uni app x 定义一个数组为啥没有push方法呢?

uni app x
uts

const datas = {}
datas['category'] = new Array<object>()
datas['category']?.push({})

为什么会报错呢?

01:51:03.707 [plugin:uni:app-uts] 编译失败
01:51:03.707 ‌error: Unresolved reference: push‌