Nobody asks "How is JavaScript?"

From frontend developers to data scientists; from hobbyists to researchers, the
JavaScript programming language offers something to everyone. Still, while
everybody asks "what is JavaScript?" nobody asks "how is JavaScript?".

It might therefore be interesting to dig a bit deeper into this complex and
versatile programming language: Where is it going? How has it evolved over the
years? How does language design and evolution happen in the first place? What
are the rules put in place to ensure that it evolves in the right direction and
continue to serve its ever-evolving set of users and other stakeholders?

Join me in this overview of the TC39 standards committee, its processes and
initiatives as we learn just how much work goes into reshaping the most popular
programming language for the future.


(c) FOSDEM 2025
1 & 2 February 2025
https://fosdem.org/2025/schedule/event/fosdem-2025-4276-nobody-asks-how-is-javascript-/

1. Bienvenue
Welkom
Welcome

2. About Me
Ujjwal Sharma (ryzokuken)
from New Delhi, India
based out of A Coruña, Galiza
OSS zealot, open web maximalist
love dogs, (masochistic) videogames
work at Igalia

3. About
An open-source consultancy
A worker-owned cooperative
Extensive work across major open source projects and ecosystems
Linux kernel, userspace and multimedia
Major contributor in the web platform and browser projects
Compilers (JS engines, LLVM) and PL design (WASM, JS)
@ryzokuken

4. @ryzokuken

5. Everybody asks
"What is JavaScript?"
Nobody asks
"How is JavaScript?"
@ryzokuken

6. Did you know that JavaScript
is standardized?
@ryzokuken

7. What even is a
Standards Body?1
@ryzokuken

8. Do you remember ?????? ?
@ryzokuken

9. They’re venues for
unification & uniformization
●WHATWG
●W3C
●ISO
●ECMA
●Unicode
●…

@ryzokuken

10. TC39 is the
Technical Committee
that defines the
JavaScript language

@ryzokuken

11. Delegates
●Implementers (Apple, Google, Mozilla, Microsoft, …)
●Companies (Sony, Netflix, Bloomberg, …)
●Students and NPF (Universities, OpenJS F, …)

Invited Experts
●Subject matter experts
●Community representatives

Contributors, Editors, Reviewers & Community
Who participates?
@ryzokuken

12. Glossary …
❏ECMA
❏Technical Committee (TC39 , TC53, TC55)
❏TG2, TG3, TG4, TG5
❏ECMA-262 …
❏ECMAScript

@ryzokuken

13. How does
TC39 work? 2
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14. Consensus-based decisions
Diverse set of people in the committee
Implementers, Practitioners, Community Experts, Academics
Objections and concerns to satisfy everyone

No stakeholder has more power than others, concerns must be rational
@ryzokuken

15. STAGES
Steps where proposal evolves and receives
feedback

4 stages of maturity ← more on this later! ??????

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16. TASK GROUPS
TC39 charters sub-groups to work on focus areas:

?????? TG1: The core ECMAScript specification
?????? TG2: Internationalisation
?????? TG3: Security
?????? TG4: Sourcemaps ??????
?????? TG5: Research on Language Standardization ??????
@ryzokuken

17. Where

18. Where

19. When
6 Plenary Meetings a year
Online or In person
Focus Groups and Incubator
Calls
Monthly or Biweekly
TG2 / Editors / Outreach /
Proposals / Educators / Tools
Monthly or Biweekly
@ryzokuken

20. The Process
3
Stage-by-stage
2.7 &
@ryzokuken

21. STAGE 0 ??????
Strawperson
Just an Idea

Explainer, idea under discussion

Oversimplified proposal

23. STAGE 1
Describe the shape of a solution it’s an idea
under discussion

Proposal ??????
Devote time and have a “Champion”
Demos / Polyfills
Major changes

