String.prototype.localeCompare()

const a = "rserv"; // With accents, lowercase
const b = "RESERVE"; // No accents, uppercase

console.log(a.localeCompare(b));
// : 1
console.log(a.localeCompare(b, "en", { sensitivity: "base" }));
// : 0

localeCompare(compareString)
localeCompare(compareString, locales)
localeCompare(compareString, locales, options)

//  "a"  "c" 
"a".localeCompare("c"); // -2  -1 

//  "check"  "against" 
"check".localeCompare("against"); // 2  1 

// "a" "a"  0 
"a".localeCompare("a"); // 0

const items = ["rserv", "Premier", "Clich", "communiqu", "caf", "Adieu"];
items.sort((a, b) => a.localeCompare(b, "fr", { ignorePunctuation: true }));
// ['Adieu', 'caf', 'Clich', 'communiqu', 'Premier', 'rserv']

function localeCompareSupportsLocales() {
  try {
    "foo".localeCompare("bar", "i");
  } catch (e) {
    return e.name === "RangeError";
  }
  return false;
}

console.log("".localeCompare("z", "de")); // :    a 
console.log("".localeCompare("z", "sv")); // :    z 

//    base letter  a
console.log("".localeCompare("a", "de", { sensitivity: "base" })); // 0

//    a  base letter 
console.log("".localeCompare("a", "sv", { sensitivity: "base" })); // 

//  "2" > "10"
console.log("2".localeCompare("10")); // 1

// options 
console.log("2".localeCompare("10", undefined, { numeric: true })); // -1

// 
console.log("2".localeCompare("10", "en-u-kn-true")); // -1