What’s New in ES2024?

ECMAScript 2024 brings several exciting features that make JavaScript more powerful and developer-friendly. Let’s explore the most impactful additions.

Top-Level Await Improvements

ES2024 enhances top-level await with better error handling:

// Load configuration asynchronously
const config = await fetch('/api/config').then(r => r.json());

// Use it immediately in your module
export const apiUrl = config.apiUrl;

Array Grouping Methods

New methods make grouping array elements much easier:

const products = [
  { name: 'Laptop', category: 'Electronics' },
  { name: 'Chair', category: 'Furniture' },
  { name: 'Mouse', category: 'Electronics' },
];

// Group by category
const grouped = Object.groupBy(products, p => p.category);
// {
//   Electronics: [{ name: 'Laptop', ... }, { name: 'Mouse', ... }],
//   Furniture: [{ name: 'Chair', ... }]
// }

Map.groupBy for Map Results

const groupedMap = Map.groupBy(products, p => p.category);
// Returns a Map instead of a plain object

Promise.withResolvers()

A cleaner way to create promises with external resolvers:

// Before
let resolve, reject;
const promise = new Promise((res, rej) => {
  resolve = res;
  reject = rej;
});

// ES2024
const { promise, resolve, reject } = Promise.withResolvers();

// Use in event handlers
button.addEventListener('click', () => resolve('clicked'));

String.isWellFormed() and String.toWellFormed()

Handle Unicode strings more reliably:

const string = '\uD800'; // Lone surrogate

console.log(string.isWellFormed()); // false

const fixed = string.toWellFormed();
console.log(fixed.isWellFormed()); // true

ArrayBuffer and SharedArrayBuffer Improvements

Better control over binary data:

// Transfer ownership between workers
const buffer = new ArrayBuffer(1024);
worker.postMessage({ buffer }, [buffer]);
// Original buffer is now detached

// Check if buffer is detached
console.log(buffer.detached); // true

Temporal API Progress

While not fully finalized in ES2024, the Temporal API is making progress:

// Better date/time handling (when available)
import { Temporal } from '@js-temporal/polyfill';

const now = Temporal.Now.plainDateTimeISO();
const later = now.add({ hours: 2, minutes: 30 });

console.log(later.toString()); // 2024-11-10T14:30:00

Practical Examples

Data Processing Pipeline

const users = await fetch('/api/users').then(r => r.json());

// Group users by role
const byRole = Object.groupBy(users, user => user.role);

// Process each group
for (const [role, members] of Object.entries(byRole)) {
  console.log(`${role}: ${members.length} members`);
}

Promise Management

class AsyncQueue {
  constructor() {
    this.items = [];
    this.waiters = [];
  }

  enqueue(item) {
    if (this.waiters.length > 0) {
      const { resolve } = this.waiters.shift();
      resolve(item);
    } else {
      this.items.push(item);
    }
  }

  async dequeue() {
    if (this.items.length > 0) {
      return this.items.shift();
    }

    const { promise, resolve } = Promise.withResolvers();
    this.waiters.push({ resolve });
    return promise;
  }
}

Browser Support and Polyfills

Many ES2024 features are already supported in modern browsers. Check caniuse.com for specific feature support.

For older browsers, use:

  • Babel for syntax transformations
  • core-js for polyfills
  • @js-temporal/polyfill for Temporal API

Migration Tips

  1. Start small - Introduce new features gradually
  2. Test thoroughly - Ensure compatibility with your target browsers
  3. Use TypeScript - Many features have excellent TypeScript support
  4. Read documentation - MDN has comprehensive guides for each feature
  5. Stay updated - Follow TC39 proposals for upcoming features

Conclusion

ES2024 continues JavaScript’s evolution with practical features that solve real-world problems. From better array manipulation to improved promise handling, these additions make JavaScript more powerful and enjoyable to work with.

The key is understanding when to use each feature and how they fit into your existing codebase. Start experimenting with these features today, and your code will be cleaner and more maintainable tomorrow!