On Aug 13, 2013, at 9:41 AM, André Bargull wrote: >> Hi, >> >> Section 15.19.3.3 of the July 15 draft says: >> >> Properties of the GeneratorFunction Prototype Object >> >> The GeneratorFunction prototype object is an ordinary object. It is >> not a function object and does not have a [[Code]] internal data >> property or any other of the internal data properties listed in >> Table 13. In addition to being the value of the prototype property >> of the %GeneratorFunction% intrinsic and is itself the %Generator% >> instrinsic. >> >> See http://people.mozilla.org/~jorendorff/es6-draft.html#sec-15.19.3 for >> the gnarlies. To be explicit, we are talking about this object: >> >> var GeneratorFunctionPrototype = function*(){}.__proto__; >> >> I think this object should be a function and not a normal object. >> >> 1. The spec doesn't specify any other objects for which "x instanceof >> Function" that aren't functions. > > Isn't that just because no other object inherits from the Function object in > the specification? For example on the user level you can write `class > MyFunction extends Function {}`, where `MyFunction.prototype instanceof > Function` yields true, but `typeof MyFunction.prototype` is still "object". > IIRC Allen even spec'ed GeneratorFunction similar to if it was written in the > class syntax. >
More generally, we've previously discussed and decided to break from the ES<6 convention that built-in prototype objects act as if they were instances of their associated constructors. That generally won't be the case for prototypes defined using a class declarations. We even decided to relax that requirement for the existing built-in, except where it would create backwards compat issues (Function.prototype and Array.prototype appear to be situations where there are such issues.) instanceof is essentially broken when applied to most non-built-in prototype objects because they usually just aren't defined to proper operate as instances of the associated constructor. > >> 2. Function.prototype.toString is the binding for ".toString()" on >> this object, but it is only applicable to function receivers. > > The same restriction also applies to Number, String, Boolean, RegExp and Date > (or rather to the corresponding prototype objects). So this is not a unique > behaviour w.r.t. the GeneratorFunction prototype object. > same basic issue, many own or inherited prototype methods won't work on prototype objects. Allen
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