check for the existence of a specific part of a date

[dulyts]

Is your feature request related to a problem? Please describe.
I sometimes work with ISO dates like "2015-04", but when display with toLocaleString(DateTime.DATE_SHORT) represented as 2015. 04. 01. (with 'HU' locale)

Describe the solution you'd like
Should be great a function (e.g has("day")) to validate that the parsed date contains specific part

const date = DateTime.fromISO("2015-04");
date.toLocaleString({
  year: "2-digit",
  month: date.has("month") ? "2-digit" : undefined,
  day: date.has("day") ? "2-digit" : undefined,
}); // 2015. 04.

OR
toLocaleString just skip "empty" parts

const date = DateTime.fromISO("2015-04");
date.toLocaleString(DateTime.DATE_SHORT); // 2015. 04.

[diesieben07]

At the moment this kind of thing is not possible with Luxon. Internally there is an object representation of the parsed parts (similar to the input for fromObject, i.e. an object like { year: 2015, day: 4 }), however this object is not exposed.

However, even if this was exposed, a DateTime object will always have all its parts. DateTime represents an instant in time, not a "bag of units", so you can't have a "DateTime without a day", because every point in time obviously has a day.

It would be possible for Luxon to expose the parsed object representation, i.e. allow parsing 2025-04 into { year: 2025, month: 4 }. Then you could analyze the keys and decide which units to skip. But I am not sure what the best API for this would look like.

May I ask what your use-case for this is?

[dulyts]

the parsed object representation sounds good for me.
the workaround what I made currently:

const getFormat = (dateStr) => {
  switch(dateStr.length) {
    case 4:
      return  { year: "numeric" };
    case 6:
    case 7:
      return  { year: "numeric", month: numeric };
    default:
      return DateTime.DATE_SHORT;
  }
}
const date = DateTime.fromISO(dateStr);
date.toLocaleString(getFormat(dateStr));

this is necessary because I need to be able to display the dates of past events, sometimes only the year or year and month are known.

[diesieben07]

I will keep this in mind for Luxon 4 so maybe we'll have a better API there.