如何在递归后正确返回值？

Question

var fs = require("fs");
var path = require("path");

var traversalDir = function(path, directoryJson) {
    fs.readdir(path,function(err, node) {
        // exit if all nodes have no more child.
        if (!node) {
            return directoryJson;
        }
        node.forEach(function(filename) {
            fs.stat(path + "/" + filename, function(err, info) {
                // use the parent directory as the book name
                var book = path.split("/").pop();
                if (info.isDirectory()) {
                    // go dig deeper!
                    traversalDir(path + "/" + filename, directoryJson);
                } else {
                    try {
                        // push the files inside the book directory into
                        // the directoryJson
                        directoryJson[book].push(filename);
                    } catch (err) {
                        // create the book node in the directoryJson 
                        directoryJson[book] = Array();
                        directoryJson[book].push(filename);
                        console.log(JSON.stringify(directoryJson));
                    }
                }
            });
        });
    });
};

var root = path.join(__dirname);
console.log(JSON.stringify(traversalDir(path.join(root), {})));

在console.log完成之前调用的最后一个function(traversalDir)事件！

所以，我最终只能获得{}值。但是，函数中的注销表明函数正常工作。