There's several ways proxies can change the result of `in`:
- Directly via `handler.has(target, key)` (returns boolean)
- Indirectly via `handler.getOwnPropertyDescriptor(target, key)` (returns
existing descriptor or `undefined` if missing)
- Indirectly via `handler.getPrototypeOf(target)' (returns relevant
prototype)
The proxy trap `has` is almost a direct substitute for your
`Symbol.inObject` in most cases, provided you're okay with keys getting
stringified.
On Thu, May 9, 2019 at 17:17 Tom Barrasso <t...@barrasso.me> wrote:
> Thanks interesting, I hadn’t realized it was possible to “trap” the in
> operator using Proxy. I may be wrong, but I don’t think Proxy is capable of
> operating on the prototype chain. Specifically, I don’t think you can
> change the behavior of the in operator for all Strings (which I’m sure many
> would prefer).
>
> If this Symbol were seriously considered I believe it would expand the
> meaning of the in operator as you’re correct, this is definitely not it’s
> current intention.
>
> Tom
>
> On Thu, May 9, 2019 at 4:39 PM Claude Pache <claude.pa...@gmail.com>
> wrote:
>
>>
>>
>> Le 9 mai 2019 à 20:52, Tom Barrasso <t...@barrasso.me> a écrit :
>>
>> Like Symbol.hasInstance but for the "in" operator.
>> This symbol would work for both native and user-defined objects.
>>
>> **Example implementation** prototyping native object:
>>
>> ```js
>> String.prototype[Symbol.inObject] =
>> function(searchString) {
>> return this.includes(searchString)
>> }
>> ```
>>
>>
>> **Example implementation* *for user-defined object:
>>
>> ```js
>> function range(min, max) => ({
>> [Symbol.inObject]: (prop) => {
>> return (prop >= min && prop <= max)
>> }
>> })
>> ```
>>
>>
>> **Example usage**:
>>
>> ```js
>> ("foo" in "food") // true
>> (14 in range(1, 25)) // true
>> ```
>>
>>
>> Those two examples seem to give to the `in` operator a meaning that it
>> was not intended to have. The `in` operator is specifically meant to check
>> whether a given property exists in a given object.
>>
>> Also, there already exists a way to customise the behaviour of the `in`
>> operator, namely by using a Proxy.
>>
>> —Claude
>>
> _______________________________________________
> es-discuss mailing list
> es-discuss@mozilla.org
> https://mail.mozilla.org/listinfo/es-discuss
>
--
-----
Isiah Meadows
cont...@isiahmeadows.com
www.isiahmeadows.com
_______________________________________________
es-discuss mailing list
es-discuss@mozilla.org
https://mail.mozilla.org/listinfo/es-discuss
