as Claude already mentioned, that ain't going to work on Firefox due following bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1216630
On Tue, Jan 24, 2017 at 6:12 PM, Isiah Meadows <[email protected]> wrote: > To clarify, I'm wanting to know if it's a callable that isn't a class. > Technically, I could use `Function.prototype.toString` for most > practical purposes of mine, but that'd be super slow (I'd need it in a > warm loop), and wouldn't catch native construct-only classes like `Map` > and `Set` (which are still `typeof f === "function"`). > > ```js > var funcToString = Function.prototype.toString > > function isCallable(f) { > return typeof f === "function" && > /^\s*class(\s*\{|\s+[^(])/.test(funcToString.call(f)) > } > ``` > ----- > > Isiah Meadows > [email protected] > > > On Mon, Jan 23, 2017 at 1:49 PM, Jordan Harband <[email protected]> wrote: > > Unfortunately, the only practical way to know that without risking side > > effects is to read the human-produced documentation on the function, or > to > > have a human read the code. > > > > On Mon, Jan 23, 2017 at 8:19 AM, Isiah Meadows <[email protected]> > > wrote: > >> > >> I'll point out that all I need is some way to detect anything that is > >> callable except for classes. Basically, anything that has a `[[Call]]` > that > >> doesn't throw unconditionally without entering a different scope (like > >> classes, but not %ThrowTypeError%). > >> > >> And to clarify, these would both be included per above, since it does > >> enter a different scope: > >> > >> ```js > >> // New language scope > >> function foo() { > >> throw new TypeError() > >> } > >> > >> // New native scope (%ThrowTypeError%) > >> "use strict" > >> var foo = Object.getOwnPropertyDescriptor( > >> arguments, "callee" > >> ).get > >> ``` > >> > >> `Reflect.isConstructor` isn't sufficient for my needs, since it would > >> still consider the first `foo` above to be a constructor. > >> > >> > >> On Sat, Jan 21, 2017, 01:14 Jordan Harband <[email protected]> wrote: > >>> > >>> The reality here is that we're all playing around what the definition > of > >>> "constructor" and "callable" mean. > >>> > >>> In the spec, "constructors" are defined as having a `[[Construct]]` > >>> internal slot; something is "callable" if it has a `[[Call]]` internal > slot. > >>> By that definition (https://tc39.github.io/ecma262/#sec-isconstructor > and > >>> https://tc39.github.io/ecma262/#sec-iscallable), a `class` > constructor is > >>> indeed callable (because it's defined to have `[[Call]]` throw a > >>> `TypeError`). Similarly, as defined in the spec, `typeof class Foo {}` > is > >>> "function" only because it has a `[[Call]]` internal slot > >>> (https://tc39.github.io/ecma262/#table-35); if constructors lacked a > >>> `[[Call]]` slot (such that `IsConstructor` returned `true` for them), > then > >>> `typeof someConstructor` would return "object". > >>> > >>> Obviously the committee could have chosen to define these things > >>> differently; but this is how things are defined. > >>> > >>> > >>> > >>> I'm going to claim that conceptually - eg, to the majority of users - > >>> something is a constructor when it's *intended* to be used with `new`. > In > >>> other words, "what it returns" isn't actually the point - if you're > "meant" > >>> to use it with `new`, it's a constructor, otherwise, it's a function - > and > >>> functions that work with both can be thought of as a dual > >>> constructor/factory (the factory calls the constructor for you). > However, > >>> that conceptual definition is not one that can be programmatically > >>> determined, because "programmer intention" in this regard simply isn't > >>> inherently enshrined in an observable way, whether choosing `class` or > >>> `function`. > >>> > >>> Personally I think it would be wonderful to expose `IsConstructor` > >>> (`IsCallable` is already exposed via `typeof` returning "function"), > but I > >>> feel quite confident that neither actually address any of the use > cases in > >>> this thread. > >>> > >>> In addition, "safe to call" or "safe to use with `new`" all depends on > >>> your definition of "safe", and it's clear from this thread that that > does > >>> not have a universally agreed-upon definition either. > >>> > >>> It might be useful to distill things down to 1) concrete use cases for > >>> calling or instantiating a function where you don't already know what > it > >>> does, and can't assert in your human documentation what you expect; 2) > a > >>> definition of "constructor", either a different one if you don't agree > with > >>> mine above, or if you do, a form of mine that can be programmatically > >>> determined, and 3) a definition of "safe" which means more than > "doesn't > >>> throw an exception". > >>> > >>> On Fri, Jan 20, 2017 at 6:52 PM, Scott Sauyet <[email protected]> > wrote: > >>>> > >>>> Bradley Meck wrote: > >>>> >> 1. every call to `new Foo(...args)` creates a distinct object not > >>>> >> reference-equal to any other such call. > >>>> > > >>>> > Would this mean > >>>> > > >>>> > ``` > >>>> > function factory() { return []; } > >>>> > ``` > >>>> > > >>>> > would qualify as a constructor? > >>>> > >>>> I'm thinking of that as a necessary, but not a sufficient condition. > >>>> > >>>> If it fails that test it cannot be a constructor. It's clear that > >>>> there are other tests. It's not clear to me what they are. > >>>> > >>>> -- Scott > >>>> _______________________________________________ > >>>> es-discuss mailing list > >>>> [email protected] > >>>> https://mail.mozilla.org/listinfo/es-discuss > >>> > >>> > >>> _______________________________________________ > >>> es-discuss mailing list > >>> [email protected] > >>> https://mail.mozilla.org/listinfo/es-discuss > > > > > _______________________________________________ > es-discuss mailing list > [email protected] > https://mail.mozilla.org/listinfo/es-discuss >
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