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Babel 8 Release Plan #10746

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25 of 34 tasks
nicolo-ribaudo opened this issue Nov 21, 2019 · 48 comments
Open
25 of 34 tasks

Babel 8 Release Plan #10746

nicolo-ribaudo opened this issue Nov 21, 2019 · 48 comments

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@nicolo-ribaudo
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nicolo-ribaudo commented Nov 21, 2019

We plan to release a new major version in 2021 (milestone).

This release won't have all the migration pain which there was while migrating from Babel 5 to Babel 6 and then from Babel 6 to Babel 7. We plan to only make a few breaking changes, and provide an easy migration strategy for each of them. Because of this, you won't see ~80 prereleases like we did in for Babel 7.0.0, but we plan to only release a few of them.

Babel 8.0.0 will only contain breaking changes: we will release a minor version the same day, containing all the bug fixes and new features that would otherwise be released in 8.0.0.

This document is still a work in progress, but you can already start by applying the suggested migration strategies to your own codebase.

  • Compilation breaking changes

    • Don't remove uninitialized class fields when using Flow/TS (pr for flow: #10120, pr for TS: #11114)

      • Area: Flow and TypeScript transforms

      • Impact: High (only for flow and TypeScript users)

      • Migration:
        You can use the new declare syntax, introduced in TypeScript 3.7 (Babel 7.7) and in Flow 0.120 (Babel 7.9), if you don't want fields to be initialized to undefined:

        class A {
          foo: string | void; // initialized to undefined
          declare bar: number; // type-only
        }

        Note that while this syntax is enabled by default in @babel/parser when using the typescript or flow plugins, if you are using Babel to remove type annotations you must enable the allowDeclareFields option:

        // TypeScript
        {
          presets: [
            ["@babel/typescript", { "allowDeclareFields": true }]
          ]
        }
        
        // Flow
        {
          presets: [
            ["@babel/flow", { "allowDeclareFields": true }]
          ]
        }
    • Disallow sequence expressions inside JSX attributes (pr: #8787)

      • Area: JSX, @babel/parser
      • Impact: Low
      • Migration: If you are using them, you can already wrap them in parentheses:
        <div key={foo, bar}></div> // Invalid
        <div key={(foo, bar)}></div> // Valid
    • Disallow } and > in JSX text (pr: feat(babel-parser): throw syntax error for } and > in JSX text #11046)

      • Area: @babel/parser with JSX
      • Impact: Low
      • Migration: You can use {'}'} and {'>'} instead.
      • Notes: This is technically a bug fix becase the specification already forbids them. However, we have chosen to postpone it until Babel 8 because it could break someone's code.
    • Transforms JSX spread properties using object spread (pr: #11141, docs: website#2289)

      • Area: JSX
      • Impact: Medium
      • Migration: You can already have this behavior by using the useSpread option in Babel 7.7.0. If your code needs to run in an environment which doesn't support object spread, you can either use @babel/preset-env (recommended) or @babel/plugin-proposal-object-rest-spread. If you want to transpile Object.assign down to Babel's _extends helper (which is the current default behavior) you also need to enable @babel/plugin-transform-object-assign.
    • Use the new JSX implementation by default (pr: #11436, docs: website#2289)

      • Area: JSX
      • Impact: High
      • Migration: Starting from Babel 7.9.0, you can pass the runtime: "classic" option to @babel/preset-react or @babel/plugin-transform-react-jsx to be explicit about your usage of createElement (or the equivalent function in other libraries).
        If you are using a modern enough version of React or Preact, you can already use the new runtime: "automatic" implementation.
    • Parse JSX elements when both the JSX and TS plugins are enabled, and throw an error when both Flow and TS are enabled (pr: #11316)

