Babel progress on ECMAScript proposals

Official TC39 Proposals Repo

Proposals

For the official list, check the TC39 repo. This list only contains all proposals higher than Stage 0 that are compilable by Babel. (If Stage 4, it will be in preset-env)

Implemented

Rest/Spread Properties

TC39 Champion: Sebastian Markbage
Preset: babel-preset-stage-3
Plugin: babel-plugin-transform-object-rest-spread
Babylon Label: Spec: Object Rest/Spread

// Rest properties
let { x, y, ...z } = { x: 1, y: 2, a: 3, b: 4 };
console.log(x); // 1
console.log(y); // 2
console.log(z); // { a: 3, b: 4 }

// Spread properties
let n = { x, y, ...z };
console.log(n); // { x: 1, y: 2, a: 3, b: 4 }

Asynchronous Iteration

TC39 Champion: Domenic Denicola
Preset: babel-preset-stage-3
Plugin: babel-plugin-transform-async-generator-functions

async function* agf() {
  await 1;
  yield 2;
}

async function f() {
  for await (let x of y) {
    g(x);
  }
}

Dynamic Import

TC39 Champion: Domenic Denicola
Preset: babel-preset-stage-3
Plugins: babel-plugin-syntax-dynamic-import

Webpack 1: https://github.com/airbnb/babel-plugin-dynamic-import-webpack
Webpack 2: supports this by default (just needs Babel to parse)
Node: https://www.npmjs.com/package/babel-plugin-dynamic-import-node

import('test-module').then(() => (
  import('test-module-2');
));

RegExp Unicode Property Escapes

TC39 Champion: Brian Terlson, Daniel Ehrenberg, Mathias Bynens
Preset: babel-preset-stage-3
Plugins: babel-plugin-transform-unicode-property-regex

const a = /^\p{Decimal_Number}+$/u;
const b = /\p{Script_Extensions=Greek}/u;

RegExp Named Capture Groups

TC39 Champion: Daniel Ehrenberg, Brian Terlson
Preset: N/A
Plugins: babel-plugin-transform-modern-regexp (with namedCapturingGroups flag)

let re = /(?<year>\d{4})-(?<month>\d{2})-(?<day>\d{2})/u;

let result = re.exec('2015-01-02');
// result.groups.year === '2015';
// result.groups.month === '01';
// result.groups.day === '02';

// result[0] === '2015-01-02';
// result[1] === '2015';
// result[2] === '01';
// result[3] === '02';

Regexp DotAll Flag

TC39 Champion: Daniel Ehrenberg, Jeff Morrison Preset: N/A
Plugins: babel-plugin-transform-dotall-regex, babel-plugin-transform-modern-regexp (with dotAll flag)

/./s; // /[\0-\uFFFF]/;

Class Fields

TC39 Champion: Daniel Ehrenberg, Jeff Morrison

Stage 2

Preset: WIP
Plugins: WIP
First Pull Request: babel/babylon#608 by @diervo
Babylon Label: Spec: Class Fields

Stage 1

Preset: babel-preset-stage-1
Plugins: babel-plugin-transform-class-properties

class Bork {
  instanceProperty = "bork";
  boundFunction = () => {
    return this.instanceProperty;
  }

  static staticProperty = "babelIsCool";
  static staticFunction = function() {
    return Bork.staticProperty;
  }
}

Class and Property Decorators

TC39 Champion: Yehuda Katz and Brian Terlson

Stage 2

Preset: WIP
Plugins: WIP

Stage 1

Preset: babel-preset-stage-1
Plugins: babel-plugin-transform-decorators, babel-plugin-transform-decorators-legacy
First Pull Request: babel/babylon#587 by @peey
Babylon Label: Spec: Decorators

@frozen class Foo {
  @configurable(false) @enumerable(true) method() {}
}
function frozen(constructor, parent, elements) {
  return {
    constructor,
    elements,
    finisher(constructor) {
      Object.freeze(constructor.prototype)
      Object.freeze(constructor)
    }
  }
}
function configurable(configurable) {
  return decorator;
  function decorator(previousDescriptor) {
    return {
      ...previousDescriptor,
      descriptor: {
        ...previousDescriptor.descriptor,
        configurable
      }
    }
  }
}
function enumerable(enumerable) {
  return decorator;
  function decorator(previousDescriptor) {
    return {
      ...previousDescriptor,
      descriptor: {
        ...previousDescriptor.descriptor,
        enumerable
      }
    }
  }
}

Export Extensions

This proposal was split into 2:
https://github.com/tc39/proposal-export-ns-from
https://github.com/tc39/ecmascript-export-default-from

