Cc the list... On Aug 25, 2014 6:06 PM, "Isiah Meadows" <[email protected]> wrote:
> There really shouldn't be any sort of object construction needed to check > types like this. `isa` may be better, anyways, but I still find that > requirement to build and destroy an object to check somewhat > counterproductive. > > Andrea gets what I'm talking about. Also, another (possibly separate) > proposal would be to make cases like `"foo" instanceof String" === true` > instead of their current behavior, throwing a TypeError. (I believe...I'm > on a phone, not a PC where I can test. Correct me if I'm wrong.) > On Aug 25, 2014 5:03 AM, "Andrea Giammarchi" <[email protected]> > wrote: > >> I know it's just a sketch but that `Object.prototype.is` does not play >> well with `Object.create` where no constructor is necessary to create `is` >> relations. >> >> Regards >> >> >> On Sun, Aug 24, 2014 at 10:15 PM, C. Scott Ananian <[email protected] >> > wrote: >> >>> On Sun, Aug 24, 2014 at 4:04 PM, Isiah Meadows <[email protected]> >>> wrote: >>> > There is no way currently to reliably verify types in JS. Type >>> annotations >>> > cannot solve this completely, especially when you have an overloaded >>> > function. A way to reliably verify types would make this far easier. >>> So far, >>> > here are the current options with their respective caveats: >>> > >>> > 1. `instanceof` - This returns true for the class, but also for >>> subclasses. >>> > This isn't always desired. >>> >>> Your proposal fixes this, but does not address the other issues you >>> raise: >>> >>> > 2. `this.constructor === Foo` - The constructor property could easily >>> be >>> > overwritten, rendering this relatively useless. >>> >>> `Object.getPrototypeOf(this) === Foo.prototype` is the test which >>> `instanceof` uses. >>> Does not require new syntax. >>> >>> > 3. `typeof` - This only is useful for literals, with the exception of >>> > `null`. >>> >>> Your proposed `is` operator is not useful for literals. >>> >>> > 4. `Object.prototype.toString.call()` - This returns the correct native >>> > object type for native objects, but returns `[object Object]` for all >>> > non-native objects, rendering it effectively useless. This includes >>> object >>> > instances created from `class Foo {}`, etc. >>> >>> In general, you can always define: >>> ``` >>> Object.prototype.is = function(constructor) { >>> return Object.getPrototypeOf(this) === constructor.prototype; >>> }; >>> ``` >>> rather than try to use toString. Unless you want it to work on >>> literals... >>> --scott >>> _______________________________________________ >>> es-discuss mailing list >>> [email protected] >>> https://mail.mozilla.org/listinfo/es-discuss >>> >> >>
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