create session times with between two shift times

createSessionsGroups.ts

import moment from 'moment'

function createSessionsGroups(duration: number, shiftStart: moment.Moment, shiftEnd: moment.Moment, initialSessions: Array<string> = []): Array<string> {
  const sessions: Array<string> = [...initialSessions]

  const sessionStart = moment().hour(shiftStart.hour()).minute(shiftStart.minute())

  const sessionEnd = sessionStart.clone().add(duration, 'minute')

  sessions.push(sessionStart.format('HH:mm'))

  const isBefore = sessionEnd.isBefore(shiftEnd)

  if (isBefore) {
    return createSessionsGroups(duration, shiftStart.add(duration, 'minute'), shiftEnd, sessions)
  }

  return sessions
}

const timeSlots = [
  {
    start: '09:00:00.0000000',
    end: '18:00:00.0000000',
  },
]

let sessions: Array<string> = []

timeSlots.forEach(({ start, end }) => {
  const duration = 15
  const startTime = moment(start, 'hh.mm.ss.sssssss')
  const endTime = moment(end, 'hh.mm.ss.sssssss')

  const sesions = createSessionsGroups(duration, startTime, endTime)

  sessions.push(...sesions)
})

// output: [
//   '09:00',
//   '09:15',
//   '09:30',
//   '09:45',
//   '10:00',
//   '10:15',
//   '10:30',
//   '10:45',
//   '11:00',
//   '11:15',
//   '11:30',
//   '11:45',
//   '12:00',
//   '12:15',
//   '12:30',
//   '12:45',
//   '13:00',
//   '13:15',
//   '13:30',
//   '13:45',
//   '14:00',
//   '14:15',
//   '14:30',
//   '14:45',
//   '15:00',
//   '15:15',
//   '15:30',
//   '15:45',
//   '16:00',
//   '16:15',
//   '16:30',
//   '16:45',
//   '17:00',
//   '17:15',
//   '17:30',
//   '17:45',
// ]