Small Proposal "!in"
sphink at gmail.com
Mon Jul 23 23:28:25 UTC 2018
This reads a little oddly, but another syntax option would be `prop
in.own obj` (equivalent to `obj.hasOwnProperty(prop)`) and then `prop
Or perhaps `in.own` should be Object.prototype.hasOwnProperty.call(obj,
Though this makes me think it would be nice to have something like `name
in.map mymap` (equivalent to `mymap.has(name)`)
On 07/20/2018 10:09 AM, Augusto Moura wrote:
> The only use that came to mind was detecting a property descriptor in
> a prototype chain. Sure is not a day to day use case, but it's useful
> when writing libraries that involve descriptor modifications
> (decorators, for example, will largely involve it). Recently I had to
> get the descriptor of properties in a potencial deep inheritance
> (current Object helpers only return own descriptors), and used the
> `in` operator to guard the prototype recursive search.
> ``` js
> const searchRecursivelyPropDescriptor = (obj, prop) =>
> ? undefined
> : Object.getOwnPropertyDescriptor(obj, prop) ||
> searchRecursivelyPropDescriptor(Object.getPrototypeOf(obj), prop);
> const getPropertyDescriptor = (obj, prop) =>
> prop in obj ? searchRecursivelyPropDescriptor(obj, prop) : undefined;
> Anyways, we can't simply ignore the operator, if we are getting a
> `!instance` and opening precedence to future operators (`!on` or
> `!hasOwn`) I don't see any problems with a `!in`. Legacy bad design
> should not affect language consistency of new features.
> Em qui, 19 de jul de 2018 às 12:07, Mike Samuel <mikesamuel at gmail.com
> <mailto:mikesamuel at gmail.com>> escreveu:
> On Thu, Jul 19, 2018 at 10:40 AM Augusto Moura
> <augusto.borgesm at gmail.com <mailto:augusto.borgesm at gmail.com>> wrote:
> Of couse the usage of `in` is most of the time is not
> recommended, but it has it place.
> What places does it have?
> I remain unconvinced that `in` has significant enough use cases to
> warrant high-level ergonomics
> were it being proposed today.
> It exists, and it'll probably never be removed from the language,
> but I don't think it should be taught
> as a good part of the language, and linters should probably flag it.
> Augusto Moura
> es-discuss mailing list
> es-discuss at mozilla.org
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