INTL

// 1
const date = new Date(Date.UTC(2020, 11, 20, 3, 23, 16, 738));
console.log(new Intl.DateTimeFormat('pl-PL', {dateStyle: 'full'}).format(date));
// niedziela, 20 grudnia 2020

// 2
const vehicles = ['Motor', 'bus', 'samochód'];
const formatter = new Intl.ListFormat('pl', { style: 'long', type: 'conjunction' });
console.log(formatter.format(vehicles));
// Motor, bus i samochód
const formatter2 = new Intl.ListFormat('pl', { style: 'short', type: 'disjunction' });
console.log(formatter2.format(vehicles));
// Motor, bus lub samochód


// 3 
const number = 123456.789;

console.log(new Intl.NumberFormat('pl-PL', { style: 'currency', currency: 'PLN' }).format(number));
// expected output: "123.456,79 zł

// 4 
// Create a relative time formatter in your locale
// with default values explicitly passed in.
const rtf = new Intl.RelativeTimeFormat("pl", {
    localeMatcher: "best fit", // other values: "lookup"
    numeric: "always", // other values: "auto"
    style: "long", // other values: "short" or "narrow"
});

// Format relative time using negative value (-1).
console.log(rtf.format(-1, "day"));
// 1 dzień temu

// Format relative time using positive  value (1).
console.log(rtf.format(1, "day"));
// za jeden dzień