Small Proposal "!in"

[Michael Theriot]

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.

Same reason we don't use...
!(a == b) // a != b
!(a === b) // a !== b
!(a > b) // a <= b
(!(a > b) && !(a == b)) // a < b

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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