我有一个对象，我想获取它的长度（看看里面有多少个对象）。创建对象的代码如下：

 var threeDSCards = [];
 var card = {}

card[0] = {cardid: 10127, cardnumber: 411111111111, expMonth: 02, expYear: 18};                    
card[1] = {cardid: 10128, cardnumber: 411111111111, expMonth: 01, expYear: 19};

threeDSCards.push(card);

代码在控制台中输出对象的以下内容：

[{
"0":{"cardid":10127,"cardnumber":411111111111,"expMonth":2,"expYear":18},
"1":{"cardid":10128,"cardnumber":411111111111,"expMonth":1,"expYear":19}
}]

我期望长度为 2，因为对象中存储了 2 张卡