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transform-module-commonjs breaks this in private class property values by default #9856

coreyfarrell opened this Issue Apr 14, 2019 · 2 comments


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commented Apr 14, 2019

Bug Report

Current Behavior
@babel/plugin-transform-module-commonjs views private class properties as being in 'top-level' scope, replaces this with void 0. Issue found when testing code against node.js 12 which has native support for class properties.

Input Code

export class Example {
  notPrivate = this;
  #private = this;

Expected behavior/code
The value set to #private is not a "top-level this" so should be untouched by default, just as the value of notPrivate is untouched.

Babel Configuration (.babelrc, package.json, cli command)

	"plugins": [


  • Babel version(s): 7.4.3
  • Node/npm version: node 10.15.3, npm 6.4.1 / node v12.0.0-nightly20190411655c90b287, npm 6.9.0
  • OS: Fedora 28
  • Monorepo: no
  • How you are using Babel: tested with CLI, register and REPL.

Possible Solution
A work-around is to set allowTopLevelThis: true option to @babel/plugin-transform-modules-commonjs.


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commented Apr 14, 2019

Hey @coreyfarrell! We really appreciate you taking the time to report an issue. The collaborators
on this project attempt to help as many people as possible, but we're a limited number of volunteers,
so it's possible this won't be addressed swiftly.

If you need any help, or just have general Babel or JavaScript questions, we have a vibrant Slack
that typically always has someone willing to help. You can sign-up here
for an invite.


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commented Apr 14, 2019

I found the cause of this in @babel/helper-module-transforms, created a fix and manually tested. I'm just working on adding automated tests before opening a PR.

coreyfarrell added a commit to coreyfarrell/babel that referenced this issue Apr 14, 2019

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