dayjs.duration().clone(); 创建持续时间的克隆。持续时间是不可变的，就像 Day.js 对象一样。尽管如此，这仍然可以让你在某个时间点获得快照。 ¥Create a clone of a duration. Durations are immutable, just like Day.js object objects. Still, this lets you get a snapshot, at some point in time.