      • Area: JSX, TypeScript
      • Impact: Low
      • Migration: If you don't want <Foo> to be parsed as a JSX element, but as a TypeScript typecast, you can disable the JSX plugin.
      • Note: The current behavior is that JSX parsing is only handled by the isTSX option of the TypeScript plugin. We are also removing this option. We think that having the JSX plugin control JSX parsing is less confusing for our users.
    • Remove moduleAttributes support (pr: #13308)

      • Area: Import assertions ES proposal
      • Impact: Low
      • Migration: Replace @babel/plugin-syntax-module-attributes by @babel/plugin-syntax-import-assertions: you can already start doing this in Babel 7. After you replace the plugin, you should search the following patterns in your codebase
      import value from "module" with type: "json";

      and replace them by

      import value from "module" assert { type: "json" };

      If you are not using @babel/plugin-syntax-module-attributes, you don't need to do anything.

    • Remove support for the 2018-09 decorators proposal (pr: #12712)

      • Area: @babel/plugin-proposal-decorators
      • Impact: Medium
      • Migration: You should migrate to the new version of the proposal. The syntax is the same, but you will need to rewrite your decorator functions. You can already migrate since Babel 7.17.0, using the "version": "2021-12" option of @babel/plugin-proposal-decorators.
  • Configuration breaking changes

    • Require @babel/plugin-proposal-dynamic-import when transforming import() to SystemJS (#12700)
      • Area: @babel/plugin-transform-modules-systemjs
      • Impact: Medium
      • Migration: Add @babel/plugin-proposal-dynamic-import to your config: you can already do it in Babel 7. If you are using @babel/preset-env, you don't need to do anything.
      • Notes: All the other plugins which support dynamic import (transform-modules-commonjs and transform-modules-amd) require the separate plugin since it was introduced. We couldn't change it for transform-modules-systemjs because that package did already support dynamic import.
    • Use defaults, not ie 11 as default targets
      • Area: @babel/preset-env
      • Impact: Medium
      • Migration: If you are already using targets or have a .browserslist config file, this change won't affect you. Otherwise, you'll probably be fine with the new behavior (which supports these modern browsers). Note that the default targets does not include IE. If you still need to support IE, please specify IE 11 in targets. If you need to enable every possible plugin for even older browsers, you can already enable the forceAllTransforms option.
    • Remove uglify target (pr: #10895, docs: website#2290)
      • Area: @babel/preset-env
      • Impact: Low
      • Migration: The uglifyjs target had been deprecated since 7.0.0-beta.0, if you still need this, you can enable the forceAllTransforms option.
    • Move root AMD/UMD/SystemJS options to be plugin/preset options (pr: Allow defining the moduleIds-related option in the transform plugins #11194, [babel 8] Remove module-specific options from @babel/core #12724)
      • Area: @babel/core, @babel/cli, @babel/plugin-transform-modules-amd, @babel/plugin-transform-modules-umd, @babel/plugin-transform-modules-systemjs
      • Impact: Medium
      • Migration: When upgrading to Babel 8, you'll move to modify your config and pass these options to the correct plugin or preset.
        If you are passing these options using the cli, you'll need to create a configuration file.
    • Drop support for core-js 2 (pr: #11751)
      • Area: @babel/preset-env, @babel/plugin-transform-runtime, @babel/compat-data
      • Impact: High
      • Migration: You can already change your config to use core-js@3. Don't forget to npm install it!
      • Notes:
        1. When useBuiltIns is enabled, the default core-js version is now 3.6 instead of 2
        2. If you still need core-js@2 support, you can use babel-plugin-polyfill-core-js2.
    • Add mandatory version option to the decorators plugins, and merge the two plugins in @babel/parser.
    • Better file extension handling for TS and Flow presets (pr: #14955)
      • Area: @babel/preset-typescript, @babel/preset-flow, @babel/plugin-transform-typescript, @babel/plugin-transform-flow-strip-types
      • Impact: Medium
      • Migration:
        • You can already avoid enabling both the TS and Flow plugins on the same file, using the overrides option (this is not necessary if you are using the presets, and not directly the plugins)
        • When migrating to Babel 8, you can remove the isTSX option from @babel/preset-typescript and instead enable the relevant JSX preset/plugin.
      • Notes: See the PR description for more details.
  • API breaking changes

