Support for private field declarations?

[greggman]

• Rollup Version: 1.21.4
• Operating System (or Browser): N/A
• Node Version: 12.6.0

How Do We Reproduce?

rollup this code

class Foo {
  #p;
  constructor(v) {
    this.#p = v;
  }
  getV() {
    return this.#p;
  }
};

const a = new Foo('hello');
const b = new Foo('world');
console.log(a.getV(), b.getV());

repl

Expected Behavior

It rolls up

Actual Behavior

It gets a syntax error

Note: the code snippet above works in Chrome https://jsfiddle.net/greggman/z5w1pd9m/ and in node 12

$ node
Welcome to Node.js v12.6.0.
Type ".help" for more information.
> class Foo {
...   #p;
...   constructor(v) {
.....     this.#p = v;
.....   }
...   getV() {
.....     return this.#p;
.....   }
... };
undefined
> 
> const a = new Foo('hello');
undefined
> const b = new Foo('world');
undefined
> console.log(a.getV(), b.getV());
hello world
undefined
> 

[keithamus]

You can use the acornInjectPlugins option coupled with the acorn private class elements plugin to handle this:

import acornPrivateFields from 'acorn-private-class-elements'
export default {
    // … other options …
    acornInjectPlugins: [
        acornPrivateFields()
    ]
};

FWIW Private Fields are still a TC39 Stage 3 proposal and are not standardised ECMAScript (yet).

[greggman]

Oh, I thought the Chromium team had a policy not to ship any unapproved JavaScript features unless they were behind a flag (--experimental-javascript). Since they shipped private class fields not behind a flag in v74 I assumed that must mean the feature had passed some threshold of "approved" otherwise it would still be behind the flag

[lukastaegert]

I believe support in a major browser is a prerequisite for a Stage 3 feature to become Stage 4.

[shellscape]

Closing this one as resolved.