JavaScript树状目录问题 求助

/*
 * list[id] 是保存每个节点信息的数组
 * 2010-4-8 
 */
var list = [];
var tree = function(objName) {
this.title = objName;
this.liNode = [];
this.ulNode = [];
this.str = document.createElement("div");
this.str.innerHTML = this.title;
//将各个图片的路径封装成json格式
this.imgs = {
folderClose:"img/folderclose.gif",
folderOpen:"img/folderopen.gif",
rootFolder:"img/imgfolder.gif",
line:"img/line.gif",
join:"img/join.gif",
joinButtom:"img/joinbottom.gif",
emty:"img/empty.gif",
noLine_minus:"img/nolines_minus.gif",
noLine_plus:"img/nolines_plus.gif",
plus:"img/plus.gif",
plusBottom:"img/plusbottom.gif",
line:"img/line.gif",
joinButtom:"img/joinbottom.gif",
page:"img/page.gif"
};
};

//节点ID，父节点ID，节点名字，链接，目标 --->节点信息
tree.prototype.node = function(id,parentId,nodeName,url,target) {
this.id = id;
this.parentId = parentId;
this.nodeName = nodeName;
this.url = (url==null?"javascript:void(0)":url);
this.target = (target==null?"":target);
this.idLength = id.length; //ID的长度
this.hasChild = false; //是否有子节点
this.hasparent = fals