  • AST breaking changes

    • Use an identifier for TSTypeParameter.name (#12829)

      • Area: @babel/parser
      • Impact: High for customized Babel plugin depending on TypeScript TSTypeParameter, e.g. the T in function f<T>() {}
      • Notes: For a TS type parameter node, node.name is a string in Babel 7 while in Babel 8 it is an Identifier
      • Migration: If you have a customized plugin accessing the name of a type parameter node, use node.name.name in Babel 8.
    • Rename parameters to params, typeAnnotation to returnType for TSCallSignatureDeclaration, TSConstructSignatureDeclaration, TSFunctionType, TSConstructorType and TSMethodSignature
      (#9231) (pr: #13709)

      • Area: @babel/parser
      • Impact: High for customized Babel plugin depending on these TS nodes:
      interface Foo {
        // TSCallSignatureDeclaration
        <T>(): string;
      
        // TSMethodSignature
        foo<T>(): string;
      
        // TSConstructSignatureDeclaration
        new <T>(): string;
      }
      
      // TSFunctionType
      type Bar = <T>() => string;
      
      // TSConstructorType
      type Baz = new <T>() => string;
      • Migration: If you have a customized plugin accessing properties of these TS nodes, make adjustments accordingly:
        • For node.parameters in Babel 7, use node.params in Babel 8
        • For node.typeAnnotation in Babel 7, use node.returnType in Babel 8
  • Misc breaking changes

    • Bump peer dependency on @babel/core to ^8.0.0
      • Area: Every package
      • Impact: None if you update every @babel/* package
    • ESM runtime helper files should have the .mjs extension
      • Area: @babel/runtime, @babel/runtime-corejs2, @babel/runtime-corejs3
      • Impact: Medium
      • Notes: ES Modules are now unflagged (nodejs/node#29866), and .js modules don't work with native import unless our package.json specifies type: "module" (which will break cjs helpers).
    • Change the format of CommonJS helpers in @babel/runtime
      • Area: @babel/runtime, @babel/runtime-corejs2, @babel/runtime-corejs3
      • Impact: Low
      • Notes: This will only affect you if you are using @babel/runtime 7.x with @babel/plugin-transform-runtime 8.x (or the other way around), which woudln't be supported anyway.
    • Disallow importing internal files of the different packages (pr: #14013)
      • Area: Every package
      • Impact: High
      • Notes: This will break at least vue-cli (cc @sodatea) and ember-cli-babel [2] (cc @rwjblue). We will provide targets-parser as a separate helper in v7.8.0.
        ⚠️ If anyone else is relying on internal Babel files, please let us know!
    • Output non-ASCII characters as-is in string literal (pr: #11384)
      • Area: @babel/generator
      • Impact: High only if you are manually calling the babel.transform API and your server is not serving js files in the utf8 encoding.
      • Notes: If you are using any one of @babel/cli, WebPack, Rollup, create-react-app or other Node.js powered bundlers, the transformed code is always encoded with utf-8. That said, this issue probably won't affect your app.
      • Mitigation: Ensure your server is always serving js files in the utf8 encoding. If you can not control the server output, use <script charset="utf-8" src="your-app.js"></script> in the html files. You may also restore to the Babel 7 behaviour by
        {
          generatorOpts: {
            jsescOption: {
              minimal: false
            }
          }
        }
    • Align Babel parser error codes between Flow and TypeScript (pr: #13294)
      • Area: @babel/parser
      • Impact: Low. It has an effect only if you handle the Babel parsing error when error.code is OptionalBindingPattern .
      • Mitigation The error.code for OptionalBindingPattern is renamed as PatternIsOptional.
  • Other possibly breaking changes

