Small Proposal "!in"

[Michael Theriot]

I think it is irrelevant; the operator already exists and I would assume if
you want the negation of it you are using it correctly in the first place.
Otherwise are you not just arguing for its removal altogether? But to
answer your question one case that comes to mind is trapping get/has in a
proxy handler.

On Wednesday, July 18, 2018, Mike Samuel <mikesamuel at gmail.com> wrote:

>
>
> On Wed, Jul 18, 2018 at 11:05 AM Michael Theriot <
> michael.lee.theriot at gmail.com> wrote:
>
>> I think `in` and `instanceof` could both benefit from having negated
>> versions.
>>
>> Assuming the developer is using `in` correctly, hasOwnProperty concerns
>> are irrelevant. Either way they would attempt to use !(a in b), not
>> !hasOwnProperty.
>>
>
> Why should we assume the developer is using `in` correctly?
> Apologies if I buried my question at the end.  It was, what are the use
> cases for `in` that would not be better served by an ergonomic, infix
> hasOwnProperty?
>
>
> Same reason we don't use...
>> !(a == b) // a != b
>> !(a === b) // a !== b
>>
>
>
>> !(a > b) // a <= b
>> (!(a > b) && !(a == b)) // a < b
>>
>
> I'm not sure this is relevant to your larger point, and I've already
> conceded ergonomics, but
> these last two are not equivalent because NaN is weird.
>
> a = NaN, b = 0
> [!(a > b), a <= b]  // [true, false]
> [!(a > b) && !(a == b), a < b]  // [true, false]
>
>
>
>
>
>> On Thursday, June 28, 2018, Tobias Buschor <tobias.buschor at shwups.ch>
>> wrote:
>>
>>> I dont like to write:
>>> if ( !('x' in obj) &&  !('y' in obj) ) {
>>>      doit()
>>> }
>>>
>>> I was even tempted to write it that way:
>>> if ('x' in obj  ||  'y' in obj) { } else {
>>>      doit()
>>> }
>>>
>>> What about a !in operator to write it like this?
>>> if ('x' !in obj  &&  'y' !in obj) {
>>>      doit()
>>> }
>>>
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>>
>
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