What are the new features in ES2023?

ES2023 (ECMAScript 14) Key Features

1. Array.prototype.toSorted()

Returns a new sorted array without modifying the original (non-mutating).

const arr = [3, 1, 2];
const sorted = arr.toSorted(); // [1, 2, 3]
console.log(arr); // [3, 1, 2] (unchanged)

2. Array.prototype.toReversed()

Returns a new reversed array without modifying the original.

const arr = [1, 2, 3];
const reversed = arr.toReversed(); // [3, 2, 1]
console.log(arr); // [1, 2, 3] (unchanged)

3. Array.prototype.toSpliced()

Returns a new array with splice applied without modifying the original.

const arr = [1, 2, 3, 4];
const result = arr.toSpliced(1, 2, 'a', 'b'); // [1, 'a', 'b', 4]
console.log(arr); // [1, 2, 3, 4] (unchanged)

4. Array.prototype.with()

Returns a new array with one element replaced without modifying the original.

const arr = [1, 2, 3];
const result = arr.with(1, 99); // [1, 99, 3]
console.log(arr); // [1, 2, 3] (unchanged)

5. Array.prototype.findLast() and findLastIndex()

Search from the end of the array.

const arr = [1, 2, 3, 4, 5];
arr.findLast(n => n % 2 === 0);      // 4
arr.findLastIndex(n => n % 2 === 0); // 3

6. Hashbang Grammar (#!)

Allows #! at the start of scripts for Unix shebang support.

#!/usr/bin/env node
console.log('Hello!');

7. WeakMap Keys with Symbols

const key = Symbol('key');
const map = new WeakMap();
map.set(key, 'value');

Summary

ES2023's highlight is a set of non-mutating array methods that make functional programming more convenient and prevent accidental mutation of original data.