day.js

Monday of last week

dayjs().startOf('isoWeek').subtract(7, 'day')

Sunday of last week

dayjs().startOf('week');

Monday of two weeks prior

dayjs().startOf('isoWeek').subtract(14, 'day');

First day of last month

dayjs().subtract(1, 'month').startOf('month');dayjs(
new Date(today.getFullYear(), today.getMonth() - 1, 1).toString()
);

Last day of last month

dayjs().subtract(1, 'month').endOf('month');dayjs(
new Date(today.getFullYear(), today.getMonth(), 0).toString()
);

First day of two months prior

dayjs().subtract(2, 'month').startOf('month');dayjs(
new Date(today.getFullYear(), today.getMonth() - 2, 1).toString()
);