百度地图覆盖物id

前几天做了一个百度地图的功能，需要根对做大量的覆盖物删除添加：

var os = map.getOverlays();

for(var i = 0; i < os.length ; i++){
             //不同覆盖物调用不同的计算方法
             switch (os[i].toString()) {
                 case "[object Polyline]":
                     //
                     break;
                 case "[object Polygon]":
                     //
                     break;
                 case "[object Circle]":
                     //
                     break;
                 case "[object Marker]":
                     //
                     break;
            }
}