Review requested:

• @nodejs/web-standards

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.32%. Comparing base (2cdea86) to head (57fda3b).
⚠️ Report is 6 commits behind head on main.

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- Coverage   90.32%   90.32%   -0.01%     
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  Files         730      730              
  Lines      234669   234704      +35     
  Branches    43946    43968      +22     
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+ Hits       211967   211987      +20     
- Misses      14417    14437      +20     
+ Partials     8285     8280       -5     

I don't think adding a check is worth it, I think the current behavior is fine actually, the spec requires a TypeError, we're throwing a TypeError (except for .language, indeed that's worth fixing). For reference, Chromium-based browsers throw TypeError: Illegal invocation

Errors from private fields are misleading and not future-proof: it's too easy to break 'implicit throw' unintentionally

It’s only true if that’s not covered by tests (which I would have expected WPT to cover, but I guess not, or at least not the subset we’re running)

Thanks for the reviews, the test now covers all getters via Object.keys(Navigator.prototype), so either approach is safe against future regressions of the .language kind.

I'm more into keeping the explicit ERR_INVALID_THIS checks for to maintain error message quality, instead of returning a internal field name, ERR_INVALID_THIS('Navigator') produces the same shape of message Chromium and FireFox emit, and matches what the rest of Node's brand-checked APIs throw

Here's what the error looks like on the browser side:

• Safari: TypeError: The Navigator.language getter can only be used on instances of Navigator
• Firefox: TypeError: 'get language' called on an object that does not implement interface Navigator.
• Chromium: TypeError: Illegal invocation

FWIW I'm in the Chromium camp, I think minimal effort is the appropriate amount of support we should spend on "passing an invalid this" use-case, so I'm not keen on adding a if that will slow down the happy path, ever so slightly – but it's certainly not a hill I want to die on for Navigator