JavaScript ES2023: New Features You Should Know

ES2023 (ECMAScript 2023) brought several exciting features to JavaScript that make our code more expressive and powerful. Let’s explore the most important additions.

Array.prototype.findLast() and findLastIndex()

These methods work like find() and findIndex(), but they search from the end of the array backwards.

const numbers = [1, 2, 3, 4, 5, 4, 3, 2, 1];

// Find the last even number
const lastEven = numbers.findLast(n => n % 2 === 0);
console.log(lastEven); // 2

// Find the index of the last even number
const lastEvenIndex = numbers.findLastIndex(n => n % 2 === 0);
console.log(lastEvenIndex); // 7

Array.prototype.toReversed(), toSorted(), and with()

These new methods return a new array instead of modifying the original, promoting immutable programming patterns.

const fruits = ['banana', 'apple', 'cherry'];

// Non-mutating reverse
const reversed = fruits.toReversed();
console.log(reversed); // ['cherry', 'apple', 'banana']
console.log(fruits); // ['banana', 'apple', 'cherry'] (unchanged)

// Non-mutating sort
const sorted = fruits.toSorted();
console.log(sorted); // ['apple', 'banana', 'cherry']

// Non-mutating replacement
const newFruits = fruits.with(1, 'orange');
console.log(newFruits); // ['banana', 'orange', 'cherry']

Hashbang Grammar

You can now use hashbang (#!) at the beginning of JavaScript files to specify the interpreter.

#!/usr/bin/env node

console.log("Hello from a JavaScript executable!");

Symbols as WeakMap Keys

WeakMaps can now use symbols as keys, not just objects.

const sym = Symbol('key');
const wm = new WeakMap();
wm.set(sym, 'value');
console.log(wm.get(sym)); // 'value'

Impact on Development

These features contribute to:

• Better immutability patterns with non-mutating array methods
• More expressive code with findLast methods
• Improved tooling support with hashbang syntax
• Greater flexibility with symbol WeakMap keys

ES2023 continues JavaScript’s evolution toward more developer-friendly and powerful language features.