getWeekEndDays.js

// requires moment.js

var getWeekEndDays = function (year) {
  return new Promise(function (resolve, reject) {
    if (year === undefined) {
      year = moment().year().toString()
    }

    let weekEndsDays = []
    let start = moment(year + '-01-01').startOf('year')
    let end = moment(year + '-01-01').endOf('year')

    for (var day = moment(start); day.isBefore(end); day.add(1, 'days')) {
      if (day.weekday() === 6 || day.weekday() === 0) {
        weekEndsDays.push(day.toDate())
      }
    }
    resolve(weekEndsDays)
  })
}