Unix 时间戳

这将返回 Day.js 对象的 Unix 时间戳（自 Unix 纪元以来的秒数）。

¥This returns the Unix timestamp (the number of seconds since the Unix Epoch) of the Day.js object.

dayjs('2019-01-25').unix() // 1548381600

该值被取整到最接近的秒，并且不包括毫秒分量。

¥This value is floored to the nearest second, and does not include a milliseconds component.