v6.16.0 (2016-09-28)

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Babel 6.16: Happy 2nd Birthday 🎂 !

Blog post here: http://babeljs.io/blog/2016/09/28/6.16.0

👓 Spec Compliancy

• babel-core, babel-generator, babel-helper-remap-async-to-generator, babel-helpers, babel-plugin-transform-async-generator-functions, babel-types, babel-preset-stage-2, ...
  • #3473 via #4576 Implement support for async generator functions and for-await statements. (@zenparsing)

This change implements the async iteration proposal, currently at stage 2 (and pushing to stage 3 at the current TC-39 meeting). It includes the following features:

• Transforms async generator functions (async function* g() { }) to wrapped generator functions, similar to the current async-to-generator transform.

async function* agf() {
  this;
  await 1;
  yield 2;
  return 3;
}

• Transforms for-await statements into for loops containing yield expressions.

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

Example Usage

async function* genAnswers() {
  var stream = [ Promise.resolve(4), Promise.resolve(9), Promise.resolve(12) ];
  var total = 0;
  for await (let val of stream) {
    total += await val;
    yield total;
  }
}

function forEach(ai, fn) {
  return ai.next().then(function (r) {
    if (!r.done) {
      fn(r);
      return forEach(ai, fn);
    }
  });
}

var output = 0;
return forEach(genAnswers(), function(val) { output += val.value })
.then(function () {
  assert.equal(output, 42);
});

• babel-core, babel-generator, babel-plugin-transform-class-properties, babel-template, babel-traverse, babel-types
  • #4500 Computed class properties. (@motiz88)

Parser support was added in babylon@6.11.0 with babel/babylon#121

// Example
class Foo {
  [x]
  ['y']
}

class Bar {
  [p]
  [m] () {}
}

• babel-generator
  • #3702 flow plugin: generate exact object type annotations. (@bhosmer)

Parser support was added in babylon@6.10.0 with babel/babylon#104

// Example
var a : {| x: number, y: string |} = { x: 0, y: 'foo' };

🚀 New Feature

• babel-core, babel-generator
  • #3561 babel-core: add options for different parser/generator. (@hzoo)

Babel will now also take the options: parserOpts and generatorOpts (as objects).

parserOpts will pass all properties down to the default babylon parser. You can also pass a parser option to substitute for a different parser.

This will allow passing down any of babylon's options:

{
  "parserOpts": {
    "allowImportExportEverywhere": true,
    "allowReturnOutsideFunction": true,
    "sourceType": "module",
    "plugins": ["flow"]
  }
}

Another use case (the main reason for doing this), is to be able to use recast with Babel.

{
  "parserOpts": {
    "parser": "recast"
  },
  "generatorOpts": {
    "generator": "recast"
  }
}

• babel-core
  • #4542 Add support for preset organization shortcuts. (@nkt)

{
  presets: ["@org/babel-preset-name"], // actual package
  presets: ["@org/name"] // shorthand name
}

• babel-plugin-transform-object-rest-spread
  • #4491 object rest spread useBuiltIns option. (@hzoo)

useBuiltIns - Do not use Babel's helper's and just transform to use the built-in method (Disabled by default).

{
  "plugins": [
    ["transform-object-rest-spread", { "useBuiltIns": true }]
  ]
}

// source
z = { x, ...y };
// compiled
z = Object.assign({ x }, y);

• babel-code-frame
  • #4561 babel-code-frame: add options for linesBefore, linesAfter. (@hzoo)

babel-code-frame is a standalone package that we use in Babel when reporting errors.

Now there is an option to specify the number of lines above and below the error

  1 | class Foo {
> 2 |   constructor()
    |                ^
  3 | }

• babel-core, babel-preset-es2015, babel-preset-es2016, babel-preset-es2017, babel-preset-latest, babel-preset-react, babel-preset-stage-0, babel-preset-stage-1, babel-preset-stage-2, babel-preset-stage-3
  • #3695 via #4566 Allow presets to be ES6 default exports (@johanssj)

We previously made presets with commonjs exports

module.exports = {
  plugins: [
    require("babel-plugin-syntax-trailing-function-commas")
  ]
};

Now you can use export default as well

import transformExponentiationOperator from "babel-plugin-transform-exponentiation-operator";
export default {
  plugins: [
    transformExponentiationOperator
  ]
};

🐛 Bug Fix

• babel-helpers, babel-plugin-transform-es2015-typeof-symbol
  • #3686 Fix typeof Symbol.prototype. (@brainlock)

// `typeof Symbol.prototype` should be 'object'
typeof Symbol.prototype === 'object'

• babel-cli
  • #3456 Use the real sourcemap API and handle input sourcemaps - Fixes #7259. (@loganfsmyth)
  • #4507 Only set options in cli if different from default. (@danez)

Fix an issue with defaults not being overidden. This was causing options like comments: false not to work correctly.