    • Remove ts type imports on Program:exit (pr: #10009, #12706)
      • Area: @babel/plugin-transform-typescript
      • Impact: Low
    • Allow skipped NodePaths to be requeued (pr: #13291)
      • Area: @babel/traverse
      • Impact: Low
      • Notes: This is actually a bugfix, but it causes an infinite loop in the tdz implementation of @babel/plugin-transform-block-scoping
    • Look for comments containing "Babel 8" in the source code
      • Area: Every package
      • Impact: Low
      • Notes: Most of those comments are just for internal dependencies between packages. Any significant change will have a dedicated point in this list of breaking changes.

Related: #10752


Note for contributors

~~We implement Babel 8 breaking changes under the BABEL_8_BREAKING env flag. To test the breaking changes, please duplicate the affected tests with the -babel-7 suffix and add BABEL_8_BREAKING: false to test options. The breaking changes will be merged to the main branch but stripped before publishing. ~~

@nicolo-ribaudo nicolo-ribaudo added this to the Babel 8.x milestone Nov 21, 2019
@JLHwung JLHwung pinned this issue Nov 21, 2019
@TrejGun
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TrejGun commented Nov 22, 2019

Remove ts type imports on Program:exit

will this allow to generate .d.ts files?

@nicolo-ribaudo
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@TrejGun It is totally unrelated I think. I'd be happy to hear more about it on our Slack!

@fwh1990
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fwh1990 commented Dec 2, 2019

Will 8.x be faster than 7.x when building my own project?

@nicolo-ribaudo
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nicolo-ribaudo commented Dec 2, 2019

No. Version 8.0 will only contain breaking changes, so if there are any performance improvements that we can make they will also be included in 7.x.

@Andarist
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Andarist commented Dec 4, 2019

I would like to propose a breaking change.

I believe that @babel/runtime helpers should not get special treatment when transpiled to CJS - at least not for their export shape (used requires etc can still be optimized). I propose such output:

+"use strict";
+exports.__esModule = true;
+exports.default = _toPropertyKey;

-var _typeof = require("../helpers/typeof");
+var _typeof = require("../helpers/typeof").default;

-var toPrimitive = require("./toPrimitive");
+var toPrimitive = require("./toPrimitive").default;

function _toPropertyKey(arg) {
  var key = toPrimitive(arg, "string");
  return _typeof(key) === "symbol" ? key : String(key);
}

-module.exports = _toPropertyKey;

With such ESM-compatible output we could try to explore removing useESModules option from @babel/plugin-transform-runtime because it's possible to create a "proxy" package.json that would allow bundlers & node to pick up the correct version of a particular helper on their own using a single path (that would be inserted by transform runtime). The directory structure could look smth like this

helpers/toPropertyKey/package.json
helpers/toPropertyKey/toPropertyKey.js
helpers/toPropertyKey/toPropertyKey.mjs

with package.json being:

{
  "name": "@babel/runtime/helpers/toPropertyKey",
  "private": true,
  "type": "module",
  "main": "./toPropertyKey.cjs.js",
  "module": "./toPropertyKey.js",
  "exports": {
    ".": {
      "require": "./toPropertyKey.cjs.js",
      "default": "./toPropertyKey.js"
    }
  }
}

@XaveScor
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@babel/preset-env using core-js@2 by default. Can @bable/preset-env@8 using core-js@3 only?

@nicolo-ribaudo
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Yeah, this is a good idea!
@zloirock WDYT about dropping support for core-js@2?

@zloirock
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Yes, core-js@2 support should be dropped and the version of core-js should be required argument with useBuiltIns in preset-env. Maybe it could be good also to enforce specifying of minor core-js version.

