callback with binary tree tranversal

test774.js

function ObjectId(str) {
    return str;
}

var Subject = {
    "data": {
        "4f5ca201e7a3792f5e000003": {
            "_id": ObjectId("4f5ca201e7a3792f5e000003"),
            "childId": ObjectId("4f5ca5939da509475e000003"),
            "name": "資產類",
            "parentId": "-1",
            "siblingId": ObjectId("4f5ca20ce7a3792f5e000005"),
            "sn": "1000"
        },
        "4f5ca20ce7a3792f5e000005":{
            "_id": ObjectId("4f5ca20ce7a3792f5e000005"),
            "name": "負債類",
            "parentId": "4f5ca201e7a3792f5e000003",
            "siblingId": ObjectId("4f5ca215e7a3792f5e00000a"),
            "sn": "2000"
        },
        "4f5ca215e7a3792f5e00000a":{
            "parentId": "4f5ca20ce7a3792f5e000005",
            "name": "業主權益類",
            "sn": "3000",
            "_id": ObjectId("4f5ca215e7a3792f5e00000a")
        },
        "4f5ca5939da509475e000003":{
            "parentId": "4f5ca201e7a3792f5e000003",
            "name": "流動資產",
            "sn": "1100",
            "_id": ObjectId("4f5ca5939da509475e000003")
        },
        "4f5ca7a19da509475e000005":{
            "parentId": "4f5ca5939da509475e000003",
            "name": "基金及投資",
            "sn": "1100",
            "_id": ObjectId("4f5ca7a19da509475e000005")
        }
    },
    "findOne": function(qry,cb) {
        for(var i in this.data) {
            if(this.data[i].parentId==="-1") {
                cb(false, this.data[i]);
                return;
            }
        }
        cb(true);
    },
    "findById": function(qry,cb) {
        for(var i in this.data) {
            if(this.data[i]._id===qry._id) {
                cb(false, this.data[i]);
            }
        }
        cb(true);
    }
};

var wait = function (cb) {
    var payload = [];
    return {
        next: function (data) {
            if(data) payload.push(data);
        },
        stop: function(end) {
            if(end)
                cb(payload);
        }
    };
};

var Tree = function() {
    var subArray = [];

    var getRootId = function(cb) {
        Subject.findOne({
            parentId: -1
        }, function(err, node) {
            if(!err) {
                cb(node._id);
            }
        });
    };

    var preOrder = function(nodeId, cb) {
        Subject.findById({
            _id: nodeId
        }, function(err, node) {
            if (err) return;
            if (node !== undefined) {
                subArray.push({
                    name: node.name,
                    sn: node.sn,
                    id: node._id
                });
                cb.next(JSON.stringify(subArray));
                preOrder(node.childId, cb);
                preOrder(node.siblingId, cb);
                subArray.pop();
                cb.stop(node.parentId==='-1');
            }
        });
    };

    return {
        getSubArray: function(cb) {
            getRootId(function(nodeId) {
                preOrder(nodeId,cb);
            });
        }
    };
};
var tree = Tree();

tree.getSubArray(wait(function(subs) {console.log(subs);}));