24. STAGE 1
Signals




Daniel Ehrenberg, Yehuda Katz, Jatin Ramanathan,
Shay Lewis, Kristen Hewell Garrett, Dominic
Gannaway, Preston Sego, Milo M, Rob Eisenberg

25. // A VanillaJS Counter
let counter = 0;
const setCounter = (value) => {
counter = value;
render();
};

const isEven = () => (counter & 1) == 0;
const parity = () => isEven() ? "even" : "odd";
const render = () => element.innerText = parity();

// Simulate external updates to counter...
setInterval(() => setCounter(counter + 1), 1000);

26. const counter = new Signal.State(0);
const isEven = new Signal.Computed(() => (counter.get() & 1) == 0);
const parity = new Signal.Computed(() => isEven.get() ? "even" : "odd");

27. STAGE 1
Decimal




Jesse Alama, Andrew Paprocki

28. 0.1 + 0.2 === 0.3

29. Sync Imports
Pattern Matching
Stabilize
Type Annotations
STAGE 1 ??????

Iterator Unique
Object pick/omit
...and around 80 others

30. STAGE 2 Draft??????
Describe syntactic and semantic details



Form spec language - Initial Spec Text

Semantics and API are covered - not completed

TC39 Expects that feature would be developed in future

Experimental

31. STAGE 2
Async Context




Andreu Botella, Chengzhong Wu, Justin Ridgewell

32. const asyncVar = new AsyncContext.Variable();

let snapshot
asyncVar.run("A", () => {
snapshot = new AsyncContext.Snapshot();
});

33. STAGE 2
Extractors




Ron Buckton

34. const Foo(y) = x; // instance-array destructuring
const Foo([y]) = x; // nested array destructuring
const Foo({y}) = x; // nested object destructuring
const [Foo(y)] = x; // nesting
const { z: Foo(y) } = x; // ..
const Foo(Bar(y)) = x; // ..
const X.Foo(y) = x; // qualified names (i.e., a.b.c)

Foo(y) = x; // instance-array destructuring
Foo([y]) = x; // nestedarray destructuring
Foo({y}) = x; // nested object destructuring
[Foo(y)] = x; // nesting
({ z: Foo(y) } = x); // ..
Foo(Bar(y)) = x; // ..
X.Foo(y) = x; // qualified names (i.e., a.b.c)

35. After Stage 2 comes...

Stage 2.7!
@ryzokuken

36. Why introduce a new stage?
High quality implementations need tests
...but tests can be expensive to write and costly to
iterate as the design changes

Test authors want to know when the design is stable
➡ Stage 2.7

Implementers want to know when the tests are ready
➡ Stage 3

??????
@ryzokuken

37. STAGE 2.7 Candidate??????
Approved in principle but still needs
feedback from testing and implementers


We have full spec text!

Reviewers and Editors have signed off the spec text

We will create test262 conformance tests

We might create spec-compliant implementations/polyfills

New!

38. test262.fyi
Test262(Github)
@ryzokuken

39. STAGE 2.7 Deferred Evaluation
Yulia Startsev, Nicolò Ribaudo

40. // This fetches but does NOT evaluate "mod"
import defer * as ns from "mod";


function rarelyUsed () {
// "mod" is lazily evaluated on first use of `ns`
console.log(ns.prop);
}

...
New!

41. STAGE 2.7 ShadowRealm






Dave Herman, Mark Miller, Caridy Patiño, Leo
Balter, Rick Waldron, Chengzhong Wu

42. const shadowRealm = new ShadowRealm();

// pluginFramework and pluginScript become available in the ShadowRealm
const [ init, ready ] = await Promise.all([
shadowRealm.importValue('./pluginFramework.js' , 'init'),
shadowRealm.importValue('./pluginScript.js', 'ready'),
]);

// The Plugin Script will execute within the ShadowRealm
init(ready);

43. STAGE 2.7 Math.sumPrecise






Kevin Gibbons

44. 1e20 + 0.1 + -1e20 === 0
Math.sumPrecise([1e20, 0.1, -1e20]) === 0.1

45. STAGE 3
Recommended for
implementation??????
Implementation and validation phase
(feedback from implementers, web-compatibility)


