Symbols as WeakMap keys

Symbols can now be used as keys in WeakMaps

const sym = Symbol("key");
const weakMap = new WeakMap();
weakMap.set(sym, "value");

Array.fromAsync

Create an array from async iterables

const asyncGen = async function*() { yield 1; yield 2; };
console.log(await Array.fromAsync(asyncGen()));

Array.prototype.toSorted

Sort without mutating original array

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

Hashbang (#!) in JavaScript files

Support for Unix-style shebang

#!/usr/bin/env node
console.log("Hello, Node.js!");

Top-Level Await

Use await outside of async functions

const data = await fetch("https://api.example.com").then(res => res.json());

Object.hasOwn

Check for own properties safely

console.log(Object.hasOwn({a: 1}, "a"));

String.prototype.replaceAll

Replace all occurrences of a substring

console.log("hello hello".replaceAll("hello", "hi"));

Numeric Separators

Improve number readability

const num = 1_000_000;

Nullish Coalescing Operator (??)

Return right operand if left is null or undefined

console.log(null ?? "default"); // "default"

Optional Chaining (?.)

Avoid errors when accessing deep properties

const obj = {};
console.log(obj?.prop?.nested);

Array.prototype.flat

Flatten nested arrays

console.log([1, [2, [3]]].flat(2));

String.prototype.trimStart & trimEnd

Remove whitespace from start or end of a string

console.log("  Hello  ".trimStart());
console.log("  Hello  ".trimEnd());

Object.fromEntries

Transform key-value pairs into objects

console.log(Object.fromEntries([["a", 1], ["b", 2]]));

Optional Catch Binding

Omit catch parameter if unused

try {
throw new Error("Oops");
} catch {
console.log("Error caught");
}

Rest/Spread Properties

Spread objects

const obj = {a: 1, b: 2};
const clone = {...obj};

Promise.prototype.finally

Execute code after promise resolution/rejection

fetchData().finally(() => console.log("Done"));

Asynchronous Iteration

Use for await...of for async iterables

async function process(items) {
for await (const item of items) {
console.log(item);
}
}

RegExp Enhancements

Named capture groups, lookbehind assertions

const regex = /(?<year>\d{4})-(?<month>\d{2})/;
const match = regex.exec("2023-04");
console.log(match.groups.year); // "2023"

Async/Await

Syntactic sugar for promises

async function fetchData() {
return await Promise.resolve("Data");
}

Object.values and Object.entries

Get object values and key-value pairs

console.log(Object.values({a: 1, b: 2}));
console.log(Object.entries({a: 1, b: 2}));

String.prototype.padStart & padEnd

Pad strings with characters

console.log("5".padStart(3, "0")); // "005"
console.log("5".padEnd(3, "0")); // "500"

Trailing commas in function parameters

Allow trailing commas in function definitions

function foo(a, b,) {
console.log(a, b);
}

Shared memory and Atomics

Enable multi-threaded operations

const sharedBuffer = new SharedArrayBuffer(16);
const int32 = new Int32Array(sharedBuffer);
Atomics.store(int32, 0, 123);

Array.prototype.includes

Check if an array contains an element

console.log([1, 2, 3].includes(2)); // true

Exponentiation Operator

** as a shorthand for Math.pow

console.log(2 ** 3); // 8

let and const

Block-scoped variable declarations

let x = 10;
const y = 20;

Arrow Functions

Shorter function syntax with lexical this

const add = (a, b) => a + b;

Template Literals

String interpolation using backticks

const name = "Jafar";
console.log(`Hello, ${name}!`);