设置一个Map 对象的缓存，get 回来怎么就变成了一个array

// 例如  

const createType = function(name,index,list){  
    var type = new Object();  
    type.name=name;  
    type.curIndex = index;  
    if(list){  
        type.list = list;  
    }else{  
        var arr = new Array();  
        type.list = arr;  
    }  
    return type;  
}  

var map = new Map();  
map.set("type1",createType("type1",0,new Array()));  
map.set("type2",createType("type1",0,new Array()));  
map.set("type3",createType("type1",0,new Array()));  
map.set("type4",createType("type1",0,new Array()));  
//放入缓存  
var mapKey = "map";  
uni.setStorageSync(mapKey , map);  

var map= uni.getStorageSync(mapKey );  

console.log("map:",map instanceof Map);    // false  
console.log("map:",map instanceof Array);   //true  

这有点尴尬呀，取处理居然变成一个Array 了 算bug吗？？？