@zloirock
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Why it should be dropped - copy-paste from the draft of one post:

core-js@3 was published 10 months ago - I hoped that this is enough to update. However, core-js@2 still is used more often than core-js@3 - if some dependencies depend on core-js@2, users don't wanna have some copies of core-js in the bundle. However, we should kill core-js@2 ASAP. The main reason is even not some bugs, it's... V8 (de)optimizations - even if nothing is polyfilled. WTF? Now, if V8 saw the usage of some non-often used features (like @@species pattern), for example, in the features detection - V8 always will use the non-optimized version of a method that theoretically could use it. In core-js@2, that affects regexes, iterators, some array methods, typed arrays, promises, etc... Sometimes that causes ~100x performance degradation, let's say thanks to V8. At this moment, V8 is the most popular JS engine, so it's a complex of critical issues. Workarounds for a big part of those deoptimizations were added in core-js@3.0, for remaining - at the latest patch releases. I don't see any reason to spent many days fixing those (and other) issues in the obsolete version.

sodatea added a commit to sodatea/vue-cli that referenced this issue Feb 3, 2020
As planned in babel/babel#10746,
in babel 8 the old `loadPartialConfig` can't be used synchronously.
sodatea added a commit to vuejs/vue-cli that referenced this issue Feb 3, 2020
…abel 8 (#5133)

* refactor: use babel.loadPartialConfigSync (added in babel 7.8)

As planned in babel/babel#10746,
in babel 8 the old `loadPartialConfig` can't be used synchronously.

* refactor: remove dependence on internal babel files, preparing for babel 8

See
babel/babel#10746
babel/babel#10899
sebinsua added a commit to sebinsua/perspective that referenced this issue Feb 5, 2020
We should upgrade core-js@2 to core-js@3 because the (1) the next major
release of Babel will do so, and (2) there are many V8 de-optimizations
in core-js@2 that have been fixed in core-js@3.

See: babel/babel#10746 (comment)
See: babel/babel#10746 (comment)
See: https://github.com/zloirock/core-js/blob/master/docs/2019-03-19-core-js-3-babel-and-a-look-into-the-future.md

We also bumped Babel to 7.8.4 because it was only after 7.4 that
core-js@3 was supported.

See: https://babeljs.io/blog/2019/03/19/7.4.0#core-js-3-7646-https-githubcom-babel-babel-pull-7646
@Pranav2612000
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Hey. I would love to contribute to Babel 8. What are some easy features I can work on? I think I can work on :-

Look for comments containing "Babel 8" in the source code
Area: Every package
Impact: Low
Notes: Most of those comments are just for internal dependencies between packages. Any significant change will have a dedicated point in this list of breaking changes.

Are there any other issues I can contribute to and help?

@nicolo-ribaudo
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nicolo-ribaudo commented Feb 6, 2020

Another good one could be #9546, which would give you the chance to dig into @babel/parser's internals.
Or maybe Disallow using babel.transform, babel.transformFile, babel.transformFromAst, babel.parse, babel.loadOptions and babel.loadPartialConfig synchronously, which is probably a bit easier.
If you prefer, Transforms JSX spread properties using object spread involves removing the useSpread option and making it the default behavior.

If you want to work on the TODOs left in the comments containing "Babel 8", please don't resolve all of them in a single PR but keep separate changes in different PRs.

@Pranav2612000
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Disallow using babel.transform, babel.transformFile, babel.transformFromAst, babel.parse, babel.loadOptions and babel.loadPartialConfig synchronously
Area: @babel/core
Impact: Medium
Migration: You can use babel.transformSync, babel.transformFromAstSync and babel.transformFileSync, supported since version 7.0.0. babel.parseSync, babel.loadOptionsSync and babel.loadPartialConfigSync will be introduced in v7.8.0.

Shoud I just delete the given functions? Or am I misunderstanding the requirements?

@nicolo-ribaudo
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Currently they behave asynchronously if you pass them a callback, otherwise they behave synchronously. Only the callback-based version should be allowed.

mactanxin pushed a commit to mactanxin/vue-cli that referenced this issue Feb 11, 2020
…abel 8 (vuejs#5133)

* refactor: use babel.loadPartialConfigSync (added in babel 7.8)

As planned in babel/babel#10746,
in babel 8 the old `loadPartialConfig` can't be used synchronously.

