`!obj.x` will return true for any falsy property - null, undefined,
positive or negative zero, NaN, and the empty string. `!(x in obj)` will
return true only if `x` is not an own property on `obj` nor anything in its
prototype chain. They are decidedly different tests and they check for
decidedly different things.
On Mon, Jul 9, 2018 at 9:08 PM, Naveen Chawla <naveen.c...@gmail.com> wrote:
> I don't use `in`.
>
> What do I get with `'x' !in obj` or `!(x in obj)` that I don't get with
> !obj['x'] ?
>
> Genuinely asking - I don't know what I am missing.
>
> I use obj[x] because I believe it's a more familiar syntax and I believe I
> get the same outcome..(?)..
>
> On Mon, 9 Jul 2018 at 22:41 Steve Fink <sph...@gmail.com> wrote:
>
>> +1 from me for !in. It's a surprisingly common nuisance.
>>
>> And I don't care for the !obj.x workaround at all -- even if you can
>> survive the difference in semantics, from a code reading point of view this
>> is saying something entirely different.
>>
>> And it is very different semantically. 'x' in obj does [[HasProperty]];
>> obj.x does [[GetProperty]]. With
>>
>> obj = { get x() { print("getter"); return 3; } };
>>
>> then |"x" in obj| does not print "getter" while |obj.x| does.
>>
>>
>> On 06/29/2018 12:26 AM, Cyril Auburtin wrote:
>>
>>
>> ```js
>> if (!obj.x && !obj.y) {
>> doit()
>> }
>> ```
>> The cases where they are equal to 0, '', null, undefined shouldn't matter
>> imo, if for example those x and y are numbers, they would be defined,
>> defaulted to 0, and you would test for `!== 0` rather if needed
>>
>> Le jeu. 28 juin 2018 à 18:31, Guylian Cox <guylian...@gmail.com> a
>> écrit :
>>
>>> I agree, it's very annoying to have to write it !(x in y). I've been
>>> wanting this operator for a very, very long time.
>>>
>>> If there is interest for !in, I think !instanceof deserves to be
>>> included too.
>>>
>>> Le jeu. 28 juin 2018 à 18:19, T.J. Crowder <tj.crowder@farsightsoftware.
>>> com> a écrit :
>>>
>>>> On Thu, Jun 28, 2018 at 5:14 PM, Tobias Buschor <
>>>> tobias.busc...@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()
>>>> > }
>>>>
>>>> There's
>>>>
>>>> ```js
>>>> if (!('x' in obj || 'y' in obj)) {
>>>> doit()
>>>> }
>>>> ```
>>>>
>>>> That said, I've wanted !in many a time, in a minor sort of way...
>>>>
>>>> -- T.J. Crowder
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>>>>
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