid+nodes[i].id+",";
}
document.getElementById('txtMessageValue').value=Nid;
}
$(document).ready(function(){
$.fn.zTree.init($('#treeDemo'), setting, zNodes);
getCheckId();});
</script>

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