[Bug]: Parameter properties don't get transformed correctly / are broken

[danieltroger]

💻

• Would you like to work on a fix?

How are you using Babel?

Other (Next.js, Gatsby, vue-cli, ...)

Input code

const API_VERSION = 4;

class Bruh {
  public a_method(): void {
    console.log(this._version);
  }
  public constructor(
    public options: string,
    private readonly _version: number = API_VERSION
  ) {
    console.log(this.options);
  }
}
var instance = new Bruh("👀");
instance.a_method();

Configuration file name

babel.config.js

Configuration

module.exports = {
  presets: ["@babel/preset-typescript", "@parcel/babel-preset-env"]
};

🤔 Expected Behavior

👀 and then 4 is logged to the console.

😯 Current Behavior

undefined and then undefined is logged to the console.

Environment

Software	Version(s)
Parcel	2.0.0-nightly.912+145bfb82
Node	v17.0.1
npm/Yarn	3.1.0
Operating System	macOS 10.15.7 (19H1419)
@babel/core	7.16.0

Possible solution

Make so that it works correctly.

Additional context

parcel-bundler/parcel#7313

https://www.typescriptlang.org/docs/handbook/2/classes.html#parameter-properties

[babel-bot]

Hey @danieltroger! 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.

[danieltroger]

Wait is this a duplicate of #12066?

[danieltroger]

Bruh fml forreal? How am I supposed to find out that my code breaks because I have some stuff in the wrong order in a config file?

Why can't babel warn or do something that doesn't output broken code?

[JLHwung]

Closing this as a duplicate of #12066