How to get the beginning and end of the day with moment?

I would like to get the beginning and end of the current day (and accessorily of tomorrow by .add(1, 'day')) using moment.

What I am getting now is

now = moment()
console.log('now ' + now.toISOString())
console.log('start ' + now.startOf('day').toISOString())
console.log('end ' + now.endOf('day').toISOString())

<script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.22.1/moment.js"></script>

This outputs right now

now 2018-04-18T21:20:02.010Z
start 2018-04-17T23:00:00.000Z
end 2018-04-18T22:59:59.999Z

Since the times are shifted by an hour, I believe that this is something related to timezones, though I fail to understand how this can be relevant: no matter the time zone, the day in that timezone begins right after midnight today and ends right before midnight today.

It is giving you midnight local time, but you're printing it out in zulu time. Try using toString instead, it will print the time out in local time.

now = moment()
console.log('now ' + now.toString())
console.log('start ' + now.startOf('day').toString())
console.log('end ' + now.endOf('day').toString())

<script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.22.1/moment.js"></script>

If you want to start with Monday you have to use this one moment().startOf('isoWeek');

console.log({
  from_date: moment().startOf('isoWeek').toString(),
  today: moment().toString(),
  to_date: moment().endOf('isoWeek').toString(),
});