Tests have been created for test262

We will only change things if implementation reveals new information

Engines will begin implementing

Browsers may start shipping with or without a flag

46. STAGE 3 Temporal
Philipp Dunkel , Maggie Johnson-Pint,
Matt Johnson-Pint, Brian Terlson,
Shane Carr, Ujjwal Sharma, Philip Chimento,
Jason Williams, Justin Grant

48. const yearMonth = Temporal.PlainYearMonth.from({ year: 2020, month: 10 });


yearMonth.toString() // => 2020-10
yearMonth.daysInMonth; // => 31
yearMonth.daysInYear; // => 366


const monthDay = Temporal.PlainMonthDay.from({ month: 7, day: 14 });
const date = monthDay.toPlainDate({ year: 2030 });

date.dayOfWeek; // => 7
date.dayOfYear; // => 195
date.daysInMonth; // => 31
date.daysInYear; // => 365
date.inLeapYear; // => false

49. let calcDate = Temporal.Now.plainDateISO(); // => 2021-11-29

calcDate.add({ days : 15 }); // => 2021-12-14

calcDate.subtract({ days : 15 }); // => 2021-11-14

calcDate.equals(calcDate); // => true
calcDate.equals(calcDate.add({ days : 2})); // => false

50. const time = Temporal.Instant.fromEpochSeconds(new Date);

Temporal.TimeZone.from('Europe/Berlin').getOffsetStringFor(time);
// => +01:00

Temporal.TimeZone.from('America/Vancouver').getOffsetStringFor(time)
// => -08:00

Temporal.TimeZone.from('Europe/Moscow').getOffsetStringFor(time);
// => +03:00

51. STAGE 3 Decorators
Kristen Hewell Garrett

52. function bound(value, { name, addInitializer }) {
addInitializer(function () {
this[name] = this[name].bind(this);
});
}

class C {
message = "hello!";
@bound
m() {
console.log(this.message);
}
}

let { m } = new C();
m(); // hello!

53. STAGE 4 Finished??????
About to be include in the upcoming edition
of ECMAScript®





We have two implementations that pass the acceptance tests

We have real-life experience of shipping the feature

We have merged the feature into the Spec

It might not yet be shipping in all mainstream engines

The feature will be included in the next yearly edition, e.g. ES2024

54. STAGE 4 ArrayBuffer transfer
Shu-yu Guo, Jordan Harband, Yagiz Nizipli

55. function validateAndWriteSafeAndFast (arrayBuffer) {
// Transfer to take ownership, which implementations can choose to
// implement as a zero-copy move.
const owned = arrayBuffer.transfer();

// arrayBuffer is detached after this point.
assert(arrayBuffer.detached);

await validate(owned);
await fs.writeFile("data.bin", owned);
}

56. STAGE 4 Set Methods
Kevin Gibbons

57. let odds = new Set([1, 3, 5, 7, 9, 11, 13]);
let primes = new Set([2, 3, 5, 7, 11, 13]);

let oddPrimes = primes.intersection(odds);
// Set { 3, 5, 7, 11, 13 }

let evenPrimes = primes.difference(odds);
// Set { 2 }

58. Array Grouping
Atomics.waitAsync
Promise.withResolvers
Well-Formed Unicode Strings
RegExp v flag
+ set notation
+ properties of strings
Resizable & growable ArrayBuffers
STAGE 4 ??????
ArrayBuffer transfer

59. ECMAScript 2025


ES.next


Next June

esbuild

60. Collaboration & Help
Get involved!4
@ryzokuken

61. Write test262 conformance tests

Refine proposals in GitHub issues

Write documentation and educational materials

Provide feedback on GitHub



??????
??????
??????
??????
@ryzokuken

62. ??????
Merci
Bedankt
Thanks