Do you ever wonder how ECMAScript evolves and why it's available almost everywhere? We're going to take you through how TC39 (the technical committee responsible for ECMAScript) works, how to participate and contribute, as well as how an idea can make its way into the language, all step by step. We'll also provide a sneak peek and engage in a debate about some recent and interesting proposals in various stages of development. (c) JetBrains JavaScript Day 2023

1. From the proposal to
ECMAScript
Step by step
@romulocintra

2. Hello 👋👋👋👋👋
0 #JetBrains
JS Day Folks

3. I’m Romulo Cintra
∎ Doing Web Stuff -
● Browsers and Client-side Web Technologies
○ Webkit , Wolvic, WPE , JSC , Chromium, V8 ,
SpiderMonkey,…
● Standards
○ WASM , TC39 , Unicode , W3C …
● Compilers, Graphics, Multimedia, Device
Drivers

4. What’s Standards
BODY and TC39 ?
1

5. Do you remember 🧀?

6. @romulocintra
They’re Avenues for
unification & uniformization
● WHATWG
● W3C
● ISO
● ECMA
● Unicode
● …

7. @romulocintra
Marvel Studios

8. @romulocintra
TC39 is the
Technical committee
that defines the
JavaScript language

9. Glossary …
❏ ECMA
❏ ECMA-262 …
❏ ECMAScript
❏ JavaScript
❏ TC-XX (TC39 , TC45)
@romulocintra

10. How
TC39 works?
2

11. @romulocintra
Consensus-based decision
Diverse set of people in the committee
Implementers , Practitioners, Community Experts
Objections and concerns to satisfy everyone’s
No stakeholder kept over another and , Backing rationales

12. @romulocintra
STAGES
Steps where proposal evolves and receives
feedback
1 + 4 Stages

13. When & How
4-8 Plenary
Meetings a year
Online or In person
Focus Groups and Incubator
Calls
Monthly or Biweekly
TG2/TG4 / Editors / Outreach /
Proposals / Educators / Tools
Monthly or Biweekly

14. The Process
3 Stage-by-stage

15. @romulocintra
STAGE 0 💡
Strawperson
Just an Idea
Explainer, Idea under discussion,
Strawperson Proposal

16. @romulocintra

17. @romulocintra
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

18. STAGE 1
Types Annotations
Daniel Rossenwaver, Rob Palmer,
Romulo Cintra

21. STAGE 1
Pattern Matching
Daniel Rosenwasser, Jack Works, Jordan Harband,
Mark Cohen, Ross Kirsling, Tab Atkins-Bittner,
Yulia Startsev

22. const res = await fetch(jsonService);
match (res) {
when ({ status: 200, headers: { 'Content-Length': s } }):
console.log(`size is ${s}`);
when ({ status: 404 }):
console.log('JSON not found');
when ({ status }) if (status >= 400): do {
throw new RequestError(res);
}
};

23. @romulocintra
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

24. @romulocintra

25. STAGE 2
Deferring Module
Evaluation
Yulia Startsev, Nicolò Ribaudo

26. // Eagerly load&link mod and its dependencies
import defer * as ns from "mod";
function rarelyUsed() {
// Later, ns.someValue triggers the evaluation of mod
doSomethingWith(ns.someValue);
}

27. @romulocintra
STAGE 3 Candidate ��
Refinement phase(Feedback from
implementers and users), almost ready to go
Completed Spec Text
Have Reviewers and Editors Signed off the spec
Coverage on Test262
Spec Compliant
Some browser might implement under a flag

28. test262.fyi
Test262(Github)

29. STAGE 3 Intl.DurationFormat
Younies Mahmoud, Ujjwal Sharma

30. const duration = { seconds: 12, milliseconds: 345, microseconds: 600 } ;
new Intl.DurationFormat('en', { style: "digital", fractionalDigits: 2 }).format(duration);
// "0:00:12.35"
new Intl.DurationFormat('en', { seconds: "numeric", fractionalDigits: 2
}).format(duration);
// "12.35"
> new Intl.DurationFormat('en', { seconds: "numeric", fractionalDigits: 5
}).format(duration);
// "12.34560"
> new Intl.DurationFormat('en', { seconds: "numeric"}).format(duration);
// "12.3456"

31. new Intl.DurationFormat("fr-FR", { style: "long" }).format({
hours: 1,
minutes: 46,
seconds: 40,
});
// => "1 heure, 46 minutes et 40 secondes"

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

33. 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

34. 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

35. 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

36. @romulocintra
STAGE 4 Finished ��
About to be include in the upcoming edition
of ECMAScript®
Merged into the Spec text
Two implementations that passes acceptance tests
Will be included on the upcoming Spec
Shipping

37. STAGE 4 Change Array By Copy
Robin Ricard
Ashley Claymore

38. const original = [1, 2, 3, 4];
const reversed = original.toReversed();
// -> [ 4, 3, 2, 1 ]
const sorted = original.toSorted();
// -> [ 1, 2, 3, 4 ]
const spliced = original.toSpliced(0, 4, 2 , 3, 5 );
// -> [ 2, 3, 5]
const withThree = original.with(3, 10);
original.with(2, 3);
// -> [1, 2, 3, 10]

39. Error: .cause Symbols as
WeakMap keys
Top-level await
Array find from last
Search : T39 finished-proposals.md

40. ECMAScript 2024
ES.next
June 2024

41. Collaboration & Help
Get involved !!!
4

42. @romulocintra
Write test262 conformance tests
Refine proposals in GitHub issues
Write documentation and
educational materials
Provide feedback on GitHub
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43. Muchas Gracias
Thanks
Obrigado
Спасибо
@romulocintra