Intl.Collator

console.log(["Z", "a", "z", "ä"].sort(new Intl.Collator("de").compare));
// Expected output: Array ["a", "ä", "z", "Z"]
console.log(["Z", "a", "z", "ä"].sort(new Intl.Collator("sv").compare));
// Expected output: Array ["a", "z", "Z", "ä"]
console.log(
  ["Z", "a", "z", "ä"].sort(
    new Intl.Collator("de", { caseFirst: "upper" }).compare,
  ),
);
// Expected output: Array ["a", "ä", "Z", "z"]

console.log(new Intl.Collator().compare("a", "c")); // → 負の値
console.log(new Intl.Collator().compare("c", "a")); // → 正の値
console.log(new Intl.Collator().compare("a", "a")); // → 0

// in German, ä sorts with a
console.log(new Intl.Collator("de").compare("ä", "z"));
// → 負の値
// in Swedish, ä sorts after z
console.log(new Intl.Collator("sv").compare("ä", "z"));
// → 正の値

// in German, ä has a as the base letter
console.log(new Intl.Collator("de", { sensitivity: "base" }).compare("ä", "a"));
// → 0
// in Swedish, ä and a are separate base letters
console.log(new Intl.Collator("sv", { sensitivity: "base" }).compare("ä", "a"));
// → 正の値