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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