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The full agenda including links to the slides and presentation materials can be found here. Full meeting notes will be published in roughly two weeks time. github.com/tc39/agendas...

agendas/2026/09.md at main · tc39/agendas

TC39 meeting agendas. Contribute to tc39/agendas development by creating an account on GitHub.

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The 116th meeting of @tc39.es was hosted by Sony Interactive Entertainment in Tokyo. Thanks to our hosts for again providing an excellent venue, facilities, refreshments, dedicated artwork(!), and an excellent events team 👍

A poster that says Sony Interactive Entertainment: Welcomes the 116th Meeting of TC39

A U-shaped table arrangement in the meeting room

180

ECMAScript excitement 😉 This week @tc39.es advanced these proposals 🎉 4️⃣ Dynamic Code Brand Checks 4️⃣ Iterator Chunking/Includes/Join 3️⃣ Thenable Curtailment 2️⃣.7️⃣ default in export * from "mod" 2️⃣.7️⃣ export defer 2️⃣.7️⃣ JSON.parse options 2️⃣ BigInt from Exponential 2️⃣ Composites 1️⃣ Pulling in AbortController

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Technically it's a shallow comparison. But if the children are all composites or primitives, that ends up being equivalent to a deep comparison. The comparison would fail if it hits two independent objects that have equivalent children. github.com/tc39/proposa...

GitHub - tc39/proposal-composites

Contribute to tc39/proposal-composites development by creating an account on GitHub.

020

Reposted by Rob Palmer

Seb ⚛️ ThisWeekInReact.com @sebastienlorber.com · 30/09/2026

Incredible news 🤯🎉

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ECMAScript excitement 😉 Congrats to @nicr.dev on advancing "Include default export in export * from" to Stage 2.7 at @tc39.es today 🎉 Today re-exporting the contents of another module omits the default export. It is believed this behavior change is web-compatible.

export * from 'mod';
export { default } from 'mod'; // redundant!

1332

ECMAScript excitement 😉 Congrats to @ashley-c.bsky.social from TechAtBloomberg on advancing the Composites proposal to Stage 2 at @tc39.es today 🎉 Composites are objects that are compared by value instead of identity. They are an evolution of Record & Tuple proposal.

const pos1 = Composite({ x: 1, y: 4 });
const pos2 = Composite({ x: 1, y: 4 });
pos1 === pos2; // true

const positions = new Set(); // the standard ES Set
positions.add(pos1);
positions.has(pos2); // true

913726

ECMAScript excitement 😉 Congrats to @nicr.dev on advancing `export defer` to Stage 2.7 at @tc39.es today 🎉 It is a performance feature that permits lazy evaluation of re-exported bindings. It is useful for reducing the cost of partially-used barrel files 👍

export defer { y } from "mod1";
export defer { z } from "mod2";

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ECMAScript excitement 😉 Congrats to Richard Gibson on advancing BigInt from Exponential to Stage 2 at @tc39.es today 🎉 🔶 BigInt("1e2") It allows a BigInt to be created from a number that includes an exponential component 👍

2194

WebStorm, a JetBrains IDE @webstorm.jetbrains.com · 25/09/2026

ECMAScript excitement 😉 Congrats to @peet.bsky.social from TechAtBloomberg advancing JSON.parse Options to Stage 2.7 at @TC39 today 🎉 There are two independent opt-ins. 🔶 deep freezing the entire object 🔶 non-array objects get a null prototype Names may change ⚠️

JSON.parse(
input: string,
reviverOrOptions?: Function | JsonParseOptions
): object
type JsonParseOptions = {
freeze?: boolean;
preferNullPrototype?: boolean
}

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Reposted by Rob Palmer

What if you could make one change to JavaScript? Absolutely anything you like. Justin Ridgewell tells us what he'd pick, straight from TC39's 114th meeting in Amsterdam. Watch the video 🎥 youtu.be/RHesVP6Seuo

youtu.be

If you had a superpower to make a single change to JavaScript – what would it be?

YouTube video by JetBrains

293

Reposted by Rob Palmer

Artem Zakharchenko @kettanaito.com · 29/09/2026

Now, that's a chunky proposal, indeed.

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Reposted by Rob Palmer

Seb ⚛️ ThisWeekInReact.com @sebastienlorber.com · 29/09/2026

👀 Great new JS feature Can be used for sliding window algorithms, such as a moving average Should also work on infinite streams, computing the moving average lazily

1181

Rob Palmer @robpalmer.bsky.social · 29/09/2026

ECMAScript excitement 😉 Congrats to @michael.ficarra.me on advancing the Iterator Chunking proposal to Stage 4 at @tc39.es today 🎉 It can make iterators that chunk & window content. [0,1,2,3].values().chunks(2); // [0,1], [2,3] [0,1,2,3].values().windows(2); // [0,1], [1,2], [2,3]

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Rob Palmer @robpalmer.bsky.social · 29/09/2026

ECMAScript excitement 😉 Congrats to @bakkot.com on advancing Iterator Join to Stage 4 at @tc39.es today 🎉 Iterator.prototype.join() turns an iterator directly into a single string (with an optional separator) just like Array.prototype.join() github.com/tc39/proposa...

GitHub - tc39/proposal-iterator-join: JS proposal for a means to concatenate the contents of an iterator into a string

JS proposal for a means to concatenate the contents of an iterator into a string - tc39/proposal-iterator-join

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Rob Palmer @robpalmer.bsky.social · 27/09/2026

More potential advancements: 2⃣ BigInt from exponential 2⃣ Composites 2⃣ Private Declarations 1⃣ Pulling in AbortController The full agenda is here: github.com/tc39/agendas...