Hey @bradennapier! 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
community that typically always has someone willing to help. You can sign-up here
for an invite.

It's probably a bug with one of your dependencies (you can find it in the stack trace), which is importing core-js (and it is relying on core-js@2) without specifying it in their dependencies.

EDIT: It is a bug with the @auroradao/logger package (though I can't confirm it because I couldn't find it on npm): on line 9 of @auroradao/logger/dist/constants.js this library is requireing core-js/modules/es7.symbol.async-iterator (which only existed in core-js@2), but I bet that @auroradao/logger/package.json doesn't contain core-js@2 in the "dependencies" section.

Sweet, thanks! Makes sense and yeah that is a private package. Thanks!

Note to anyone doing this - I had to delete my node_modules when changing to core-js 3 or i got the following errors:

TypeError: [BABEL] /Users/Shared/Development/projects/task-handler/src/constants.js: (0 , _semver(...).coerce) is not a function

Guessing it is a cache issue, not quite sure.

Yeah, that is our fault 😛 It's fixed on master and it will be in the next release. In the meantime, as you mentioned, reinstalling node_modules should be enough.

Thanks, easy enough to fix :) . Appreciate all you guys do!

corejs option is not documented here

corejs option is not documented here

concretely, the set of options sent to @babel/preset-env needs to have this property like so:

{
  "presets": [
    "@babel/preset-flow",
    [
      "@babel/preset-env",
      {
        "targets": {
          "node": "8.10"
        },
        "corejs": "2", // <---
        "useBuiltIns": "usage"
      }
    ]
  ]
}

along with the dependency in package.json

core-js@3 is a big new release with tighter integration into babel, worth reading the blog post: https://github.com/zloirock/core-js/blob/master/docs/2019-03-19-core-js-3-babel-and-a-look-into-the-future.md

Since @babel/preset-env now supports core-js@2 and core-js@3, useBuiltIns requires setting a new option, corejs, which specifies the used version (corejs: 2 or corejs: 3). If it isn't directly set, corejs: 2 will be used by default and it will show a warning.

Came here looking for help on this one for Symfony Webpack throwing this warning. In Symfony webpack.config.js add the following:

    .configureBabel((babelConfig) => {
        const preset = babelConfig.presets.find(([name]) => name === "@babel/preset-env");
        if (preset !== undefined) {
            preset[1].useBuiltIns = "usage";
            preset[1].corejs = '3.0.0';
        }
    })

This appears to have removed the warning.