ES6 JavaScript in 2026: What Actually Matters When You Maintain Real Code

Most “ES6 guide” posts you find are from 2016 and stop at let and arrow functions. That’s not useful if you’re staring at a 4,000-line file someone else wrote. This is the version I wish existed when I started cleaning up older JavaScript codebases for clients. It covers the ES6+ features that matter in 2026, the ones that quietly break things, and what to reach for instead of the habits you picked up years ago.

ES6 is not new anymore. Treat it as the baseline.

ES2015 (what everyone calls ES6) shipped a decade ago. By 2026 every browser you care about supports it natively, and so does Node. If you’re still transpiling for IE11, that’s a separate, sad conversation. The practical reality: you can write ES6+ directly and ship it. The interesting question isn’t “what is ES6” but “which parts of it are load-bearing in code I have to maintain.”

The features you actually use every day

• const and let instead of var. Use const by default. Reach for let only when you reassign.
• Arrow functions, but be careful about this. They don’t bind their own this, which is either exactly what you want or the source of a bug.
• Template literals. Stop concatenating strings with +.
• Destructuring. Pulling values out of objects and arrays without five lines of setup.
• Modules (import/export). This replaced the old script-tag-and-global-variable approach.
• Promises, and by extension async/await (technically ES2017, but nobody separates them in practice).

Destructuring and defaults, done right

This is where I see the most subtle bugs in inherited code. Destructuring is great, but the default value only kicks in for undefined, not null.

function createUser({ name, role = 'viewer', tags = [] } = {}) {
 return { name, role, tags };
}

createUser({ name: 'Dana' });
// { name: 'Dana', role: 'viewer', tags: [] }

createUser({ name: 'Dana', role: null });
// { name: 'Dana', role: null, tags: [] } <-- default did NOT apply

That trailing = {} matters too. Without it, calling createUser() with no argument throws, because you can't destructure undefined. I've fixed that exact bug more than once.

Optional chaining and nullish coalescing

These are ES2020, not ES6, but they're the reason you can delete half the defensive code in older files. Use them.

// Old, painful
const city = user && user.address && user.address.city ? user.address.city : 'Unknown';

// Now
const city = user?.address?.city ?? 'Unknown';

The key difference between ?? and ||: ?? only falls back on null or undefined. So 0 || 'default' gives you 'default', which is probably a bug, while 0 ?? 'default' correctly gives you 0. If you're handling counts, prices, or anything where zero is valid, use ??.

Async code without the callback pyramid

Promises fixed callback hell, and async/await made it readable. The mistake I still see: awaiting things in a loop when they could run in parallel.

// Slow: waits for each request one at a time
async function loadAll(ids) {
 const results = [];
 for (const id of ids) {
 results.push(await fetchItem(id));
 }
 return results;
}

// Fast: fires them together
async function loadAll(ids) {
 return Promise.all(ids.map((id) => fetchItem(id)));
}

One caveat with Promise.all: if one request rejects, the whole thing rejects and you lose the others. If you want partial results, use Promise.allSettled and check each result's status.

Modules and the "type": "module" switch

If you're working in Node, the module situation is finally boring in 2026. You set "type": "module" in package.json and use import/export like you would in the browser. No more require unless you're stuck on a CommonJS dependency.

// package.json
{
 "type": "module"
}

// then in your code
import { readFile } from 'node:fs/promises';

const data = await readFile('./config.json', 'utf8');

Top-level await works in ES modules, which cleans up a lot of startup boilerplate.

What to skip or replace

Some ES6-era habits aged badly. A few I'd leave behind:

• Loose var. Function scoping and hoisting surprises aren't worth it. Use const.
• Classes for everything. ES6 classes are fine, but a lot of code that reached for them would be cleaner as plain functions and objects. Don't force it.
• Spread for deep copies. { ...obj } is a shallow copy. Nested objects are still shared references. Use structuredClone() for a real deep copy.

const original = { user: { name: 'Dana' } };
const shallow = { ...original };
shallow.user.name = 'Sam';
console.log(original.user.name); // 'Sam' <-- you changed the original too

const deep = structuredClone(original);
deep.user.name = 'Alex';
console.log(original.user.name); // 'Sam' <-- safe

Do you even need a build step in 2026?

Often, no. Modern browsers handle ES modules, async/await, optional chaining, and most of what you'd write. If your project is a straightforward site or a small app, you can drop the bundler and ship native modules. That said, bundlers still earn their keep when you have hundreds of modules, need tree-shaking, or want a single optimized file for performance. The honest answer is: it depends on the project, and anyone who tells you "always bundle" or "never bundle" is selling something.

For the smaller sites and business apps I build, I usually start without a bundler and only add one when the file count justifies it. If you're weighing that tradeoff for a project, it's the kind of thing worth talking through as part of custom web development rather than guessing.

Quick reference: the features worth memorizing

• const / let over var
• Arrow functions (watch this)
• Template literals
• Destructuring with correct defaults
• import / export
• async / await plus Promise.all and Promise.allSettled
• Optional chaining ?. and nullish coalescing ??
• structuredClone() for deep copies

None of this is exotic. That's the point. ES6 and the versions after it are just how JavaScript works now, and knowing which parts to lean on (and which old habits to drop) is most of the difference between code you can maintain and code you dread opening.

FAQ

Is ES6 still worth learning in 2026?

Yes, but not as a separate topic. It's the baseline for all modern JavaScript. Learn current syntax as one thing rather than treating ES6 as a milestone.

Do I still need Babel or a bundler?

Usually not for browser support alone. You might still want a bundler for tree-shaking and performance on large projects, but you can ship native ES modules for most sites.

What's the biggest mistake people make with ES6 code?

Using || where ?? belongs (it breaks on 0 and empty strings), and assuming spread syntax does a deep copy when it doesn't.