No, the hash is a red herring. It's a way of signifying a private field on an object.

Ah. Thanks, that hint pointed me to [1]. Seems like it's been supported by every major browser since 2021, and only specified in the upcoming ECMAScript 2026 spec.

[1] https://developer.mozilla.org/en-US/docs/Web/JavaScript/Refe...

It has a contentious history and largely was forced through by one person in TC39 who focused on a particular corner case