This indicates whether the Day.js object is before the other supplied date-time.
dayjs().isBefore(dayjs('2011-01-01')) // default milliseconds
If you want to limit the granularity to a unit other than milliseconds, pass it as the second parameter. In that case, the comparison respects the given unit and the units above.
dayjs().isBefore('2011-01-01', 'month') // compares month and year
Units are case insensitive, and support plural and short forms.