Does it mutate 😱

Array.prototype.toLocaleString

No mutation

Description

The toLocaleString() method of Array instances returns a string representing the elements of the array. The elements are converted to strings using their toLocaleString methods and these strings are separated by a locale-specific string (such as a comma ",").

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/toLocaleString

Example

const array1 = [1, 'a', new Date('21 Dec 1997 14:12:00 UTC')];
const localeString = array1.toLocaleString('en', { timeZone: 'UTC' });

console.log(localeString);
// Expected output: "1,a,12/21/1997, 2:12:00 PM",
// This assumes "en" locale and UTC timezone - your results may vary