ISO 星期

获取或设置 ISO 星期，其中 1 为星期一，7 为星期日。

¥Gets or sets the ISO day of the week with 1 being Monday and 7 being Sunday.

This requires the IsoWeek plugin to work

dayjs.extend(isoWeek)

dayjs().isoWeekday() // gets the current ISO day of the week
dayjs().isoWeekday(1); // Monday