[Feature] Update babel config to include private methods proposal plugin

Could private class fields be added to the babel config for tests? It is included in @babel/preset-env and is a stage 4 proposal now which should be integrated into the standard soon.

Moved from comment in #11440.

$ playwright test
Using config at .../playwright.config.ts

SyntaxError: .../index.ts: Class private methods are not enabled.
  81 |   }
  82 |
> 83 |   get #log() {
     |   ^
  84 |     return this.#logger
  85 |   }
  86 |

[pavelfeldman]

This did not make it into Playwright v1.19, we cut several days ago. So you’ll need to either use @playwright/test@next or wait for v1.20 (mid March).

[pavelfeldman]

Yep, I can repro. I think I had my test case with the .js extension by accident.