Small Proposal "!in"

[Michael Theriot]

>
> For me, `hasOwn` with the different operand order isn't a problem, but
>> others may take a different view. Trying to keep the same order takes us
>> down a route like `inOwn` which I can't say I care for.
>>
>
> Nor me. I would argue for `on` (`'a' on b`), but that is a huge typo
> footgun (especially for Colemak users) and maybe isn't clear enough about
> its semantics.  I would argue that operators aren't camel cased in JS
> though, so `hasown`/`inown`.
>

For what it's worth I was also thinking of an "on" operator when reading
this message, so this is intuitive to me. I also think that is a separate
idea to propose though.

Of couse the usage of `in` is most of the time is not recommended, but it
>> has it place.
>>
>
> What places does it have?
> I remain unconvinced that `in` has significant enough use cases to warrant
> high-level ergonomics
> were it being proposed today.
>
> It exists, and it'll probably never be removed from the language, but I
> don't think it should be taught
> as a good part of the language, and linters should probably flag it.
>

Maybe a radical thought, but does this not apply to hasOwnProperty? If you
have strong type management why test for a property? The one case I can
think of is parsing JSON but I handle that with destructuring. Are there
significant use cases for it? Should linters flag it?
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