TC39: How we work, what we are working on, and how you can get involved (dotJS 2019)

@littledan
What TC39 is doing
and how you can help
Daniel Ehrenberg
Igalia, in partnership with Bloomberg
dotJS 2019

@littledan
About me
● Daniel Ehrenberg
● @littledan
● Live outside of Barcelona
● Work for Igalia
-- cooperative consultancy
● Mostly work on TC39

TC39 stages
● Stage 1: An idea under discussion
● Stage 2: We're doing this and have a ﬁrst draft
● Stage 3: Basically ﬁnal draft; ready to go
● Stage 4: 2+ implementations, tests ⇒ standard

@littledan
Stage 4 features
2+ implementations, tests ⇒ standard

What is BigInt?
➔ New primitive numeric type to do arbitrary length computations.
◆ New literal: 9128192832918293812823821n
◆ Operator overloading:
● 9007199254740991n + 2n === 9007199254740993n
➔ 64-bits TypedArray (BigInt64Array and BigUInt64Array).
➔ Standard Library to support type casts:
◆ BigInt() and Number() Constructors
➔ No implicit conversion between numbers and BigInt.

const x = 2 ** 53;
⇒ x === 9007199254740992
const y = x + 1;
⇒ y === 9007199254740992

const x = 2n ** 53n;
⇒ x === 9007199254740992n
const y = x + 1n;
⇒ y === 9007199254740993n

const x = 2n ** 53n;
⇒ x === 9007199254740992n
const y = x + 1n;
⇒ y === 9007199254740993n
nstands for BigInt

@littledan
Dynamic import():
Stage 4
Domenic Denicola

@littledan
Intl.RelativeTimeFormat:
Stage 4
Zibi Braniecki

Intl.RelativeTimeFormat
● Shipped in Chrome and Firefox
let rtf = new Intl.RelativeTimeFormat("en");
rtf.format(100, "day");
// "in 100 days"

@littledan
Optional chaining:
Stage 4
Daniel Rosenwasser
Claude Pache
Gabriel Isenberg
Dustin Savery

Optional
Property
Access
let x = foo?.bar;
// Equivalent to...
let x = (foo !== null && foo !== undefined) ?
foo.bar :
undefined;

@littledan
Nullish coalescing:
Stage 4
Daniel Rosenwasser
Gabriel Isenberg

Nullish
Coalescing
let x = foo() ?? bar();
// Equivalent to...
let tmp = foo();
let x = (tmp !== null && tmp !== undefined) ?
tmp :
bar();

@littledan
Stage 3 features
Basically ﬁnal draft; ready to go

@littledan
WeakRefs:
Stage 3
Sathya Gunasekaran
Till Schneidereit
Mark Miller
Dean Tribble

Read consistency
const w = new WeakRef(someObject);
...
if (w.deref()) {
w.deref().foo(); // w.deref() here can not fail
}

@littledan
Private ﬁelds and
methods:
Stage 3

Why?
● Private methods encapsulate
behavior
● You can access private ﬁelds inside
private methods
class Counter extends HTMLElement {
#x = 0;
connectedCallback() {
this.#render();
}
#render() {
this.textContent =
this.#x.toString();
}
}

# is the new _
for strong encapsulation

class PrivateCounter {
#x = 0;
}
let p = new PrivateCounter();
console.log(p.#x); // SyntaxError
class PublicCounter {
_x = 0;
}
let c = new PublicCounter();
console.log(c._x); // 0
Stage 3

@littledan
Stage 2 features
We're doing this and have a ﬁrst draft

@littledan
Decorators: Stage 2
Yehuda Katz
Ron Buckton

// Salesforce abstraction
import { api } from '@salesforce';
class InputAddress extends HTMLElement {
@api address = '';
}
Using decorators to track mutations and rehydrate
a web component when needed.
Syntax abstraction for attrs/props in Web Components
// Polymer abstraction
class XCustom extends PolymerElement {
@property({ type: String, reflect: true
})
address = '';
}
Example of using decorators to improve ergonomics.

@littledan
Temporal: Stage 2
Maggie Pint
Philipp Dunkel

@littledan
Stage 1 features
An idea under discussion

@littledan
Pipeline operator: Stage 1
Gilbert Garza
J.S. Choi
James DiGioia

library.js
export function doubleSay(str) {
return str + ", " + str;
}
export function capitalize(str) {
return str[0].toUpperCase() +
str.substring(1);
}
export function exclaim(str) {
return str + "!";
}
with-pipeline.js
import { doubleSay, capitalize, exclaim }
from "./library.js";
let result = "hello"
|> doubleSay
|> capitalize
|> exclaim;
// ===> "Hello, hello!"
ordinary.js
import { doubleSay, capitalize, exclaim }
from "./library.js";
let result =
exclaim(capitalize(doubleSay("hello")));
// ===> "Hello, hello!"

@littledan
Records and Tuples:
Stage 1
Robin Ricard
Richard Button

const marketData = #[
#{ ticker: "AAPL", lastPrice: 195.855 },
#{ ticker: "SPY", lastPrice: 286.53 },
];

@littledan
Operator overloading:
Stage 1

Vector overloading: Usage
// Usage example
import { Vector } from "./vector.mjs";
with operators from Vector;
new Vector([1, 2, 3]) + new Vector([4, 5, 6]) // ==> new Vector([5, 7, 9])
3 * new Vector([1, 2, 3]) // ==> new Vector([3, 6, 9])
new Vector([1, 2, 3]) == new Vector([1, 2, 3]) // ==> true
(new Vector([1, 2, 3]))[1] // ==> 2

@littledan
Stage 0 features
Not even really at a stage!

@littledan
BigDecimal: Stage 0
Andrew Paprocki

“Why are Numbers
broken in JS?”

Problem and solution (?)
// Number (binary 64-bit floating point)
js> 0.1 + 0.2
=> 0.30000000000000004
// BigDecimal (???)
js> 0.1d + 0.2d
=> 0.3d

Transparency, diversity and
inclusion in TC39

We have not been great in the past
Old process:
● Speciﬁcation: Big MS Word doc
● Communication: Meetings and es-discuss list
● Committee not nearly as diverse as JS programmers
● First-principles theorizing pushing out experience

TC39: How we work, what we are working on, and how you can get involved (dotJS 2019)

@littledan
Cultural evolution: The hardest part
● Newer values:
○ Accessibility to newer programmers
○ Integration into the existing JavaScript ecosystem
○ Incremental prototyping and iteration
○ Practicality over perfection (?)
● How to make tradeoffs?
Integrate with other value systems?
○ To be continued...

@littledan
Help wanted!
Any/all of the following appreciated

@littledan
Reﬁne proposals in
GitHub issues

@littledan
Write test262
conformance tests

@littledan
Implement tooling,
e.g., Babel, or
JS engines, e.g.,
browsers

@littledan
Prototype them in
your code and tell us
how it went

@littledan
Write documentation
and educational
materials

@littledan
Join Ecma and attend
TC39 meetings

@littledan
Conclusion
● Lots of things coming to JavaScript
● Stage process clarifies progress
● We could use your help!
● We are working on making a
friendly, open environment
● Daniel Ehrenberg
● @littledan
● https://tc39.es

@littledan
What really matters: Human and ecological needs
● The climate emergency:
Power structures are destroying the world
● Inclusive, collective action to save us!

@littledan
● The climate emergency:
Power structures are destroying the world
● Inclusive, collective action to save us!
like TC39 and free software are trying to build (???)

@littledan
● Let's solve important problems together
● JS is fun!

TC39: How we work, what we are working on, and how you can get involved (dotJS 2019)

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