> > Try `Number.prototype.valueOf.call(obj)`: it will throw a TypeError if and > only if `obj` has no [[NumberData]] internal slot. Ditto for String, > Boolean and Symbol.
I already mention this and demonstrate why it is not sufficient in my example. Reiterated plainly: ```js JSON.stringify(Reflect.construct(Number, [], Number)); // "0" JSON.stringify(Reflect.construct(Number, [], String)); // TypeError JSON.stringify(Reflect.construct(Number, [], Object)); // null ``` Even though both of these have [[NumberData]] internal slots, it also considers the type when throwing. Hence the question if you can type check cross-realm in a way that does not depend on internal slots. On Sat, Aug 4, 2018 at 6:35 PM Claude Pache <[email protected]> wrote: > > > > Le 5 août 2018 à 00:16, Michael Theriot <[email protected]> > a écrit : > > > > `JSON.stringify` has unintuitive behavior regarding interal slots. > > I don’t think that anything involving an object that has a [[StringData]] > internal slot but has `Number.prototype` in its prototype chain could have > an ”intuitive” behaviour... > > > > > > > I think this is related to `Array.isArray`. Is there an equivalent > `Number.isNumber`? Or is this just something only `JSON.stringify` can do? > > Try `Number.prototype.valueOf.call(obj)`: it will throw a TypeError if and > only if `obj` has no [[NumberData]] internal slot. Ditto for String, > Boolean and Symbol. > > —Claude
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