How to get country specific formatting rules? - d3.js

Question

I am currently building a workflow for vega lite API and want to parametrize the choice of a locale.
So I want the user to specify her country code by providing a IETF language tag like "us-En" or "fr-FR" and from that I want to obtain the country specific formatting rules (see below for the format I need).
E.g., I am looking for a function, which produces the following output for different country codes:
function getLocaleFormats(countryCode) {
if (countryCode === "de-DE") {
return {
"decimal": ",",
"thousands": ".",
"grouping": [3],
"currency": ["€", ""],
"dateTime": "%a %b %e %X %Y",
"date": "%d.%m.%Y",
"time": "%H:%M:%S",
"periods": ["AM", "PM"],
"days": ["Sonntag", "Montag", "Dienstag", "Mittwoch", "Donnerstag", "Freitag", "Samstag"],
"shortDays": ["So", "Mo", "Di", "Mi", "Do", "Fr", "Sa"],
"months": ["Januar", "Februar", "März", "April", "Mai", "Juni", "Juli", "August", "September", "Oktober", "November", "Dezember"],
"shortMonths": ["Jan", "Feb", "Mär", "Apr", "Mai", "Jun", "Jul", "Aug", "Sep", "Okt", "Nov", "Dez"]
};
}
}
Any help would be greatly appreciated.

Answer 1

You are looking for the built-in Intl object:
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl/DateTimeFormat/DateTimeFormat
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl/DateTimeFormat/NumberFormat
On instances of these objects you can call resolvedOptions() to get detailed information about the formatting being used on that locale.
Example:
const nf = new Intl.NumberFormat('en-US');
const df = new Intl.DateTimeFormat('en-US');
const nfOptions = nf.resolvedOptions();
const dfOptions = df.resolvedOptions();
console.dir(nfOptions);
console.dir(dfOptions);

Answer 2

I found the references I need, they are in:
https://unpkg.com/d3-format#1/locale/${countryCode}.json
https://unpkg.com/d3-time-format#1/locale/${countryCode}.json
with country code being the IETF language tag like "us-En".
p.s. I noticed these formatting rules are specified in d3.js as vega lite is build upon d3.js, so I added the d3.js and vega lite tags to the question.