Moment.jsで特定の月のすべての日の配列を生成

// 対象の年月（ここでは2020年8月）
const yearMonth = moment([2020, 7])

// 結果配列
const result = []

const startDayOfMonth = yearMonth.startOf('month').get('date')
const endDayOfMonth = yearMonth.endOf('month').get('date')
for (let d = start; d <= end; d++) {
  const m = moment([yearMonth.get('year'), yearMonth.get('month'), d])
  result.push(m)
}

console.log(result)

//  ["2020-08-01", "2020-08-02", "2020-08-03", "2020-08-04", "2020-08-05", "2020-08-06", "2020-08-07", "2020-08-08", "2020-08-09", "2020-08-10", "2020-08-11", "2020-08-12", "2020-08-13", "2020-08-14", "2020-08-15", "2020-08-16", "2020-08-17", "2020-08-18", "2020-08-19", "2020-08-20", "2020-08-21", "2020-08-22", "2020-08-23", "2020-08-24", "2020-08-25", "2020-08-26", "2020-08-27", "2020-08-28", "2020-08-29", "2020-08-30", "2020-08-31"]

参考

https://momentjs.com/docs/#/parsing/array/
https://momentjs.com/docs/#/manipulating/start-of/