[]如何在游戏入口处获取对象的子对象

在游戏入口实例化玩一个加载TiledMap地图的类(loadMap)后，想通过该对象获取到被加载地图的一个MapLayer层。也就是说，加载TiledMap和获取该地图的MapLayer（某一层）都放到一个类里面，只要通过实例化的对象就能直接调用MapLayer.具体怎么实现呢。获取地图层一定要在_proto.mapLoaaded里面吗？

/*

* name;

*/

var TiledMap = Laya.TiledMap;

var Rectangle = Laya.Rectangle;

var Handler = Laya.Handler;

var Sprite = Laya.Sprite;

var MapLayer = Laya.MapLayer;

var loadMap = (function (_super) {

    function loadMap() {

        loadMap.super(this);

    }

    Laya.class(loadMap,"loadMap",_super);

    var _proto = loadMap.prototype;

    _proto.init = function() {

        this.num = "";

        this.map = new TiledMap();

    }

    _proto.showMap = function(num) {

        this.num = num;

        this.map.createMap("map/level/mota_map" + num + ".json",new Rectangle(0,0,448,448),Handler.create(this,this.mapLoaded));}

     

    _proto.mapLoaded = function(){

        this.pass = this.map.getLayerByIndex(0);//获取通行层

        console.log(this.pass);

    }

    _proto.getLayer = function() {

        this.floor = this.map.getLayerByIndex(0);//获取通行层

        console.log(this.pass);

    }

    console.log(this.map)

    return loadMap;

})(Sprite);

**游戏主入口**

var Main = (function (){

    (function Main(){

        Laya.init(448,448);

        var map1 = new loadMap();

        map1.init();

        map1.showMap("3");

        map1.getLayer();

        console.log(map1.num);

        console.log(map1);

        console.log(map1.pass);

        console.log(map1.getLayer);

    })();

    return Main;

})();