JS: ECMAScript 2026

getOrInsert , getOrInsertComputed for map and weak map

new methods

• Map.prototype.getOrInsert
• Map.prototype.getOrInsertComputed

also in weakmap.

• WeakMap.prototype.getOrInsert
• WeakMap.prototype.getOrInsertComputed

• JS: Map.prototype.getOrInsert
• JS: Map.prototype.getOrInsertComputed
• JS: WeakMap

(ai answer)

Key New Features

Array.fromAsync

Creates an array from an async iterable (e.g., streams, paginated APIs).◆ const arr = await Array.fromAsync(asyncIterable);

Uint8Array Base64 & Hex methods

Native toBase64(), fromBase64(), hex conversions (and similar).◆ No more btoa/atob hacks or third-party libs for binary data.

Error.isError

Reliable way to check if something is truly an Error (works across realms/iframes/workers).◆ Fixes instanceof Error pitfalls.

JSON improvements

Reviver access to source text in JSON.parse; JSON.rawJSON for better stringify control.◆ Safer handling of large numbers and precise JSON round-tripping.

Other Notable Mentions (Depending on Exact Cutoff)

Some sources also reference features that reached Stage 4 around the same time or were expected:

• Iterator helpers (.map(), .filter(), .take(), etc. on iterators)
• Promise.try()
• RegExp.escape()
• Float16 support (Float16Array, Math.f16round)
• In some reports: progress toward Temporal (modern Date replacement) and explicit resource management (using / await using)

Reference

• https://tc39.es/ecma262/2026/multipage/