* refactor: remove dependence on internal babel files, preparing for babel 8

See
babel/babel#10746
babel/babel#10899
@cpojer
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cpojer commented May 13, 2020

@hzoo I think that's a great idea, thank you for thinking about this.

@Airkro
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Airkro commented May 27, 2020

How about drop support for core-js 3 (in preset-env). We have babel-plugin-polyfill-corejs3 now.

@nicolo-ribaudo
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That was one of my goals when I started working on the polyfill packages, but we should first do babel/rfcs#2

@xiaoxiangmoe
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When will babel 8 release?

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@fabis94
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fabis94 commented Oct 14, 2020

Would be nice to know when we can expect Babel 8. The OP says that it'll come out in 2020, but the year is soon coming to a close and there's no news yet.

@WillBeebe
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Who else is pumped for the chokidar dependency bump? :D

@nicolo-ribaudo
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@fabis94 Sorry for the lack of communication about a precise schedule. My hope is to release Babel 8 alongside with 7.13 (so in about 2 months), since there isn't much left to do. However, please don't take this as an hard deadline since anything could happen 🙏

@WillBeebe Starting from Babel 7.12.0, it will use chokidar@3 if you are using a modern Node.js version 😉 #11560

@fabis94
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fabis94 commented Dec 16, 2020

Any updates regarding this?

@nicolo-ribaudo
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nicolo-ribaudo commented Dec 16, 2020

Yes!
We wanted to work on this in a separate branch next-8-dev/next-8-rebased, but we found out that it was really slowing us down. We are now starting to add these Babel 8 changes to main, so that it's easier for us to work on them and hopefully will help us finish this release in a reasonable time.

@jridgewell
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One more thing that's always bugged me: we should rename OVERWRITE to TEST_OVERWRITE. It doesn't make sense to use make test-only TEST_ONLY=class-properties TEST_GREP=public OVERWRITE=true

@nicolo-ribaudo
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No need to wait for Babel 8, we can add an alias now.

@rnarkk
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rnarkk commented Jul 2, 2021

Would you mind updating the current progress of the task list? Some of them seem to have already been solved.

@Ontopic
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Ontopic commented Aug 18, 2021

Yes!
We wanted to work on this in a separate branch next-8-dev/next-8-rebased, but we found out that it was really slowing us down. We are now starting to add these Babel 8 changes to main, so that it's easier for us to work on them and hopefully will help us finish this release in a reasonable time.

So in order to play around with where things are at, will a @next or ^7.15 bring me the closest?

@JLHwung
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JLHwung commented Aug 18, 2021

So in order to play around with where things are at, will a @next or ^7.15 bring me the closest?

7.15 has been published but it will not contain Babel 8 breaking changes, as required by semver. We don't have Babel 8 nightly build, but we have Babel 8 e2e test on popular libraries:

e2e-breaking-babel:
you can fork Babel repo and run e2e test on your own library to see if Babel 8 will break. Feedbacks are always welcome.

@Ontopic
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Ontopic commented Aug 18, 2021

Thanks! Long time since I last build Babel myself. Let's see the dev contributor experience nowadays :)

@Semigradsky
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Bump Node Support to >=12.19

Should it be updated to >=14? 12's EOL is 2022-04-30.

@nicolo-ribaudo
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nicolo-ribaudo commented Apr 16, 2022

Yes thanks, we are a few years late with this release! 🙃

(If it takes another year we can also drop Node.js 14 👀)

@dlong500
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I hate to be that guy, and I know that ultimately a release is ready when it's ready, but given the timeframe here can we get an update on where things stand? The Babel Roadmap page hasn't been updated since 2021 (at which point there was a note about how long it had already been taking and how the release was "closer than ever").

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