I searched for this question and found there is a no answer on Stackoverflow.. So I decided to answer it...
This question helps if you need to get the start/end of n
//Last week (get current week array list from momentjs)
var sd = moment(currentWeekFd[0]).subtract(7, 'days').format();
var ed = moment(currentWeekEd[6]).subtract(7, 'days').format();
var lastWeekStratDay = moment(sd).format('YYYY-MM-DD');
var lastWeekEndDay = moment(ed).format('YYYY-MM-DD');
console.log(lastWeekStratDay +', '+ lastWeekEndDay)
//Next week
var sd = moment(currentWeekFd[0]).add(7, 'days').format();
var ed = moment(currentWeekEd[6]).add(7, 'days').format();
var nextWeekStratDay = moment(sd).format('YYYY-MM-DD');
var nextWeekEndDay = moment(ed).format('YYYY-MM-DD');
console.log(nextWeekStratDay +', '+ nextWeekEndDay)