app-datepicker/dist/helpers/get-resolved-locale.js

A custom datepicker element based on Google's Material Design built from scratch with lit-element

import { INTL_DATE_TIME_FORMAT } from '../constants.js';
export function getResolvedLocale() {
    return (INTL_DATE_TIME_FORMAT &&
        INTL_DATE_TIME_FORMAT().resolvedOptions &&
        INTL_DATE_TIME_FORMAT().resolvedOptions().locale) || 'en-US';
}