KnockoutJS - 创建对象不起作用

我正在做一个带有菜单和子菜单的导航列表。

我有以下结构：

function Menu(navigation) {
    this.NavigationUrl = ko.observable(navigation.NavigationUrl);
    this.NavigationTitle = ko.observable(navigation.NavigationTitle);
    this.NavigationDescription = ko.observable(navigation.NavigationDescription);
    var mappedChildren = ko.utils.arrayMap(navigation.Children, function (child) {
        return new Menu(child);
    });
    this.Children = ko.observableArray(mappedChildren);
}
function DashboardViewModel() {
    var self = this;
    self.LoggedUser = ko.observable("");
    self.Navigations = ko.observableArray([]);
    $.get('/Home/DashboardDependencies', {}, function (result) {
        self.LoggedUser(result.LoggedUser);
        var mappedNavigations = ko.utils.arrayMap(result.Navigations, function (item) {
            var menu = new Menu(item);
            // When I alert item, the result appears properly:
            // { "NavigationTitle": "blah", "NavigationDescription": "bleh" [...] }
            alert(JSON.stringify(item));
            // But when I alert the new menu object, the result doesn't appear:
            // Just: "{}"
            alert(JSON.stringify(menu));
            return menu;
        });
        self.Navigations = mappedNavigations;
    });
}
ko.applyBindings(new DashboardViewModel());

所以，检查一下。当我尝试提醒项目变量时，结果显示正确。当我尝试提醒新的 Menu 对象时，结果只显示{}.为什么会这样？

谢谢大家的帮助！