> Le 9 mai 2019 à 20:52, Tom Barrasso <[email protected]> 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
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