What's new in ECMAScript 2026 (and usable today)

JavaScript Weekly issue 793 covers the approval of the ECMAScript 2026 spec and highlights several features that are already usable today. The issue also packs in a dense set of ecosystem updates worth a ConfigDeck-lens look.

What’s actually new

The ECMAScript 2026 spec — 876 pages — was approved last week. Pawel Grzybek’s linked roundup covers the main additions, including Array.fromAsync and native Uint8Array Base64/Hex conversion. Nearly everything is already shipping in browsers and runtimes, with Math.sumPrecise in Node being the noted exception. Beyond the spec itself, this issue surfaces several releases with config implications: webpack-dev-server 6.0 upgrades to Express 5 and native ESM, Cloudflare’s vinext 1.0 Beta reimplements Next.js’s API surface as a Vite plugin, and shadcn/ui has switched its default component library from Radix to Base UI (Radix remains supported but Base UI is now recommended for new projects). There’s also a TC39 proposal to standardize a code property on Error, formalizing what’s long been a de-facto Node convention.

What it means for your config

The webpack-dev-server 6.0 upgrade to Express 5 and native ESM is the item most likely to touch your config files directly. If you’re running a devServer block in your webpack config with Express 4 middleware or CommonJS-only plugins, expect breakage — though the source doesn’t detail specific migration steps, so check the release notes before upgrading.

The vinext beta is interesting for teams currently juggling next.config.js alongside Cloudflare Workers config. It reimplements Next.js’s API surface on Vite, which means your build config story could simplify if you’re deploying to Cloudflare — but it’s a beta, so treat it accordingly.

For shadcn/ui users: switching from Radix to Base UI as the default doesn’t force an immediate migration — Radix is still supported. But new projects scaffolded with shadcn/ui will pull in Base UI, so your component-level dependencies and any related config (bundler aliases, tree-shaking settings) may shift over time.

The ECMAScript 2026 features themselves don’t require config changes. They’re spec-level additions already in engines, so your tsconfig.json target or ESLint ecmaVersion settings shouldn’t need adjustment to use them — though if you’re still targeting older environments via Babel, you may want to verify plugin coverage for Array.fromAsync and the Uint8Array methods.

Recommended next step

If you’re on webpack-dev-server 5.x, read the 6.0 changelog before bumping — the Express 5 and ESM shift is the kind of thing that breaks silently in CI. For the ECMAScript 2026 features, Grzybek’s original roundup includes examples for each addition; skim it to see which ones you can drop polyfills for today. And if you’re starting a new shadcn/ui project, go with Base UI as the default unless you have specific Radix dependencies — fighting upstream defaults is never worth the maintenance cost.

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Read the full announcement on JavaScript Weekly → What’s new in ECMAScript 2026 (and usable today)