Get a list of the start and end dates of the current and the previous month, as ISO 8601 formatted dates. (Power Query)

get-month-boundary-pairs-as-ISO8601.m

// Get a list of the start and end dates of the relative month, as ISO 8601 formatted dates.
//
// E.g.:
// ```
// {
//     "2016-09-01",
//     "2016-09-31"
// }
// ```
//
// Source: <https://gist.github.com/r-k-b/db1eb0e00364cb592e1d8674bb03cb5c>

let
    GetMonthDates = (monthOffset as number) as list => let
        now = DateTime.LocalNow(),
        otherMonth = Date.AddMonths(now, monthOffset),
        month1Start = Date.StartOfMonth(otherMonth),
        month1End = Date.AddDays(Date.EndOfMonth(otherMonth), -1),

        dates = {
            month1Start,
            month1End
        },

        result = List.Transform(
            dates,
            each DateTime.ToText(_, "yyyy-MM-dd")
        )
    in
        result
in
    GetMonthDates