Locale and specific date format with Moment.js

Okay. This is a little awful, but you knew it was going to be.

First, you can access the actual format string for (for instance) 'L':

var formatL = moment.localeData().longDateFormat('L');

Next, you can perform some surgery on it with judicious regex replacement:

var formatYearlessL = formatL.replace(/Y/g,'').replace(/^\W|\W$|\W\W/,'');

(Which is to say: Remove YYYY, plus the orphaned separator left by its removal)

Then you can use your new format string in a moment format call:

someDate.format(formatYearlessL);

This necessarily makes some assumptions:

• The order of the month + day numeric format for a locale matches the order for the year + month + day format for that locale, with the year removed.
• The short form uses separators only between month and day (no leading / trailing separators).
• The separator for a short numeric date format is always non-alphanumeric.
• The format consists of numeric elements and separators, rather than a sentence-form format with articles (see RGPT's comment below about Spanish and Portugese, which will also apply to long formats in some other languages).

On a quick review of locale/*.js, these assumptions hold true for every locale file I examined, but there may be some locales that violate them. (ETA: a comment below points out that a German short date format violates the second assumption)

As an additional important caveat, this is likely to be fragile. It is entirely possible that a future version of moment.js will change the location of the data currently in longDateFormat...

As far as I understand, you can change the date format(without year) for specific languages using MomentJS properties https://momentjs.com/docs/#/customization/long-date-formats/

Example:

moment.updateLocale('en', {
  longDateFormat: {
    LLL: "MMMM Do, LT", // Oct 6th, 4:27 PM
  }
});

moment.updateLocale('ru', {
  longDateFormat: {
    LLL : 'D MMMM, HH:mm', // 6 окт., 16:27
  }
});