• #4508 Support custom ports for V8 --inspect. (@andykant)
• #4562 Fixes #2299: Prevent REPL from printing implicit 'use strict'. (@hzoo)
  • babel-plugin-transform-es2015-function-name, babel-traverse
• #4524 Fix default export with arrows and function naming. (@danharper)

// wasn't exporting correctly before
export default ({ onClick }) => {
  return <div onClick={() => onClick()}></div>;
}

• babel-plugin-transform-es2015-modules-commonjs
  • #4511 Fix UpdateExpression handling in es2015-modules-commonjs, resolve #4462. (@motiz88)
  • #4518 fix default exported classes without a name. (@danez)

export default class {};
// wasn't correctly transforming to
exports["default"] = class {}
// with the es3-tranforms

• babel-plugin-transform-flow-strip-types, babel-types
  • #4521 Fix striping of typeParameters from arrow functions. (@danez)

// <X> wasn't stripped out
const find = <X> (f: (x:X) => X, xs: Array<X>): ?X => (
  xs.reduce(((b, x) => b ? b : f(x) ? x : null), null)
)

• babel-generator, babel-plugin-transform-flow-comments
  • #4504 Flow: Fix generating arrow functions with param. (@danharper)
• babel-register
  • #3685 Allow overwritting of sourceRoot. (@danez)
  • #4577 babel-register: update source-map-support to latest. (@MoOx)
• babel-core
  • #4570 Fix fileName options passed to babylon. (@DatenMetzgerX)
• babel-traverse
  • #4534 Fix issue with minified libraries and code coverage. (@withinboredom)
• babel-plugin-transform-es2015-destructuring
  • #4552 Fix destructuring evaluation with call expressions. (@danez)

We noticed that we can not make this optimizations if there are function calls or member expressions on the right hand side of the assignment since the function call or the member expression (which might be a getter with side-effect) could potentially change the variables we are assigning to.

[x, y] = [a(), obj.x];
// was tranforming to
x = a();
y = obj.x;
// now transforms to 
var _ref = [a(), obj.x];
x = _ref[0];
y = _ref[1];

• babel-types
  • #4587 Prevent flow-strip-types/flow-comments from removing entire ClassProperty. (@danharper)

💅 Polish

• babel-code-frame
  • #4579 babel-code-frame: Highlight strings with green (not red). (@lydell)
  • #4572 Improve syntax highlighting colors. (@lydell)

Before

After

🏠 Internal

Cleanup tests, remove various unused dependencies, do not run CI with only readme changes.

• babel-plugin-transform-es2015-modules-amd, babel-plugin-transform-es2015-modules-commonjs, babel-plugin-transform-es2015-modules-umd
  • #4543 Remove duplicate default error. (@kaicataldo)
• babel-generator, babel-plugin-transform-es2015-modules-amd, babel-plugin-transform-es2015-modules-commonjs, babel-plugin-transform-es2015-modules-systemjs, babel-plugin-transform-es2015-modules-umd, babel-plugin-transform-flow-strip-types
  • #4538 Fix tests with duplicate named exports. (@kaicataldo)
• babel-plugin-transform-es2015-function-name
  • #4532 Add tests for other module formats, from #4524. (@danharper)
• babel-plugin-transform-es2015-parameters, babel-traverse
  • #4519 Replace phabricator tickets with github ones in code comments. (@danez)
• babel-polyfill
  • #3694 Use plain js to do the pre/postpublish for the polyfill. (@danez)
• babel-preset-es2015
  • #4501 Remove ES2015 tests than do not parse in ES2016. (@TimothyGu)
• babel-plugin-transform-regenerator
  • #3703 Remove unused regenerator deps. (@hzoo)
• babel-code-frame
  • #3699 babel-code-frame: babel-runtime not necessary. (@hzoo)
  • #3696 Satisfy the "space-infix-ops" eslint rule. (@gigabo)
• babel-helper-transform-fixture-test-runner
  • #4560 Remove unused dependency babel-register. (@danez)
  • #3669 Do not include babel-register in test helper. (@danez)
• Other
  • #3693 remove unused packages (devDeps). (@hzoo)
  • #3681 Update shelljs to version 0.7.4 🚀. (@greenkeeperio-bot)
  • #4547 Internal: cancel build with only .md changes. (@hzoo)
  • #4565 Only exit if the TRAVIS_COMMIT_RANGE is not empty. (@danez)

Commiters: 20

First PRs!

• Alberto Piai (brainlock)
• Andy Kant (andykant)
• Basil Hosmer (bhosmer)
• Bo Borgerson (gigabo)
• Dan Harper (danharper)
• Kay J. (ksjun)
• Maxime Thirouin (MoOx)
• Micha Reiser (DatenMetzgerX)
• Moti Zilberman (motiz88)
• Rob Landers (withinboredom)
• Timothy Gu (TimothyGu)
• zenparsing (zenparsing)