JavaScript Array.reverse() and toReversed() - Reverse Array Order

Understanding reverse() and toReversed()

Array.reverse()

Reverses the array in place and returns the same array reference:

const arr = [1, 2, 3, 4, 5];
const result = arr.reverse();
// arr: [5, 4, 3, 2, 1]
// result === arr: true (same reference!)

toReversed() (ES2023)

Returns a new reversed array without modifying the original:

const arr = [1, 2, 3, 4, 5];
const reversed = arr.toReversed();
// reversed: [5, 4, 3, 2, 1]
// arr: [1, 2, 3, 4, 5] (unchanged)

Pre-ES2023: Copying Before Reverse

// Spread and reverse
const reversed = [...arr].reverse();

// slice and reverse
const reversed = arr.slice().reverse();

Practical Examples

Reverse a string:

const reversed = "hello".split("").reverse().join("");
// reversed: "olleh"

Note: This approach does not handle Unicode properly. For emoji-safe reversal:

const reversed = [...str].reverse().join("");

Palindrome check:

function isPalindrome(str) {
  const clean = str.toLowerCase().replace(/[^a-z0-9]/g, "");
  return clean === [...clean].reverse().join("");
}
isPalindrome("racecar");    // true
isPalindrome("A man, a plan, a canal: Panama"); // true

Display recent items first:

// Show newest messages at top
const recentFirst = messages.toReversed();

Performance

reverse() is O(n) and operates in-place (no extra memory). toReversed() is also O(n) but allocates a new array. Both are very fast for typical array sizes.