TC39 Champion: Lee Byron
Preset: babel-preset-stage-1
Plugins: babel-plugin-transform-export-extensions

export * as ns from 'mod'; // export-ns-from
export v from 'mod'; // export default from

Optional Chaining

TC39 Champion: Gabriel Isenberg
Preset: babel-preset-stage-1
Plugins: babel-plugin-transform-optional-chaining

obj?.prop       // optional property access
obj?.[expr]     // optional property access
func?.(...args) // optional function or method call

a?.b = 42; // a == null ? undefined : a.b = 42;

do Expressions

TC39 Champion: Dave Herman
Preset: babel-preset-stage-1
Plugins: babel-plugin-transform-do-expressions

let a = do {
  if (x > 10) {
    'big';
  } else {
    'small';
  }
};

// let a = x > 10 ? 'big' : 'small';

Numeric Separator

TC39 Champion: Sam Goto
Preset: babel-preset-stage-1
Plugins: babel-plugin-transform-numeric-separator
First Pull Request: babel/babylon#541 by @rwaldron
Babylon Label: Spec: Numeric Separator

// Decimal Literals
let budget = 1_000_000_000_000;
// Binary Literals
let nibbles = 0b1010_0001_1000_0101;
// Hex Literal
let message = 0xA0_B0_C0;

Function Bind

TC39 Champion: Brian Terlson & Matthew Podwysocki
Preset: babel-preset-stage-0
Plugins: babel-plugin-transform-function-bind

obj::func
// is equivalent to:
func.bind(obj)

obj::func(val)
// is equivalent to:
func.call(obj, val)

::obj.func(val)
// is equivalent to:
func.call(obj, val)

function.sent

TC39 Champion: Allen Wirfs-Brock
Preset: babel-preset-stage-2
Plugins: babel-plugin-transform-function-sent

function* generator() {
  console.log("Sent", function.sent);
  console.log("Yield", yield);
}

const iterator = generator();
iterator.next(1); // Logs "Sent 1"
iterator.next(2); // Logs "Yield 2"

Parser Only

BigInt

TC39 Champion: Daniel Ehrenberg
Preset: WIP
Plugins: WIP
First Pull Request: babel/babylon#588 by @wdhorton
Babylon Label: Spec: BigInt

1n // integer
0b101n // binary
0xFF123n // hex
0o16432n // octal
9223372036854775807n // larger than floating

// Invalid
1.0n // no decimals
2e9n // no exponential notation
016n // no old octal

import.meta

TC39 Champion: Domenic Denicola
Preset: babel-preset-stage-2
Plugins: babel-plugin-syntax-import-meta
First Pull Request: babel/babylon#544 by @jkrems
Babylon Label: Spec: import.meta

import.meta.url;
import.meta.scriptElement.dataset.size;

Not Implemented

Pattern Matching

TC39 Champion: Brian Terlson (Microsoft, @bterlson), Sebastian Markbåge (Facebook, @sebmarkbage)
Preset: WIP
Plugins: WIP
Babylon Label: Spec: pattern matching
First Pull Request: babel/babylon#635 by @krzkaczor

let length = vector => match (vector) {
    { x, y, z }: Math.sqrt(x ** 2 + y ** 2 + z ** 2),
    { x, y }:   Math.sqrt(x ** 2 + y ** 2),
    [...]:      vector.length,
    else: {
        throw new Error("Unknown vector type");
    }
}

let isVerbose = config => match (config) {
    { output: { verbose: true } }: true,
    else: false
}

let outOfBoundsPoint = p => match (p) {
    { x > 100, y }: true,
    { x, y > 100 }: true,
    else: false
}

Generator Arrow Functions

TC39 Champion: Brendan Eich, Domenic Denicola
Preset: N/A
Plugins: N/A

()=>*{}

FAQ

When does Babel implement new features?

Babel will accept any PR for a proposal that is intended to go through the TC39 Proposal Process. This just means that we could implement and release a proposal starting at Stage 0. However this doesn't mean that we will implement it ourselves, but that we will work with both TC39 Champions and the community to get an implementation in. (And sometimes we have to wait for Summer of Code for that to happen).

It's our intention (and one of our main goals) as a project to help TC39 get feedback from the community through using the new syntax in their codebases. There is however a balance between supporting new proposals and informing users that any proposal is still just a proposal and subject to change. In order to move the community forward, we will continously make changes to adhere to the spec as patches. If bigger changes require a major version, we will deprecate older versions of plugins, document those changes, and see if we can automate the upgrade via a codemod. This way everyone is moving towards Stage 4 and closer to what will be in the spec if the proposal makes it to the end.

This means we will also include proposals in this repo that haven't been presented to the committee yet if they are concrete enough and someone on TC39 is planning on presenting it (and marked appropriately).